The following page shows what I went through to convert a 1965 aircooled Corvair engine into an experimental aircraft engine. I plan to install it on my Zenith 601XL, but I bought the engine cores long before I decided on that aircraft. Since experimental aircraft are one of my hobbies, I knew I would eventually need it. Being able to understand that a large part of the cost of a new certified engine has to do with legal expenses and lack of economies of scale, I've always been partial to auto conversions. It's a price driven decision.

It's a pretty common aircraft engine conversion. It was original made by GM, the parts are inexpensive and still available, it's a aircooled six cylinder engine that produces about the right amount of horsepower for a sport aircraft so it's a pretty good choice.


I guess I could start off with some liability statement... there is an inherent danger to experimental aircraft, what I do is not what I recommend you do, buyer beware, you get what you pay for, etc. Also, I am not in anyway affiliated with any other company selling or handing out expertise, parts, or advice and I'm not making any recommendation for or against any item by showing it here. This is just a record of what I have done and although I may make suggestions, I am in no way providing a guarantee or acceptance of your liability.

Also, I do have to tip my hat to those who have come before me and have been kind enough to share their experiences and lessons learned. Thanks to all and specifically to William Wynne and Mark Langford.

And yes, what I have done to my engine conversion will be counter to common practice in some ways: I will be providing a fuel injection system. I will be providing a single coil. I will have a computer that controls both fuel delivery and spark control. I will require a single high pressure fuel pump. If I lose electrical power the engine will quit. If the computer dies, the engine will quit. If my fuel pump dies, the engine will quit. Yep, I know.


I do have to mention one thought and it concerns the crankshaft. It is the crankshaft which limits the ultimate maximum horsepower that a converted Corvair aircraft engine can deliver. Increasing horsepower requires an increasingly large propeller and increases the bending loads on the fourth journal and bearing. John Brannen did an analysis (of which I studied and found to be pretty close) which showed that the bending forces due to the gyroscopic and asymmetric loads are many times larger than the twisting load due to the application of work. In a car, the crank only sees the twisting load. Even with a perfectly balanced and symmetric propeller, huge asymmetric loads are applied at angles of attack other than 0 degrees (P-Factor). The gyroscopic loads are equally large based on the typical props we are using and typical maneuvers that we are flying.

It's a matter of lateral bending that is generated by the prop that must be absorbed by the fourth journal and bearing. Actually, it will eventually be absorbed entirely by the journal. As the bearing wears, it eventually allows the journal to bend as much as necessary to absorb the full force.

It's another engineering balance: You could run the engine at 200 HP with a huge propeller; but the tradeoff would be that the P-Factor and turning rates would have to be excessively limited. Since we generally don't limit our maneuvers based on maintaining the structural integrity of the engine, the propeller size and horsepower should be limited.

Based on historical evidence, this is a reliable 90 HP aircraft engine.


I have made a master checklist of all items and actions needed during the conversion process. Costs, alternatives, and notes are provided so it's a hell of a checklist (if I do say so myself). The method I use to check off items is to fill in the Actual Prices column. Just looking at mine, you can see which alternatives and which parts I choose by the cost of the item ($0.00 means I did something that required no cost, like cleaning a part, or I chose not buy something).

Corvair Master Checklist


Finding the Cores
Engine Disassembly
Electrolytic Rust Removal
MegaSquirt Engine Control Computer
Denso Alternator
Harley Throttle Body
Tapping the Crankshaft Flange
Tapping the Crankshaft Flange, The Easy Way
Snap Ring
Nitriding the Crankshaft
Bellhousing, Case Studs, and Case Assembly
Culver Propeller
Piston Pins and Connecting Rods
Piston Pin Offset
Connecting the Rods to the Pistons
Piston Rings
Compression Ratio
Baffles and Balancer
Heads, First Attempt
Distributor, Oil System, and where to put the Alternator
Mock-up Engine Mount
Buying Accessories
Starter Ring
The Subaru vs Mercury
Building the Starter Ring
Heads, Second Attempt
KR Gathering 2008
Propeller Hub
Bolting the Propeller Hub On
Heads, Third Attempt
Starter Installed
Fuel System
Parting Comments


After a year or so of on-and-off searching, I found someone in Alabama who had several. His father collected the engines for experimental aircraft. He wasn't an airplane guy and wasn't interested in Corvairs. So after a few emails with him, I decided to drive down one weekend. I got four 110hp engines, all were complete, three were '65-'68, one was a '64. I got an extra crank, an extra set of heads, three 12 row fin oil coolers, an extra set of pushrod tubes, an extra set of valve covers, two side draft motorcycle carbs, and a gascolator for my Model-A. It was $400 for the engines, the rest he just loaded into my truck for free. I paid cash and gave his buddy $20 for helping us load the engines. The following is a few pictures of where these babies were hidden...

One in the barn, one in the weeds in front of the trailer...

Corvair Engine Conversion

and two more in the trailer.

Corvair Engine Conversion

This is how you get four engines in a Ford 150. Also, it's well over 1000lbs and that makes for an interesting interstate ride home:

Corvair Engine Conversion


Two engines were sold. I didn't need them and he was planning on converting them for aircraft use. The deal was that he would take the '64 and could pick one of the '65's at $150 each (which was my cost including travel expenses):

Corvair Engine Conversion

OCTOBER 23, 2007


With my workshop built, I have a place to really work on my projects. I built a 4x8 table and will temporarily dedicate it to rebuilding an engine. Since I want to use it in the future for other uses, I covered it with plastic to keep it from getting oily.

The disassembly of this engine is really simple. Given access to a few special tools, a first-time rebuilder should be able to take it apart in a weekend. Also note from the following pictures, I disassemble the engine and lay out the parts so that if needed, I can put them back in the exact same location. Even though several of the parts will be replaced, taking the engine apart thinking that all the parts will be reused is my recommendation. After it's apart and cleaned up, then you have the opportunity to measure, think things through, and then determine what you want to replace. I think on this engine I got really lucky because it appears that this one is a low time engine. I see no need to replace the cam, lifters, pushrods, grind the crank, etc. Had I just ripped it apart and damaged parts or gotten them out of order, I wouldn't have any choice but to replace these items.

I did need a harmonic balancer puller. Autozone has a free tool lending program for special tools like that. I did have to make a flexplate puller out of a pine 2x4 and three 3/8" bolts. Other than that, you only need basic wrenches and sockets.

The only real problem that I encountered was how to knock the heads off. On a new engine, once you loosen the bolts, the heads should slide right off. On an old one, you need to work it off with a mallet. My problem was that in trying to hit the more sturdy parts of the alumninum head, I hit the fins a few times. One fin broke off. Had I been thinking clearly, I would had simply have used a one foot pine 2x2 as a drift between the head and the mallet. Duh. Keep the mallet at a distance from the fins.

The other mildly difficult task was to unbolt the rods from the crank on an assembly that wouldn't easily turn. It was like a puzzle. I would unbolt whatever rod that I could get to, spray everthing with WD40, and see how much I could turn the crank until I could get to the next rod. The problem was that pistons were rusted into cylinders and rods were suck on piston pins so nothing really wanted to move easily. I was calm that day so I was able to gently work the problem until I got all the rods/pistons/cylinders loose from the crankshaft.

Corvair Engine Conversion

Corvair Engine Conversion

OCTOBER 26-27, 2007

I did have three case studs turn out of the case. They were all near the back of the engine at cylinders 5 and 6 (adjacent to the bellhousing). I would guess that that part of the engine when in the car gets hotter causing the stud holes to enlarge (due to excessive thermal cycling between the case and the studs).

There are some that simply cut the nuts off in order avoid turning out the case studs. I would recommend against using pliers or vise grips to hold the stud because that would cut grooves in the side of the stud. I'll either just use oversize replacement studs or Locktight the old ones back in (more research on what is acceptable is needed).

A younger version of me:

Corvair Engine Conversion

Corvair Engine Conversion

This is where it got tricky. You can see where I was able to get to some of the rod bolts, but not all of them on an assembly that wouldn't turn. Although I wanted to a few times, I would recommend against bashing it with a hammer. However, I may have used a wooden drift and a mallet a few times.

Corvair Engine Conversion

Nothing interesting here, I just took the oil pan off to see if I could get to the bottom rod bolts from underneath. You can't.

Corvair Engine Conversion

In my left hand is the flywheel. As you can see in the bellhousing, the flexplate is still connected to the crankshaft flange. Even after the crankshaft bolts are removed, the flexplate was still rusted stuck to the crankshaft flange.

Corvair Engine Conversion

After taking the case off of the engine stand (and putting a second engine on the stand just to show off), I used a pine 2x4 with three holes drilled in it to make a puller. Two outer bolts (about 6" long, I can't remember) were pushed through holes in the 2x4 and threaded into flexplate using the flywheel bolt holes. The 2x4 then stoof off of the the flexplate by about two or three inches so that a third bolt and nut could be placed in the center between the 2x4 and the flange center. The head of the bolt was up against the flange, the nut was up against the 2x4, and the excess threaded part of the bolt extended through the 2x4. The nut was turned to try to push them apart and it eventually pulled the flexplate off of the flange. To say it more simply, the two outer bolts pull the flexplate and the center bolt pushes against the crankshaft. (I wish I took a picture.)

Corvair Engine Conversion

Keeping it organized:

Corvair Engine Conversion

Check out the bolts used as feet so the case wouldn't rest on the oil pan. This is something that will be done during assembly so that if the pan is installed, the gasket won't be subjected to unusual forces causing it to leak.

Corvair Engine Conversion

OCTOBER 31, 2007

The following is an example of electrolytic rust removal. Since rust is held on by a electrochemical bond, the bond can be broken by applying the appropriate electrical charge.

The steps are to submerge the part and a sacrificial piece of steel in a alkaline bath, connect a source of DC power, positive to the steel, negative to the rusty part, and let it go. The rust breaks free from the rusty part and collects on the steel. The best part is that no damage is done to the part. This is really useful when you would rather not sandblast a precision or antique piece.

The alkaline salt used in the bath is sodium carbonate (washing soda, hot tub pH reducer, etc.). It is a stronger base than sodium bicarbonate (baking soda) but harder to find. If you really need some, sodium bicarbonate completly breaks down to sodium carbondate at 400 degrees F (in other words, bake some baking soda and you will have washing soda).

There is all kinds of information on the internet from guys who do this at home, just look up "electrolytic rust removal" for the details. Also worth noting is that when it comes time to anodize your aluminum parts, it's a similar process. The difference is that you will use a acid bath and the connect the positive terminal to the part. In other words, you are trying to "rust" the part.

A really rusty spare crankshaft was used as a test:

Corvair Engine Conversion

Corvair Engine Conversion

Two days later:

Corvair Engine Conversion

The crank was pressure washed (the rust turns to mud and washes off) and then sprayed with WD40. Not to damn bad!:

Corvair Engine Conversion

NOVEMBER 14, 2007

Completely disassembled:

Notice the head, pushrods, exhaust logs, etc. down on the lower shelf still organized. If you think you needed to, you could take a permanent marker and circle, label the parts, and make notes on the plastic.

Corvair Engine Conversion

Corvair Engine Conversion

NOVEMBER 21, 2007

The crank was treated to the same rust removal as tried on the spare and then the journals measured. This crank is still within specifications and will not need to be ground 10/10 undersize (I get lucky every once in a while).

Corvair Engine Conversion


This piston is siezed from the rust on the cylinder. Time for some more electrolytic rust removal.

Corvair Engine Conversion

This is the bag of walnuts shells that I used for blasting the aluminum parts. The 20/30 size (0.0331"-0.0232") is a little large for the screen-door screen I use to screen out the junk and it doesn't flow through very smoothly. After my first batch, I had considered using the next size smaller, but it was 30/100 (0.0232"-0.0059"). Those 0.006" pieces seemed like they would be too fine and would essentially be like dust in a sandblasting operation. I did order a second bag later and I stuck with the 20/30.

Corvair Engine Conversion

Corvair Engine Conversion

Cylinder soup.

Corvair Engine Conversion

After walnut blasting, this is what the case looks like.

Corvair Engine Conversion


The control computer will be a MegaSquirt kit. I used the MegaSquirt II controller with the Version 3.0 control board. A more detailed web page about this phase of the project can be found here:

Corvair-MegaSquirt EFI ECU

To test the board, I first had to build a Stimulator (which provides pretend engine information to the control board so you can test the board without an engine).

Little box full of important parts...

Corvair Engine Conversion

Corvair Engine Conversion

Corvair Engine Conversion

Corvair Engine Conversion

Stimulator complete.

Corvair Engine Conversion

And now I can start on the controller.

Corvair Engine Conversion

Corvair Engine Conversion

The partially complete controller and completed Stimulator are connected to each other for testing.

Corvair Engine Conversion

The following is a small three-wire Denso type alternator. I got this off of EBAY new/rebuilt for $130. It's essentially a OEM replacement part. If you have checked out Mark L.'s website, he noticed this type alternator at a John Deere dealership. You could go to Deere and pay $300 for it, but it will still be the same Japanese/Chinese part shown here.

I opted NOT to get the one-wire racing type alternator in this frame size (available from several sources) since a three wire allows an on/off switch on the panel. Additionally, some of the racing alternators put out a voltage slightly higher than standard and I didn't want that.

Corvair Engine Conversion


A few pictures of the completed controller. The whole project took a week or so of evenings to solder all the parts together. It was way too cold outside to do real work anyway.

Corvair Engine Conversion

Corvair Engine Conversion

Corvair Engine Conversion


I've seen Covair conversions which include fuel injection, but what I can't believe is that no one has thought of this first (so, yes, I am taking credit for this idea). If this is the only thing that I contribute to the common knowledge of Corvair engine conversions, I would be happy.

Harley Davidson has been providing all of their motorcycles with fuel injection throttle bodies for several years. You can no longer get a factory Harley (or Honda, Yamaha, etc.) with a carburetor. This great thing about this is that there are those who will remove the fuel injection system to put a carburetor back on or upgrade the stock throttle body to one that is larger. This means that you can get what I got on EBAY for $99.

A Harley throttle body is sized for engines in the 100 horsepower range. This means that the intake and outlet diameters and the injector flow rates are all PERFECT for a Corvair.

Here's the cool part... look at the design: If you mount it under the Corvair engine and place it upside down, it already has two outlets that turn up a little. This is perfect for two intake runners routed up to the two sides of the engine. It also has a front flange ready for a Harley aftermarket air filter. So there will be no modification required for this body to bolt this to a typical Corvair conversion intake.

Here's a second really cool thing... all the sensors, injectors, and even a throttle cable attachment are included! From the pictures below, you will see (from right to left):

The flanged intake
The throttle plate with return spring and cable mount
The throttle position sensor
The idle air valve
A hose fitting for a prime injection or a remote pressure sensor
The outside air temperature sensor
The manifold absolute pressure (MAP) sensor
Two injectors, one each side
The fuel connection tube
Two outlets
And the whole thing weight a pound or two

The only other sensors needed for a fuel injection system are the crankshaft position sensor (which will provide engine RPM) and the O2 sensor. Both of which are easy enough to find at AutoZone.

It's a bit difficult getting specifications for these sensors since Harley is really secret about their products (it forces you to go to a dealership). However, all of the sensors are Delphi and if you search the internet all week long, you can find what you need. I even found a source for appropriately priced connectors for the sensor fittings. If you look at my Master Checklist, I have the part sources and injector flow rates listed in the notes.

Corvair Engine Conversion

Corvair Engine Conversion

APRIL 2008


As we all know, the threads on the flange are an odd 11/32-24. You've got two choices, either speciality made studs or retapping the holes for 3/8-24. The following is my method for retapping without removing the flange from the crankshaft.

Retapping is fairly easy since the 11/32-24 is only slightly smaller than the 3/8-24 and they are both 24 pitch. Really all that you need to do is knock off the top of the old threads and let the new tap follow the remaining thread. The most critical thing is that you bore straight down the hole.

[ WAIT! Read the following for fun, but the easy way is to simply run a 3/8-24 tap down the hole! No drilling required! ]

First you need to set up your drill press so that the base is down low and set off-center exactly the same as the flange's bolt circle. The flange holes are 1-1/4" from the center of the crankshaft so I marked my drill press base with a marker 1-1/4" from the center of its center bore. I found a straight rod the same length as crankshaft and mounted it in the chuck and used it to point down where the mark should be. I moved the base sideways until the rod and the mark lined up.

You can see how the crankshaft now sits vertically and offset. The pulley end of the crank centers nicely on the drill press base bore. For safety, I installed the pulley bolt but threaded it in only a few turns. This left it sticking out far enough that if I let go of the crankshaft, it sticks far enough into the drill press base bore that it keeps the crank from falling over.

Corvair Engine Conversion

I also double checked square in both directions

Corvair Engine Conversion

Corvair Engine Conversion

In the following picture, look at two things: The hole I'm about to drill and the base down below. the hole and the hole opposite of it should make a line that should be parallel with the base.

Corvair Engine Conversion

This jig is simply a strong arm that keeps the crankshaft from rotating when you drill. It's set so that it hits the post of the drill press. Before you start drilling the crank is essentially loose and you can move it around, but once you start drilling it's held in place by the bit.

Corvair Engine Conversion

This is the only time I have found hand tapping to be easy. Usually if I need to tap, I use the drill press and manually turn the chuck to tap a straight hole. In this case, you just need to be careful and make sure that you start on the existing treads. Go slow, be careful, and use lubricant (Tap Majic, WD40, etc.). Tap a few turns and then back out a half turn to break the chip and blow that out with compressed air.

Also, most of your time spent will be setting things up and building the strong arm. I practiced on my spare crankshaft to make sure everything turned out OK. The real crankshaft I had drilled and tapped in less than 30 minutes.

Corvair Engine Conversion

There is a lot of information in the following picture and if you've never run a tap before, I hope I can help.

There are three general types of hand taps: a taper tap, a plug tap, and a bottom tap. The only difference is how much the first few threads of the tap are ground down so that the edge of the very first thread doesn't have to do all the work. A taper tap is easier to get started by hand because the first few threads don't take off much. the bottom tap is typically used to tap full threads to the bottom of a blind hole (thus its name). In the picture, the top tap is a taper tap and the one below is a bottom tap. The most common is a plug tap (which is halfway in between a taper and a bottom), but in general I rarely use that type because it's hard to start by hand and it won't bottom.

Also, taps come in different sizes for the same size tap. This is called the H-limit. Since you don't want to always press fit the threads together, taps are oversized slightly. A H1 tap is oversized 0.0000 to 0.0005", a H2 is oversized 0.0005 to 0.0010", a H3 is oversized 0.0010 to 0.0015" and so on. I used a H3 and probably would recommend the H1 or H2 for a tigher fit. You can alway retap it larger later, but you can't retap it smaller.

For a 3/8-24 tap, you predrill with a size Q or R bit. The Q is smaller and leaves more metal for threads so I used that. I then hand tapped with the taper most of the way through, and then finished with the bottom tap.

Corvair Engine Conversion


Now, with all that said I am very curious if you just couldn't take a 3/8"-24 taper tap and run it down the existing threaded holes without redrilling. I'll try that next time.

[ I've discussed this with other builders who have tried it... this is the way to go. So forget all that nonsense above, just run a 3/8" tap down the already tapped hole to enlarge it 1/32". ]


Unless you live in a cave, you surely know by now that there are two common methods for ensuring that the crankshaft flange doesn't come off during use. It is only press fit on the crank and potentially could come off if you pulled hard enough (you would probably break the crank first, but if you didn't do something people would question your judgement). The most common is rethreading the inside of the crankshaft and threading in a "safety shaft" (this acts like a large bolt that holds on the flange and the propeller hub). The second most common is machining a groove on the outside of the crankshaft to accept a snap ring. Before the flange could come off, it would have to shear through this snap ring (between the press fit and force required to shear the ring... good luck). Quite frankly, the wooden propellor blades would break off or the crankshaft would break LONG before the flange would even budge.


What I had done a few months ago was to have the crankshaft grooved to accept a spiral retaining ring. This is the WSM-156 and the manufacturer is Smalley Steel Ring Company. I actually tried to purchase the rings from both Smalley and from a separate equipment representative, but when you only need a couple, there isn't enough profit for them to do the accounting. They essentially sent them to me for free as a "sample". It was very kind of them and I hope that the collective Corvair community doesn't take advantage of this.

The stainless steel rings WSM-156-502 are shown below, but I also have the carbon steel rings which I think are a little stronger.

Corvair Engine Conversion


With all the machining done on the crankshaft, it's time to send it off for nitriding. In preparation for that, it needed to be cleaned. So I first scrubbed it with a soft brush and kerosene (next time I'm going to try low-odor mineral spirits; kerosene stinks). To clean off the kerosene residue, I gave the crankshaft a soapy bath. If nothing else, this needs to be done so the post office doesn't have a fit when you try to mail something that smells flammable.

Corvair Engine Conversion

It just seemed really counterintuitive to get a precision steel part all wet; rust never sleeps. After I hosed off the soap and blew off the excess water with compressed air, I baked it at 300 degrees for 30 minutes to ensure that all of the water was gone. Here's my method for baking a crankshaft:

(1) Wait until the wife it gone
(2) Bake crankshaft (it will stink!)
(3) Let crankshaft cool and wrap it with Saran Wrap to keep new mositure off
(4) Get it the hell out of there
(5) Run the self-cleaning cycle on the oven (which smells like hell) to mask the smell of the crankshaft
(6) When the wife comes home, the house stinks because you were cleaning the oven!
(7) Don't let her see this webpage

Corvair Engine Conversion


Pramod Kotwal is a very nice gentleman and I appreciate that he will nitride these crankshafts. I did double check his requirements, and the appropriate methodology is as follows:

(1) Make sure that all machining on the crankshaft is complete
(2) Have the brass distributor gear, spacer, and fuel pump cam removed from the pulley end
(3) Clean and dry the crank as noted above
(4) Make a sturdy shipping crate and pack the crankshaft
(5) Mark the crate
(6) Insure this with the shipper for at least $1000 (it forces everyone to sign for it during delivery)
(7) Send a check for $150 plus the cost to ship it back to you
(8) Include the Release of Liabilty as shown on William Wynne's site

I made the crate from two 24" long 2x8's, some 10" wide 1/2" OSB/plywood, and 3" long drywall screws. I wrapped the crank with old carpet until it fit snugly in the crate. I would have used carpet padding, but they didn't have any of that in the dumpster behind the carpet place.

Corvair Engine Conversion

You can see below how I marked the crate. I included my name, zip code, which end up, and which screws for Pramod to remove and took a picture of it. The picture, my name, and the zip is for when the Post Office tears off the shipping label and loses the crate. I then have something to argue with them on: "See this picture? My name and zip code is on the crate! How could you not know who it belongs to?!" To ship it from Illinois to Massachusetts was $55 including insurance.

Also, I mailed the Release of Liability and the check in a separate envelope. I'm not sure this is a better way for Pramod, but I figure at least he would then have a letter indicating that the crate is coming. Plus, I then didn't have to take a drill-driver into the post office to open, include the check, and reclose the crate (because you don't know how much to add to the $150 for return shipping until you send it).

Corvair Engine Conversion

Holy Crap! Apparently, while I was at the Post Office mailing the crankshaft, the UPS guy dropped off this large box from Clarks. Isn't that irony; I now have all my new parts, but I just mailed my crankshaft away. I should have planned this better.

Speaking of parts... I tried to order all of this stuff back in October when I was taking the engine apart. But guess what, no forged pistons in stock. I had to wait HALF A YEAR until mid-April before they had more in. If you are planning a rebuild and the forged pistons are in stock, get them immediately!

Corvair Engine Conversion

MAY 2008

I used a Sawzall to cut the front cover from the bellhousing. The trick is using the small "scroll" blades to turn corners. I left about 1/8" or more beyond the gasket surface and plan to sand down the excess.

Corvair Engine Conversion

I used a band saw to get a little closer and 80 grit on the bench sander to finish the job. This is what it looks like after walnut shell blasting. It's still stained from the flywheel rust which is why I think most people paint this part.

Corvair Engine Conversion


Since I was at the shop, I also reinstalled the three case studs that came out during disassembly. I know it's common practice to replace the studs with new oversize threaded studs since it is supposed to be a press threaded fit, but I would rather have all the studs to be the same. The new studs may not have the exact same strength (either stronger or weaker), they won't have undergone the same work hardening and thermal cycles, and therefore there is a good possibility that they would elongate at different rates as the old ones. I would rather put the old ones back or replace them all.

My guess is that the original studs were press threaded partially to maximize the thread contact to 100% but primarily so that they would be locked into place. Nowadays, we have thread locker.

Since the studs were still very difficult to thread in and still a mild press threaded fit, I preheated the case to expand the holes. I positioned each case half in front of a kerosene turbo heater (but not too close to do damage) for about ten minutes. While it was hot, I moved it to the bench and applied red thread locker to the stud and threaded it in. There was a notable decrease in the torque required to thread it in while it was hot and the stud was cold. As it quickly cooled, it tighened up so I had to work fast.

A few days later, I sanded and cleaned the case studs in preparation for paint. Since I hate masking, I dropped a washer down the stud to mask off a perfect little circle. The washers get burried in tape.

OK OK, I used duck tape to mask off only because it was on my workbench. It was a pain to get off so I would recommend not using duck tape. And yes, I call it "duck" tape because it sticks to every thing BUT ducts (and it was originally called duck-tape and used by the military for water-proofing). "Duct" tape to me is the foil tape with a peel off backing that sticks to ducts.

Corvair Engine Conversion

Corvair Engine Conversion


Nitron sent the crankshaft back in time for this weekend. I polished the journals with "00" gray Scotchbrite, installed the bearings, and put in the crankshaft and camshaft.

HOLY COW, WHAT ARE YOU DOING? Yep, I'm using the original camshaft! Just like everything else on this engine, it was at new specifications so why trash it? I know that there are several cams that will give two or three more horsepower at lower RPM, but I'm happy with the stock HP curve. The stock curve reads about 90 HP at 3100 RPM but I bet it will be better than that since the intake and exhaust aren't going to be stock and should be less restrictive. Regardless, I would rather have a higher factor of safety against overstressing the crankshaft.

Cam mains were oiled and the lobes were coated with assembly lube. The crankshaft mains were oiled, the journals were oiled, just about anything inside that was steel was oiled.

Corvair Engine Conversion

After a Saturday afternoon of work (mostly double checking things) the case is assembled. The oil plugs are in (they must be put back in before you install the camshaft), the oil seals, the oil bypass spring, the oil cooler bypass have all been replaced, the oil pump has been cleaned and installed, and the case ends have been bolted on. I used antiseize on the case bolts, I used blue threadlocker on the bolts for the case ends and the oil pump cover, and I used Permatex Ultra Black on the oil seals and the corners of the case halves (as opposed to Yamabond). The cam and crank gears and the front oil seal (where it rides on the crankshaft flange) were all oiled. I also installed the snap ring on the crankshaft flange.

Corvair Engine Conversion


I took a trip to Culver Props (Valley Engineering, LLC) in Rolla Missouri and met Father and Son owners Gene and Larry Smith. They and their family were working on the Back Yard Flyer, a new Sport Plane to be shown at Oshkosh 2008. I ordered a wooden propellor while I was there. Larry, Gene, and I came to the conculsion that I would probably be best suited with a 64"x44" prop. I'll be running a stock engine behind a Zenith 601XL. I won't know if this prop is appropriate until the plane flies, but this will at least allow me to bench test the engine.

I didn't take any pictures of their operation, but their web site is full of them. The only picture I took was of the front of my motorcycle. The layer of bugs is what you get for taking an eight hour trip through the back roads of the Ozarks.

Corvair Engine Conversion

A few weeks later it arrived FedEx. Even my wife thought it looked beautiful.

Corvair Engine Conversion

JUNE 2008


I ordered a Chinese 12 ton shop press off of Ebay and received it yesterday. I'm sure I'll need it for something else eventually, but currently I need it to press out the piston pins. Whatever justifies a new tool.

The piston pins (gudeon pins, connecting rod pins) are slip fit in the piston but press fit into the connecting rod. Unlike newer arrangements, where the pin is slip fit in both the piston and the rod, there are no end clips to keep them in place. This means they are a little harder to get out. However, you don't necessarily want to simply press them out cold.

The common trick that I used is to heat the rod end to expand it enough to let the pin press out easier. I first set up the piston assembly in the press mounted on its side on one of the standard press plates. I positioned the pin so that it would pass through one of the notches in the plate (I could have also use a large long-wall socket big enough that the pin would pass inside of the socket). I then used a 6" long 3/8" ratchet extension as a drift pin with the socket end (the fat end) against the piston pin. It presses easily until the side of the rod end contacts the inside of the piston. At that point I put some pressure on it, but didn't try to press the pin out.

Using my acetylene torch with the #0 welding tip, I heated the rod end. I did this gently and kept moving around so I didn't overheat any spot on the rod. I guess I could have used a plumbing propane torch, but using a non-contact thermometer I measured that the rod never got over 350 degrees. In less than a minute, the rod end expands to the point where it can no longer hold the pin against the pressure from the press and "POP", the rod lets go. Working quickly and keeping the heat on the rod, I pressed the pin the rest of the way out.

Sorry, no pictures... after over 10,000 shots my digital camera quit.

While all this was happening, UPS delivered my ARP rod bolts from Summit. Summit also sent a catalog, a hat, and some stickers. Cool.


With the pins out, I immediately blasted the connecting rods clean and pressed out the old rod bolts (I knew I would need my press for something else, I just didn't think it would be so soon). I then weighed the rods and caps:

Rod #1: 380 grams (+2)
Rod #2: 386 grams (+8)
Rod #3: 380 grams (+2)
Rod #4: 378 grams (0)
Rod #5: 393 grams (+15)
Rod #6: 380 grams (+2)

I then pressed in the new ARP bolts. Although it doesn't say so in the short sheet of instructions that come with the bolts, they only fit in one way. This is shown in the pictures below:

Corvair Engine Conversion

I made sure that there was enough clearance so that the threads of the bolt didn't drag along the press plate. I guess I could have also drilled a hole in the plate, but this worked just fine. I did have to make sure that no cheap Chinese paint is rubbed off onto the rod flat.

Corvair Engine Conversion

Using a micrometer, I then measured the length of each bolt (the # next to the following numbers means the bolt installed next to the stamped number on the rod). This will come in handy to check if the bolts have permanently stretched the next time the engine is torn down:

Bolt 1#: 2.0067 (inches plus or minus 0.0003)
Bolt 1 : 2.0095
Bolt 2#: 2.0093
Bolt 2 : 2.0051
Bolt 3#: 2.0062
Bolt 3 : 2.0067
Bolt 4#: 2.0033
Bolt 4 : 2.0083
Bolt 5#: 2.0062
Bolt 5 : 2.0081
Bolt 6#: 2.0052
Bolt 6 : 2.0062

With the rods, caps, bolts, and nuts assembled I was ready to start balancing. You'll notice from the initial weights that the rods span 15 grams so I'll have a little grinding to do. I built a balancing jig in about 15 minutes that's repeatable withing the gram. It's a little jerry rigged, but it will do for one set of rods.

I started with a 2" hole saw and cut a plug for the journal end (the big end) of the rod. The hole saw also makes a concentric center hole. I used a drill bit slightly smaller than the hole saw center bit and drilled into a short piece of 2x4. I used that same bit as the shaft that the plug rides on (the threads are then pushed into the 2x4, the smooth shank sticks out as the shaft). I screwed a base on the bottom of the 2x4 to make it more stable.

I then took a welding rod (a coat hanger would work) and bent it so it would hold a socket at 90 degrees. The other end was bent over and hung from the upper support of the shop press (I'm using the press only as a frame for the whole get-up). The socket/rod is free to swing easily from side to side.

The important point is to support both ends of the rod by the centered peak of the hole at each end. The reason for the round "bearings" (the wood plug and the socket) is so that they roll to the peak of the holes and the rod is supported at the same point during all measurements. If you move the support to the left or right by only 1/16" of an inch, you'll be off by up to 10 grams.

Corvair Engine Conversion

I'm not planning on measure the small end with this jig. If I get the total weights the same and I get the big end weights the same, the small ends must be the same. Before any grinding the big ends weighed:

Big #1: 288 grams (0)
Big #2: 300 grams (+12)
Big #3: 292 grams (+4)
Big #4: 290 grams (+2)
Big #5: 301 grams (+13)
Big #6: 294 grams (+6)

The rods with the bolts and nuts:

Rod #1: 431 grams (+2)
Rod #2: 437 grams (+8)
Rod #3: 431 grams (+2)
Rod #4: 429 grams (0)
Rod #5: 444 grams (+15)
Rod #6: 431 grams (+2)

As you can see by the total weight of the rods before and after the ARP bolts and nuts are installed the weight differences stay the same. Therefore, the ARP bolts and nuts all weigh exactly the same. Quality!

Since #4 has the lightest total weight but +2 grams on the big end, I will need to grind off 2 grams from the big end to make it lightest on both measurements. This becomes my target. To put things into perspective, a dime weighs just over 2 grams. I'll then work each rod one at a time to match to the target rod.

After a bit of grinding, I got them all within a few grams. I would have liked to lighten the heaviest a little more, but I ran out of material to safely remove. If they were new rods and had never been run together as rod/cap combinations, I would have switched rods and caps around to get them to initally be more closely weighted. The final weights were:

Rod #1: 429 grams (0)
Rod #2: 430 grams (+1)
Rod #3: 430 grams (+1)
Rod #4: 429 grams (0)
Rod #5: 434 grams (+5)
Rod #6: 430 grams (+1)

Big #1: 291 grams (+1)
Big #2: 295 grams (+5)
Big #3: 291 grams (+1)
Big #4: 290 grams (0)
Big #5: 296 grams (+6)
Big #6: 294 grams (+4)

The small end weights were calculated from subtracting the big end weights from the total weights above:

Small #1: 138 grams (+3)
Small #2: 135 grams (0)
Small #3: 139 grams (+4)
Small #4: 139 grams (+4)
Small #5: 138 grams (+3)
Small #6: 136 grams (+1)

And really this may have been a little overkill since this engine will never go much more than 3000 RPM. Here's what they looked like after:

Corvair Engine Conversion


The piston pins were offset from center by about 0.057 inches. You may be able to see it offset to the left in this picture:

Corvair Engine Conversion

This means that they are directional and proper orientation must be maintained during assembly. That's what the little arrow on the top of the piston indicates. In general, the arrow or notch points to the flywheel but I felt better by researching why the pin is offset so I wouldn't have to rely on generalities. You can see the arrow on the markings below:

Corvair Engine Conversion

Why is a piston pin offset?

In a symmetrical piston, when the crankshaft reaches the top of it's throw, the piston is at top dead center (TDC) and the rod is straight between to two. At this point, the entire rod and piston change direction (from up to down) all at the same time. Because the entire assembly has to change direction simultaneously, this creates the largest force against the crankshaft possible (and the highest vibration amplitude).

Additionally, when the piston is being pushed up on a compression stroke, the rod pushes the piston against one side of the cylinder wall since the rod is at an angle. When the assembly reaches TDC and the power stroke starts, the angle of the rod passes through zero and changes to the other side and the whole piston slaps over to the other side of the cylinder (remember, the piston isn't as big as the bore and it has a little bit of room to move from side to side).

To reduce the problems associated with the above two conditions, the pin is typically offset opposite the direction of the crankshaft. In otherwords, if the crankshaft turns clockwise, the pin is offset counter-clockwise. The result is that the piston reaches TDC just before the crankshaft reaches the top of its throw. This means that change of direction of the rod isn't all at the same time; the top of the rod starts downward sooner than the bottom of the rod. This decreases the instantaneous force required to change the rods direction.

Also, since there is more surface area of the piston face on one side of the pin than the other, the piston has a tendency to rotate in the bore; the compressed gasses push more on one side than the other with respect to the pin. Since the rod is usually pushing it against one side of the cylinder or the other due to its angle, this only comes into play when the rod is straight with respect to the cylinder (which is the intention). When the rod is parallel to the cylinder (at about TDC), the piston rotates and the skirt touches the other side of the bore. When the angle of the rod switches sides, the rest of the piston follows the skirt as its pushed over by the rod. Therefore, the whole piston isn't slapped over all at once.

Below is some pictures trying to explain the above.

Here we have #2 piston on a compresion stroke. From this view, the crankshaft is rotating counter-clockwise (going down), the pin is offset up (toward my thumb), and the piston is pushed against the down-side of the cylinder bore (toward my little finger). I've exaggerated the angle of the rod to make things obvious.

Just to be clear, in this view up is up, down is down, TDC is left. The down-side is down and the up-side is up. (I don't think I helped clear things up.)

Corvair Engine Conversion

When the rod is parallel with the cylinder, it's no longer holding it agains the down-side of the bore and the piston rotates. The skirt moves over to the up-side of the bore.

Corvair Engine Conversion

Finally, during the power stroke the rod pushes the whole piston against the up-side of the bore.

Corvair Engine Conversion

As mentioned before, pin offset also changes the point at which TDC is reached by the piston. With a 2.94" stroke and a pin offset of 0.057" opposite of crankshaft rotation, this gives about a 2 degree advance with respect to the crankshaft.

One final comment. The method to avoid a simultaneous change of direction of the piston and rod without offsetting the pin is to offset the cylinder bore with respect to the top of the crankshaft throw. To my knowledge this is not done on the Corvair. However, a combination of pin and bore offset is common on current production engines. I note this here to indicate that there are different methodologies should further research on the subject reveal new and confusing uses of "offset".


I first measured the weights of the pistons and pins. They were all 538 grams except for one at 539 and one at 545. The heavy one I tried to grind off a little on the inside, but soon realized that a lot of material would have to come off to loose 7 grams. I then measured the pistons and pins separately and found that the heavy combination was partly due to a pin that was 3 grams heavy. I switched around pistons and pins until I had the following weights:

Piston #1: 540 grams (+3)
Piston #2: 538 grams (+1)
Piston #3: 539 grams (+2)
Piston #4: 541 grams (+4)
Piston #5: 537 grams (0)
Piston #6: 538 grams (+1)

I also arranged their order so that the heavy pistons would be with the lighter rods. The piston, pin, and rod final weights were:

Piston #1: 969 grams (+1)
Piston #2: 968 grams (0)
Piston #3: 969 grams (+1)
Piston #4: 970 grams (+2)
Piston #5: 971 grams (+3)
Piston #6: 968 grams (0)

Hold on... I know you aren't supposed to switch pins around; the pins and the pistons are matched sets to something like 0.0002". However, at that clearance if they were plus or minus anything, one of the larger pins would have been a press fit with one of the smaller holes. Since they all slid in the pistons with equal pressure (you could hold the piston with the pin upright and watch as gravity pulled the pin in slowly), I figured they were all sized appropriately.

Installing the rods to the pistons isn't difficult, but it's fairly exciting. I placed the piston face down on the table noting the arrow direction. The pin is halfway installed and ready to be pushed through the rod and the other side of the piston. I then hung the rod with the little end hanging in the air and also noted the orientation (the factory stamped numbers should all end up at the top of the case). I did a practice run of grabbing the rod and putting it down into the piston to make sure that I would naturally stick it in there correctly. You really don't have time to think about it when you're actually doing it.

Using my torch, I gently heated the little end until the non-contact thermometer read 550-600 degrees. (Yes, this is a little too hot since it's in the tempering range... but tempering requires hours at this temperature.) This took about two minutes. The big end is still cool enough to grab with your bare hand. In one quick motion, I put down the torch (without even turning it off), grabbed the rod with my right hand, grabbed the piston with my left, and pushed the pin through with my left thumb.

At first, I measured and marked the pin to know how far it should be pushed into the rod but that really didn't work out. The second one I watched how far the pin stuck out of the other side of the piston. By eyeballing it, it's about 1/8". Of the six, I probably have two or three that are up to 1/8" off and need to be centered on the rod with the press. I'll have to heat the rod to do that so I'll let everything cool off first.

WORK FAST! By the time I stopped heating, I had about 6 seconds before the rod cooled to the point where it would lock on the pin. Having a helper to hold the torch would be a good thing. Making a jig with a stop that you press the pin up against would also be a good thing. Freezing the pin might buy another second.

Corvair Engine Conversion


Earlier this year, I shopped around for someone locally that could rebore my cylinders. My cylinders were in great condition, were at factory new specifications, and if it weren't for the small pitting due to sitting for years I could have gotten away with a little glaze breaking and a stock bore. However, that is a trade that no longer available locally. I guess car engines don't get rebuilt anymore; just melt them down and make new ones. I eventually found a company within 100 miles, but it was simply cheaper and easier to get reconditioned cylinders from Clarks. This way they are also matched with the 0.020-over pistons I purchased from them.

And Clarks does a great job. They came to me sandblasted clean, bored, honed, and oiled.

Since they are cast iron, they will rust unless they are painted. First a quick bath to scrub clean the oil off of the outside so the paint will stick. The inside needs to be cleaned to make sure that no particulates are left from the sandblasting and machining.

Corvair Engine Conversion

Blow dry with compressed air and bake at 250 degrees for 20 minutes. Again, this is one of those operations I wanted to be quick with. There's no sense on making new rust on clean parts. And yes, my wife was gone for the day and did not catch me with engine parts in our oven.

Corvair Engine Conversion

This is what she gets for leaving real-estate information posts in the garage. They make real handy stands. I used a rake handle and a hoe for the rotisserie and I could rotate them to turn the cylinders over to paint all sides. I masked off the outside ends that don't need paint and rolled up a piece of paper and slipped it into the cylinder to keep overspray off of the bore.

Corvair Engine Conversion

Corvair Engine Conversion

I have to give my 5-year old credit... I gave the cylinders an hour or so to dry after painting and then it started to rain. "Oh crap! I've got to get those cylinders before they rust!" I run out, grab the first one and put it in the garage. I run back, get the second, and put it in the garage. I run back to find my 5-year old standing over the rest of them with an umbrella. Nobody told him to do it, he just did it. What a good kid.


To check ring gap, everyone knows that you put the ring in the cylinder, push it straight with a piston, and check the end gap with a feeler gauge. The real trick is getting the springy ring in there in the first place. I think the approved method is to spiral the ring in (start with the ring flat, push one edge at the gap in first, and then work around to the other edge). This has the tendency to spring out at you. It's much easier if you stand the ring upright with the gap at the top and slide the ring in about 1/4". Then all you have to do is carefully rotate the ring down in.

Corvair Engine Conversion

The rings came in a box with very little instructions. It basically indicated how the get the oil ring on and which end of the compression rings were up. But which ring is the top ring? The top ring is plain flat ring (and in my case it was chromed). The second compression ring (the "scraper" ring so-called since it scrapes off the excess oil on the downstroke) is the "reverse torsional taper-faced compression ring" or simply the one with the back bevel. I had to look that all up on the Hastings web site.

Corvair Engine Conversion

The rings were spiraled onto the piston (keeping the sides of the piston oiled so not to scratch), the ring gaps were positioned per the shop manual, the piston was positioned in the ring compressor, and slid into the cylinder. The base gasket was sprayed with gasket prep, and the whole mess was installed into the case.

The correct orientation for the cylinder it to have the square boss up and to the right of center as you look at it from the head end. Or, there is a large relief cut at the base of the cylinder and this should be to the right. Since the cylinder boss/relief is always to the right and the piston arrow points back to the crankshaft flywheel flange, the piston-cylinder orientation for the right side of the engine will be different from the left. If you install the piston in the cylinder the wrong way, you can alway spin the piston but the rings will spin with the cylinder and change the gap locations.

Corvair Engine Conversion


The stock 164 (163.57) cubic inch engine has a 3-7/16" diameter bore, a 2-15/16" stroke, and a specified compression ratio of 9.25:1. What is unknown is the volume of the combustion chamber (the un-swept volume located in the heads) but this can be calculated with the following compression ratio formula (compression ratio equals big volume divided by small volume): 9.25 = ( V + 163.57) / V ... This works out to: V = 19.83 cubic inches.

So why work that out? With a 0.020" over piston, the new displacement is 165.50 cubic inches. The new compression ratio (assuming that V does not change) is 9.35:1. I guess the real question is whether I can run pump gas or if I'm going to need high octane stuff. I can't use aviation 110LL because the lead will foul the O2 sensor, so I'm looking at my alternatives.


The advise given to most builders is to replace the lifters. This is common practice whenever an engine's cam gets replaced. I am reusing my cam and saw no need to replace the lifters. I simply took them apart, cleaned them, and reassembled them.

Additionally, the original Corvair lifters and what is available now as a replacement may not be exactly the same. Because the lifters and pushrods are horizontal, the original Corvair lifters had deeper push rod cups. This would help keep the rod ends in the cup if the assemlby loosened up beyond what the lifter could correct for. More importantly, the Corvair rockers are oiled through the hollow pushrods by pressure created in the lifters. There is some question whether replacement lifters are designed to provide the correct quantity of oil.

However, it is common practice to simply use small block Chevy lifters. Apparently, even Chevy stopped providing dealerships with the Corvair lifters at the end of the 1960's and the official replacement part was a standard small block lifter.

From left to right, you will see below the lifter body, the plunger spring, the plunger, a disk below the push rod cup, the push rod cup, and the lock ring. The plunger has a check ball and spring in the retainer (the extension at the plunger bottom) pressed into the plunger base. The check ball needs to be checked with a toothpick to see if it moves freely.

Corvair Engine Conversion


I sandblasted the cylinder baffles to get them ready for paint. They cleaned up very nicely as can be seen in the before-and-after picture below.

Corvair Engine Conversion

I also sandblasted the valve covers at the same time. The valve covers will be painted only on the outside; the inside will be oiled. I didn't want to run the risk of paint flaking off and getting into the engine.


Since my engine did not come with a harmonic balancer, I had to get a rebuilt one and pay the core charges. Fortunately, I did have the bolt and the thick washer. I used assembly lube on the surface that the oil seal rides on, blue threadlocker on the bolt, and torqued it down to about 45 foot pounds. Obviously, before I assembled the case, I reinstalled the distributor gear, the spacer, and the fuel pump eccentric.


Since I had not yet done it, I first pulled out all the push rod tubes. I removed their O-rings and set them aside for later.

I pulled out the nail and bracket that holds the carburetor springs (or whatever they are). Since they were in very bad condition, I removed the exhaust bracket studs. They all came out with a little work except for one. I tried vice grips and it did not budge. I tried larger vice grips and heated the aluminum and it did not budge. I clamped the stud in a bench vice, heated the aluminum, and it did not budge. Finally, I cut the stud off, drilled it out, and retapped the hole. Oh well, I'll have five 5/16"-18 studs and one 3/8"-18. If the original studs can be cleaned up by cleaning and chasing them with a die, I would suggest leaving the originals in.

I was initially on the fence about either using the stock intake bosses or cutting them off until I noticed that one of the carburetor studs were broken in the threaded hole. So I simply cut the bosses off and plan to mill them flat and drill and tap new holes on the intake log. Some builders have been welding intake tubes onto the logs but that doesn't seem very practical.

Corvair Engine Conversion

Not wanting to buy, rent, or borrow a valve spring compressor, I used a trick that many shadetree mechanics use. I simply pressed them down with a drill press. Some guys take a old socket and cut a window into it and use that as the pressing tool. I just chucked up a punch, put a short socket below the valve, and pressed down on the spring retainer. The socket sits on the bed of the press base to give the valve face something to stop against (you can use whatever fits into the head and is about 3/4" tall). Once the spring and retainer is pressed down, I just picked out the two retainer locks.

Corvair Engine Conversion

One head took about five minutes. Since pressing them with a drift puts a little pressure on the side of the valve (the spring twists a little bit) I will be using an actual spring compressor to install the new valves.

So I messed up and mixed my walnut shells with my sandblasting sand so I can't blast the heads clean (sand + aluminum = bad). Just like I've been told, I took them to the local transmission repair joint. It cost $10, but it took them three days to get around to it. When I got them back, they were cleaner, but not clean. The oil came off and some of the dirt, but I still had substantial carbon and rust to deal with.

Corvair Engine Conversion

While I was looking them over, I noticed that three or four of my sparkplug holes have the threads partially stripped out. You can still thread in a plug, but I worry. Fortunately, I have a whole other set of heads and there plug holes are OK. Now, which is less work... starting from scratch or rethreading the holes?

Corvair Engine Conversion


Totally discouraged with the head situation, I temporarily moved on to other matters. I started with the distributor and took it apart to clean it. Since spark will be controlled by the computer, here is all the parts I WON'T need:

Corvair Engine Conversion

The distributor looks empty without them. Inside, you will still find the spring bottom plate (which is pressed on the shaft), the spring top plate (to keep the cam on), and the cam (just because I need the top part where the rotor sits). When it's time to get things finished, I'll pop on a new rotor and cap. I also removed the gear so I can later spin the distributor shaft with a drill, drive the oil pump, and use it to pre-oil the engine. Yes, I will eventually put the gear back on.

The really nice thing about the transmission joint's dishwasher is that they got the oil cooler really nice and clean. I was concerned about what was still in the cooler so I filled it with solvent and blew it out with compressed air a few times. I had previously cleaned the oil cooler case adapter and the oil filter cover so I just bolted everything on.

Corvair Engine Conversion

There are three holes up on top of the oil filter cover (well, four if you count the one for the oil filter bolt). The two bigs ones are for the oil filler, of which I will relocate, and the fuel pump, of which I won't need. Those two I will plug. The third smaller hole is for the oil pressure sender and I need that.

Now I'm sure this has been done a thousand times before, but I took the alternator and walked around the engine to find a suitable place for it. What about here? What about there? I originally planned on hanging it here:

Corvair Engine Conversion

However, the belt comes really close to the distributor bolt and would hit it under vibration. Plus the damn thing is hanging out there in mid-air.

Not only does this thing need to be located properly, but I really didn't want to cut any part of the case for belt clearance. Also, because it's longer than the commonly used dynamo, I can't place it similarly up front.

So how about here?:

Corvair Engine Conversion

The origional belt was routed about as shown so its got the clearance, and the oil filter cover has unused threaded holes at each end. I just need to fabricate some brackets. This seems like the most likely place for it. I do have to thread in a fitting to turn the oil pressure sender. Plus, the whole thing has to fit under the cowl (the top of the alternator will be about 6" above the top of the case).

Speaking of alternator size, the picture below gives an idea of its dimensions.

Corvair Engine Conversion

JULY 2008


With this alternate alternator location, I'm pretty sure that it'll be too high for a standard 601XL installation. If the thrust line of the engine is located at the top longeron, the alternator will be sticking out the top of the cowl. I drew the layout on CAD and confirmed this.

At this point, I need a preliminary engine mount that I can install everything on and see where I am. Killing two birds with one stone, this will also be my test mount that I'll first run the engine on.

Using 2" angle and 1/2" black iron pipe, I mocked-up the "tray". I had previously cut a firewall and I mounted weld tabs to it. To get the tray and firewall oriented, I used my CAD layout to design a couple of jigs. These were plotted on paper, and then that was spray tacked to 1/2" OSB, and the jigs were cut on the table saw (this was all faster than programming the CNC). The jigs held the tray in place while I filled in the rest of the stand.

Corvair Engine Conversion

A few hours later I had the whole thing MIG welded. The pipe was too thick for my torch to Oxy weld it, and the experience tells me that a TIG welder is in my future.

Corvair Engine Conversion

After this picture, I gave the mount a quick sandblast and hit it with bit of red paint.

A got a little busy with my day job so two weeks went by without any progress. Well, I can't say without ANY progress because I was stuck in front of the computer and had my credit card in my pocket... a dangerous combination! I ordered a bunch of small but important stuff needed to get this thing running. In the picture below there is:

The coil
The oil pressure gauge (for the test stand)
The oil pressure sender
The oil temperature sender
The air/fuel gauge
The O2 sensor (I'll need a second one)
The external fuel pump
The fuel filter
The fuel regulator
The Mecury Marine starter
The starter solenoid
The starter ring (infilled with cardboard temporarily), and
The VR sensor

Corvair Engine Conversion

What you don't see is the Subaru Starter, engine mount rubber bushings, aluminum fuel tubing, a whole mess of AN-6 fittings, and the tubing tools.


Speaking of the starter, I'm taking the path less taken here. Because I'm using a front starter and the engine turns clockwise (CW), I need a starter that turns counter clockwise (CCW). The gear-reduction Subaru starter is very popular for this application because is has a standard CW starter motor that turns a geared output shaft that then turns CCW. This gear reduction also provides higher starting torque from a smaller motor.

I researched starters and found a potential alternative in a starter from a Mercury outboard boat motor. It's a simple starter: just a motor and a bendix drive. It has no protruding mounting ears; it's a face-mount motor. In the back of the motor it has a small hole that your finish drill and tap for your application. It should be pretty easy to fabricate a simple mount for this configuration. The motor is also about 50% longer than the motor on the Sabaru (meaning that it is probably a stronger motor) but it is not geared down. So I'm hoping it will be strong enough to turn the Corvair, but I don't know. It's typical application is for a 90 HP two stroke outboard (about half the displacement of the four stroke Corvair).

Now both of these starters have a 10 pitch pinion gear. This got me thinking and doing some research...


A brief lesson on tooth pitch. On spur gears and ring gears the tooth pitch is in Diametral Pitch (DP). This is different than the way screw pitch is defined, which is in teeth per inch length. Diametral Pitch is teeth per inch pitch-diameter. So if I have a 15" pitch-diameter gear with 10 DP teeth, there will be 150 teeth on that gear. Also, pitch-diameter is diameter where the two gears meet so it's somewhere in the middle of the tooth; it's not the outside diameter of the gear (a common mistake).

The early problems that auto manufacturers had was that they needed really big ring gears and really small pinion gears and the geometry of standard teeth was inefficient. What they did was modify the standard teeth on the ring gear and came up with a hybrid tooth. There's more to it, but if you ever see a "10/12 pitch" it is basically a 10 pitch tooth that has the height of a 12 pitch tooth. Really, I don't care that much, I just need a 10 or 10/12 pitch ring gear to closely match my 10 pitch pinion. If I had to pay for warranty recalls because of the excessive wear on thousands of starts of millions of vehicles per year, I would be more worried.

PROBLEM 1: What is currently commonly done is to use a flexplate off of a Ford Taurus. It's inexpensive and light and the diameter is about the right size at 11.3" OD. The only problem is that it's 12 pitch.

PROBLEM 2: I'm going to need a trigger wheel for the VR sensor on the engine computer. I had planned on hanging one off of the harmonic balancer, but the diameter needed to clear the balancer is almost as large as the starter ring.

SOLUTION: I might as well build a flexplate which has the openings needed for the VR sensor and uses a ring gear that's 10 pitch.

So, I track down a website for a OEM manufacturer that was kind enough to list all of their products, including ring gears. Venture Products International ( lists essentially every automotive ring available. So I just went down their list. At the same time, I was on the AutoZone website to see if those parts were available. Since they are industry standard OEM parts, the part numbers match for both companies (a FRG-135A is a 12 pitch 135 tooth Ford gear at both companies).

I picked a FRG-109V, 10 pitch 109 teeth 10.7" OD which turns out to be from the 1960's Volkswagens. There were a couple of Nissan and Toyota gears that were slightly smaller, but the 1960's gear just seemed right. The FRG-109V was $23 at AutoZone. The Taurus gear was $22, but if you are going to build a flexplate why build one based on a 12 pitch gear?! Also, I could have gone the same diameter as the Taurus ring by using a FRG-114A from a 1991 Honda Acura (10 pitch, 114 tooth, 11.5" OD), but where's the fun in that?

I've designed a few flexplate templates and the file is here: Trigger Wheels


Here is the Subaru (8 pounds 2 ozs) with the 109V:

Corvair Engine Conversion

Here is the Mercury (7 pounds 4 ozs):

Corvair Engine Conversion

You should notice that the Subaru is too high for this smaller diameter ring. It will work if I flip it over, but then the motor housing is really high (I'm going for low profile here) and the electrical connection is against the engine (not good). The Mercury starter, which fits nicely, would be installed with the top of the starter 3-3/4" off of the engine case.

Here's a side view also showing my squirrly idea of mounting the alternator on top.

Corvair Engine Conversion

This gear is small enough that the completed flexplate can be mounted directly against the crankshaft flange without an offset needed for clearance. You can also see in this picture below the planned openings to act as "teeth" for the VR sensor.

Corvair Engine Conversion

While I was goofing around the shop, I figured I would paint the engine test mount and take a picture. I'm sure it will get hidden from view once I start hanging everything from it.

Corvair Engine Conversion


So I plotted a template and, using some 3M Super 77 spary adhesive, stuck it on a sheet of 12 gauge (about 0.105") steel.

Corvair Engine Conversion

I then used a band saw to rough out the diameter. I also center punched each drill location, ran a 3/32" drill through, on the larger holes opened it a bit more with a 3/16" drill, and then finished drilled with the sizes noted.

Corvair Engine Conversion

I needed to mount the flexplate on the lathe, so I turned a shoulder on a piece of 2" black pipe to fit into the crush plate from the origial flywheel. A little welding keeps the two together. I then chucked the homemade flange in the lathe and then faced the front. I bolted the flexplate to the flange and re-chucked it a couple of times until it turned fairly concentric.

Corvair Engine Conversion

Once the assembly was chucked in the lathe, I did not remove it until I had both the outside diameter and the center hole turned so that they would be concentric. The center hole will register over the crankshaft end so it was opened to just under 1.56" (it slip fits on the cranshaft end ensuring that the flexplate is mounted centered). The outside was turned down until the starter ring slipped tightly on.

Corvair Engine Conversion

Almost finished, but I couldn't help myself and mounted it just to see it. I still need to weld the ring to the flexplate and open the VR "teeth" slots.

Corvair Engine Conversion


I did a little research on fixing the sripped out spark plug holes. I could use a Heli-coil or a Time-Sert insert to replace the threads, but I leaned more to the Time-Sert style and they were expensive. I thought about drilling out the 14mm spark plug hole and retapping it for a 18mm taper spark plug, but the tap was about $20. This doesn't sound like much, but I have a second set of spare heads that just need to be cleaned... so that's what I will use.

With a new bag of walnut shells in hand...

I emptied my sandblaster and put in a little walnut shells. After a few seconds of blasting from a new bag of walnut shells made me remember the initial problem I had on the first bag. The shells are still a little damp and full of dust. The first bag I simply ran through the blaster once in the finishing room. The dust was captured by the dust collection system and the shells has a chance to dry on the floor. I then swept them up, screened them once, and they were good to go.

Since my finishing room is now clean and I'm using it to paint, I had to blast outdoors and this means that any media I use is going to be lost in the yard. I couldn't use the walnut shells. So I filled the sandblasted with old shells and sand (they were mixed already and was planning on throwing it all out). The second set of heads were sandblasted on the exterior only. Any part of the head that sees internal engine parts was left for me to clean with a brush (actual sand embeds itself in soft aluminum and then comes loose when things get hot - bad for engines).

I also painted the pushrod tubes and a replacement valve cover. I found that one of the original covers had a small hole in it.

Corvair Engine Conversion

Wait a minute... I was supposed to be working on the heads.



Nothing like getting busy at your day job to kill progress on your airplane.

I haven't made much progress on this project, but I at least got to go to Mt. Vernon to the KR Gathering and meet some of the other Corvair builders. It was very nice to shake hands with some of the guys I've been keeping up with on the internet but have never met.

It was also a real treat to sit in on the engine forum and listen to Mark Langford speak on his experiences, including flying behind a "fifth bearing" equipped Corvair.

Corvair Engine Conversion


Nothing like buying a $1500 lathe to keep from buying a $500 hub. Well, I always wanted a lathe; this helps justify it.

I started with a 6" round of 6061 aluminum 8" long and then cut off a hunk.

I got the round from Shapiro Supply in St. Louis. I've actually been to Shapiro before, but this time I bought from their Ebay store. When I get to the point where I need aluminum sheet for the Zenith 601XL, I'll get if from Shapiro. They are generally a little cheaper than Wicks and just as close.

Corvair Engine Conversion

I chucked up the round and faced, centered, and turned the outside down a little. This is the propeller side but it's not yet finished. I really just need a good surface for the next step.

Corvair Engine Conversion

I rechucked the round using a chuck with independent jaws. This take a lot of time because I needed to get it flat against the chuck and concentric. I did get it mounted with plus or minus 0.001" runout. I then turned down the back side of the hub.

Notice that radius. Not perfect, but I freehanded it. Not bad since the last time I ran a lathe was 1993.

Corvair Engine Conversion

What you don't see in the picture above is that I opened up the back side and bored it out to slip fit on the crankshaft nose.

For drilling the bolt pattern it would have been real nice to have a knee mill with a DRO, but since I don't I had to use another trick. The first step was to mark the bolt circle. I did this on the lathe just after I turned the back side. Using the measured outside diameter of the hub and subtracting the bolt circle diameter, I knew how much further in I needed to mark the circle. I then registered the point of the tool against the outside of the hub, moved the cross slide in the calculated amount, and cut a shallow groove. You can see it if you look real hard.

I then plotted to scale the bolt pattern, cut it out, and glued it on the hub using the groove as a centering guide. I then center punched the spots making sure the punch was in the groove and lined up with the pattern.

Corvair Engine Conversion

I then used a center drill to start the hole, followed by a 3/16" drill for a pilot, and then increased several times until I bored through with a 3/8" drill. It's modestly accurate. By the time I was finished my holes were where they should be within plus or minus 0.005" or so. I will need to open the holes up to allow some clearance which is OK as long as I don't get too carried away. The hub will register off of the crankshaft for concentricity and the torque will be taken up by the surface friction between the hub and flange (and not by shearing through the bolts). So a little clearance between the bolt and the hole should be just fine.

Before I opened up the holes, I needed to counterbore the front side. The pilot on the counterbore requires a 3/8" hole. Also, the counterbore needs to be done prior to turning the step on the front which the propeller registers off of. Cutting the step first would cut away over half the pilot hole and would make it very difficult to bore.

My counterbore is 25/32" since that's the outside diameter of the socket wrench that will turn the bolt. It would be a rookie mistake to counterbore for the head of the bolt only.

[In hindsight, 25/32" is a little tight. I would recommend a little bigger.]

Corvair Engine Conversion

Then back on the lathe taking my time to get it to turn within plus or minus 0.001". I then turned down the front to create the step for the prop, finished sized the outside of the hub, chamfered the edges, and cut a shallow 4.375" diameter groove to mark the propeller bolt circle.

Corvair Engine Conversion

I drilled the bolt circle for the propeller and the hub was finished.


The next step was to get the hub, flexplate, and the crankshaft snap ring to work together. If I slid the flexplate on as-is, it would smash against the snap ring before it would press flat against the crankshaft flange. If I put a spacer inbetween the flexplate and the flange, the hub would be too far out to slide on the end of the crankshaft. So I turned a pipe down to 1.560", the diameter of the crankshaft nose, and used it to align the flexplate and hub concentrically. I bolted the two together, removed the pipe, and the match drilled and pinned the two. Then I removed the bolts, separated the hub and flexplate, and bored out the flexplate center to 1.800" so it would fit over the snap ring. I was then able to reconnect the hub and flexplate using the pins.

With all that done, I welded the starter ring to the flexplate, sandblasted, and painted it.

To me, this was the moment that the Corvair engine converted from an automobile engine to an aircraft engine...

Corvair Engine Conversion

Corvair Engine Conversion

Yee Ha!

Corvair Engine Conversion



I cleaned my second set of heads only to find that two of the cylinders apparently had to deal with broken metal. There were several impressions where it appears that something got caught between the head and the piston. It may have been just fine if I cleaned them up and knocked down the high spots, but I do have a third set of heads to try.

So I pulled the heads off of my spare engine and cleaned them up. They weren't perfect either, but they are the one's I will be working on. I'll likely rebuild the second set too and use them as a backup set. And by the way, walnut (or non-sand media) blasting is the only way to clean the heads. A pressure washer doesn't do diddly and soaks your shoes and pants - it's a big waste of time.

My plan was not to modify the heads at all and then bolt on an intake tube straight to the stock carburetor boss. However, I broke two or three of the carb hold down studs during disassembly so it seemed easier to cut the boss off, mill a new flat surface, and put in new studs than to mess with the remains of the broken studs. With a band saw, each boss comes off in about 30 seconds.

The jig took about five minutes to build. I used a 1-1/2 HP router and milled down 1/128" at a time (half way inbetween the smallest marks on my depth gauge). This was suprising quick as each head only took a few minutes. I probably spent 30 minutes total on milling the flats, including head scratching (no pun intended).

Corvair Engine Conversion

The next step was to replace the cast iron valve guides with bronze. Since my wife wasn't home, I took the heads to the house and heated them in the oven. I made a drift on the lathe to hammer out the guides and after heating for 30 minutes at 450 degrees, I tried to drive out the guides.

Corvair Engine Conversion

Based on what I found on the internet, the guides are driven out toward the cylinder side and new ones installed from the cylinder side toward the rockers. The new ones come from the freezer and are greased prior to installation. So I would heat the head, dive out a guide, and put the head back in the oven for a few minutes. Whoever though that driving these things out with a hammer was acceptable was off his nut. The did come out, but I though the force required was a bit excessive. And all it would take is one misplaced blow and I'm sure something would crack.

After I got 6 guides out and 2 and a half guides in, I stopped.

I retreated to the shop since I have better tools there. I set up my kerosene heater and warmed up the heads again. Whichever part of the head was in front of the heater got about 250 degrees. The heads took turns either sitting in front of the heater or being worked on. Although the oven at home got them much hotter, this way was much more shop friendly.

Corvair Engine Conversion

Being hesitant to really beat the guides in, I tried an air hammer to set the guides... nothing happened. Ultimately, beating it with a hammer was the way to go and I was able to set all 12 of the guides. My recommendation is to use lots of grease and oil, work on a block of wood large enough not to bounce around, and use a two pound hammer. So now I know why some builders recommend to leave the original cast iron guides in.

The next step was to ream the guides. I used a standard 11/32" chucking reamer and a drill. It's pretty difficult to get the reamer straight at first and it takes a delicate hand. I did not do a perfect job, but they were all acceptable expect for one. I ultimately replaced that guide and tried again.

With the guides reamed, I ground the seats... actually, I cut the seats using a Neway seat cutter. I simply used a 45 degree cutter, no 30/45/60 business, and so I selected a cutter that had only one angle (it was a little cheaper). I also bought a 11/32" cutter guide, but it was a little too large to fit my reamed holes. So, I made an undersized guide on the lathe, but it would have been easier to just initially pay the extra $25 and get the second guide. If I had to start from scratch, I would recommend getting the Neway cutter "CU608" and the two guides "140-11/32" and "140-11/32-1". I can't recommend one guide over the other since the standard guide may have worked if the tolerance of my reamer was on the high side. Also, the special Neway turning tool (essentially a handle) was not necessary... a long wall socket and socket wrench works just fine. Once these were cut, the valves and guides were lapped with lapping compound.

I lapped the heads using the setup pictured below. The fuel hose was slid on the exposed stem of the valve and the pulled while turning.

Corvair Engine Conversion

Using a method copied from Mark Langford, I installed "studs" to hold down the intake tubes. His plan includes drilling and tapping holes in the intake log and then to install studs (the "log" is the intake runner of the cylinder head that feeds the cylinders). The studs allows an intake tube to be bolted on as opposed to welded on after the carburetor boss is cut off. But since there isn't much aluminum material left on the log after milling the flat, a traditional stud would likely pull out. His method involves using a stud with a thin nut or washer welded on the end and then install the stud from the inside of the log. The welded on washer keeps the stud from pulling out. Since you can't get inside the log with a wrench to turn the stud, he had a stud that accepted an allen wrench so he could turn it from the outside.

Corvair Engine Conversion

I don't have a picture of it, but the first step was to measure, mark, and center punch the locations for the threaded holes. I use dial calipers to measure and then just drag the point of the calipers to scratch a mark. After I center punched on the scratch marks, I drilled and tapped the holes by hand.

My stud method is just a little different from Mark's. First, I took a 1" long 5/16" bolt (grade 5 and coarse thread) and thinned the head. This way, I didn't have to weld. The head was cut down to about 0.100" thick.

Corvair Engine Conversion

A 1" long bolt is too long so it needs to be shortened just enough so that it will slide into the log. I cut mine on a lathe but a ginder would work. While it was in the lathe, I drilled a 3/32" hole in the end about 1/8" deep (the photograph below is a "before" shot).

Corvair Engine Conversion

At this point, I made sure that the bolt turned in the threaded hole with no effort; it needs to thread in with finger force only since there won't be a lot of force that can be applied during installation. With the cylinder head sitting upright, the bolt was set in the log standing on its head.

Corvair Engine Conversion

I slid it under the threaded hole and hammered in a drill bit slightly larger than 3/32". I used the drill bit to pull up the bolt and turn it into the hole. Before it was all way up, I put some red threadlocker on the bolt, then screwed in the bolt the rest of the way. To finish the job, I pulled the drill bit out, double-nutted the stud, and tightened it with a wrench.

With all machining now done, the heads were given a good cleaning.

With the heads done, it's amazing how fast the installation goes from there. It's mostly a bunch of simple little tasks. Using a valve compressor loaned by the local parts store, the valves were installed. The spark plugs were installed. The head gaskets were coated with copper spray gasket sealer, but most some recommend putting them in dry. The studs were coated with antisieze and the heads were lightly pushed on with the top nuts only. Using assembly lube, the lifters were put in. Then the pushrod tubes were installed. The pushrod tube O-rings and anything that touched the O-rings were oiled first. The lower nuts, oiled on the outside and antisiezed on the threads were installed with the pushrod brackets in place and the little O-ring below.

I torqued the heads down in several steps, something like 15, 20, 24, and then 25 foot pounds. I don't like to make the last step a big one since as you torqe down a group of fasteners, the one you are working on changes the torque value of the previous one. I like to minimize this by making one final small step. I also used 25 foot pounds, which is about 75% of the recommended unlubricated value of 32-34 foot pounds. And, because I made the rookie error of not installing the pushrod brackets correctly, I got to torque it down twice. Those little brackets under the lower studs face only one way, otherwise the pushrods don't go in.

Then the pushrods were dropped in, with the little hole pointing toward the rocker and assembly lube on the ends. The rockers were screwed down, again with assembly lube on the valve, rocker ball, and pushrod dimple. At this point, I just screwed down the rocker until is was almost touching, just so the pushrod wouldn't fall out of the center of the lifter.

Corvair Engine Conversion

After going warming up at home for a little while, I came back and tightened down the rockers. Tighten down until the rocker, valve, and pushrod touch and then 3/4 turn beyond that.

I bolted on the valve covers and MY HEADS WERE FINISHED!



I was anxious to see if my little starter would turn the engine so I built some brackets and welded them to my cover. The starter looks nice...

Corvair Engine Conversion

I hooked up jumper cables to my shop battery and THUNK, engine turns a little, and then nothing. What the hell, no oil in a tight engine and even a larger starter would have problems. It seems like failure is immenent with this starter, but I'll sure to try again.

Well, I tried again. I ditched the jumper cables and wired it up properly. With this, it turns continuously but pauses at the top of compressions. I then bolted the propeller on and the additional inertia of the propeller helps to swing it through the compression. So now it swings as fast and as smooth as any other aircraft engine. SUCCESS!

At this point, the little starter bracket I welded up has just about pulled free from the welds and the top cover is bent. This will be redesigned.

Corvair Engine Conversion

So I redesigned the cover, borrowed a friends CNC plasma cutter, and cut new brackets and a new top cover out of 3/16" steel. This should hold just fine, but I will probably have to rebuild the flying top cover out of alumimun to shave a few pounds. Currently, the top cover with brackets is seven pounds.

Corvair Engine Conversion

After a dozen "starts", the original bushing that positions the starter drive bent. I'm guessing that it was designed for a smaller engine. So I turned a new bushing on my lathe and simply designed it after the bushing on just about every other Mercury Marine starter, including those for the 200+ HP engines.

Corvair Engine Conversion

Because of this problem, I would suggest that the Mercury Marine starter from a 150 HP jet outboard be substituted for this one. It's the same starter with the stronger bushing. It also has a slightly different front end so a similar but modified mount would be needed.

HOLY SMOKE... not really, just regular smoke.

That starter failed. But I'm not sure if was because it was wrong for the application or if it simply was a cheap poor-quality rebuild. It never ran consistantly, strong one moment and weak the next, and it eventually had no power at all. I tore it apart and found all the windings shorted to each other.

So I got to try the other starter I was thinking of. For quality comparison sake, I did get it from a different supplier and it appeared to be a little cleaner, the drive wasn't as loose, and the little hole in the back was already tapped, just a few little things. Well, one big thing... it worked.

My guess was right, the two starters are identical except for the front plate and the drive return spring. The new one is on the right.

Corvair Engine Conversion

Below, you can see the two. The first starter (on top) would normally have a little black cover over the drive return spring. I would not recommend that starter since what's under that little black cover is a weaker return spring design.

Corvair Engine Conversion

At this point, I don't know if the second starter will make it on the final installation. I'm considering a rear starter setup. However, the second starter has successfully started the engine a dozen times with no problems. I wouldn't recommend against it, but since it hasn't really been fully flight tested, I can't recommend for it. It seems to be a nice little starter; time will tell.



To minimize fuel piping, particularly fuel piping running through the cockpit, my fuel system will not use a return line. The pump, filter, and regulator will be located adjacent to the tank and will be located in the wing. Only a single regulated 43.5 PSI fuel line will run from the wing to the engine.


My original planned layout started with a traditional layout: gravity from the tanks, to a fuel selector, to a gascolator on the firewall, with two low pressure pumps in series to... and opposed to a float bowl in a carb, a header tank on the firewall. This tank would have the same configuration as found on most motorcycles (submerged pump and regulator, the whole assembly in the tank with one high pressure line out). The great thing about this is a tall header tank could be used as a dirt sump, gascolator, and would assure that the pump never sucks air (transient air is removed with the overflow out of the top vent back to the primary tank since fuel is constantly circulated). Remember, a float bowl on a carb will stop the flow of fuel. When substituting a header tank for a float bowl, the fuel is not stopped and is in constant circulation out the vent/overflow back to the primary tank.

The first problem with this arrangement was venting this header tank. Since you have a pump filling it up, the overflow/vent needs to feed back to the selected tank. So now I would have to run an overflow back to a double or second fuel selector (one for fuel, one for the overflow) with overflow lines running from the selector to each tank. This way, as you draw from one tank you don't incorrectly transfer all the fuel to the other tank by means of the overflow. This gives four fuel lines through the cockpit plus the pair from the switch to the header. Of course, I had considered also connecting the right and left tanks with overflows and check valves to avoid the situation where fuel circulation was incorrectly transferring fuel to the inactive tank. But then I realized I now have at least six different fuel/overflow lines running through the cockpit with the active overflow path pressurized. Also this arrangement seemed like a nightmare as far as possible failures and fuel leaks.

The next progression was to simply remove the fuel selector switch and feed the header from only one wing tank and then transfer fuel from the other wing tank as needed. If laid out in a diagram, fuel would be transferred from the secondary tank, to the primary tank, to the header tank, each with a low pressure pump and an overflow. So now I'm at four lines through the cockpit and several fuel pumps.

The second issue with a header thank is that now there is a mildly pressurized fuel vessel on the firewall. This also puts a notable quantity of fuel adjacent to the engine; a real problem in a nose-in crash. The next progression was to simplify in an effort to reduce the madness. The header tank functionality was moved to the primary wing tank. All the high pressure equipment would be out there and a single fuel line would run from there to the engine. The right tank was chosen as the primary for balance since it will normally have more fuel and the pilot sits on the left side.

My total design is currently boiled down to:

The left tank (secondary) connects to a filter, to a low pressure pump, and then to a fuel line across the aircraft which refills the right tank (primary). A momentary switch on the console energizes the transfer pump. The fuel line is a braided hose with a coil of slack in each wing root. There is no return, accidental overflow dumps overboard from the right tank vent.

The right tank (primary) will have a sump or baffle to ensure the pump never pulls air. This feeds a 100 micron screen, the fuel pump, a 40 micron screen, the regulator (with discharge back to the tank), and then to a braided hose. This equipment is located together in the right wing. The hose is continuous from this point to the engine with a slack loop at the wing root and possibly the firewall.

Both fuel pumps will be protected by an oil pressure safety switch. The panel will have a momentary switch to override this safety to energize the EFI pump. Starting will be a two finger affair: push in the override, push in the starter button, let go of both when started.

I do not have a redundant fuel system. I may consider a second EFI fuel pump in parallel with the first, each with a check valve at their outlet.


The first step was to convert everything for AN fittings.

The fitting on the Harley throttle body uses a GM style quick connect (also called a spring connect, EFI hard tube connect, push on connect, whatever). This requires an adapter to convert to AN-6. I got mine from Summit; it's a Russell 640860.

Corvair Engine Conversion

I'm currently using a Chinese fuel pressure regulator found commonly on Ebay. Like most fuel regulators, it is a bypass type. This means the two high pressure taps are regulated by allowing the return tap to dump as much fluid as necessary to maintain the high pressure setting. Normally, one high pressure tap is connected to the end of a fuel rail or connected to a tee in the fuel line. The other high pressure tap normally has a gauge.

I took it apart to remove the barb fittings and install AN fittings. As you can see on the housing to the right, the high pressure ports are the two side ports (up and down in this picture), and the bypass is located on the end (to the right). The housing was tapped for 1/8" NPT but is was so full of thread locker or Chinese epoxy, I had to retap to clean them up.

The little barbed connection on the housing on the left is for a manifold connection. Since the manifold is under a vacuum, the pressure across the fuel injector increases as the manifold pressure decreases. This changes the flow rate of the injector. The port connects to the manifold and decreases fuel pressure as the manifold pressure decreases keeping thing even.

To keep the installation as simple as possible, I'll not use this port and compensate in the EFI fuel tables.

Corvair Engine Conversion

To minimize fittings, I removed the gauge and will use the regulator as the the tee in the fuel line. This is not a common installation, but it appears to be the cleanest installation for this setup. If I need to set the pressure of the regulator, I will need to disconnect the fuel line extending to the throttle body and temporarily connect a gauge. Besides, a gauge is pointless once the regulator is installed hidden in a wing next to the fuel tank.

Corvair Engine Conversion

My engine stand panel is coming along... I don't have the stand's fuel tank yet, but you can see the fuel pump (Walbro 393 with AN-6 fittings), the fuel filter (Russell 40 micron), and the regulator. I'll need to stick a 100 micron filter at the pickup in the tank and install a return line from the regulator back to the tank.

This setup is essentially what will be found in the aircraft immediately adjacent to the right wing tank. The left wing tank will be considered a secondary tank and will transfer to the right tank with a low pressure pump.

On the panel, you can also see the MegaSquirt controller, an oil pressure gauge, and the four switches, which are Master, Computer & Injectors, Fuel Pump, and Starter.

Corvair Engine Conversion


Here are a few photos of the running engine as it sits on the test stand:

Corvair Engine Conversion

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Corvair Engine Conversion


So it's not yet ready for flight. There are several things I need to adjust, lighten, tune, or otherwise complete so let me say it capital letters... IT HAS NOT YET FLOWN and because of this IT IS STILL AN EXPERIMENT!


I plan on cleaning things up before I put it on my plane, but I've got to build the plane now. This is why I'll be scooting this engine over in the corner of the workshop for a year or two where it will sit, unfinished, non-airworthy, and out of the way. When I get it ready for its final installation, there are a few things I'll need to finish:

So how much money have I spent so far? Here's the breakdown from my Master Checklist:

$ 150 Engine core
$2,600 Rebuilding and converting
$ 800 ECU, wiring harness, throttle body, fuel pump, regulator (total fuel system), distributor, coil, plug wires (total spark system)
$3,550 Total

Not too bad. But to be fair this did not include a second starter (I melted the first one), a second ring gear (I redesigned it), two other sets of heads (they had no dollar cost, but it's worth noting when considering future builds), a new lathe, a shop press, and a few other tools (I'll use 'em again but you can't ignore their costs). There is probably a few small items that I did not list, like oil, bolts, etc. This did not include a new cam, new lifters, or crank grinding since my original equipment was in pretty good condition. But this cost did include the cost of the alternator, battery, propeller hub, and propeller. To get it airworthy, I'll probably have to spend a few hundred bucks more replacing the top cover and oil pan, getting the alternator installed, replacing spark plug wires, rebuilding the wiring harness, etc. So I'm looking at an anticipated true firewall forward cost of about $4,500-$5,000.