“I know all your tests” …..Well, maybe not all of them.


I got an email from a guy today saying he knew “all” of the testing I had done, a bit of a conclusion to jump to for a guy who has never met me, nor owns a copy of my manual.


The guy had a statement about cam gears, a subject I know pretty well, that was made as if I had never looked at them in the last 27 years. In reality, we do all kinds of testing, and a lot of it never reaches the point of being an interesting story. Less than a third of the testing we do becomes a story, but all of the data is integrated into the products and processes we promote.  On any subject on the Corvair engine, it is a good bet to say “ww probably looked at that, you could write him about it rather than jumping to a conclusion.” But people who jump to conclusions just want their opinion validated, and writing me isn’t guaranteed to do that.



Above, the underside of the 3,000 cc Corvair that has been flying on the Panther prototype for several years. Look closely at the front of the oil pan, in the cam gear section.  The silver part is a removable cover plate.  It allows the cam gear to be inspected on an assembled engine while it is still in the airframe. We made several of these oil pans during a period where we were evaluating different cam gears. Not all tests have been written about.



Look close: No, it isn’t Dan Wesemans Panther. This is Paul Salter’s. This plane will be at Oshkosh in a few weeks. It is getting the engine compartment finished. The 3,000 cc Prototype engine has moved to this airframe, and the prototype airframe has now been re-engined with Dan’s 3.3 liter stroker motor.




In the history of the modern Corvair flight engine, there have been just 3 broken cam gears, two of them on the same plane. These happened many years ago, and neither aircraft had substantial damage, both are still flying today. When considered against the great number of flying planes that didn’t have a cam gear issue, this isn’t a large number. Below are listed factors that builders should understand, these come directly from our processes and literature.


(1) When the crank is processed, it should have a new steel gear put on it.  All cranks, both billet and 8409 cranks processed by the Weseman’s all have new gears installed. Problems with cam gears often start with Crank gear issues.


(2) 10 years ago, we left crank gears in place when the cranks were nitrided. Although none of the 3 gear failures were attributable to this, we have not done this in many years. It is not as good as replacing the gear. Some builders who had their cranks nitrided at alternative shops failed to clean the gear teeth after the process. Inevitably this would cause someone’s cam gear to fail.


(3) Most crank shops never grind cranks that have gear driven cams.  They fail to remember, unlike chain or belt driven cams, there is almost no tolerance for eccentricity on the gear. You can take a crank that is ground perfectly straight when measured in Vee blocks, that will still have run out on the crank gear. This will produce two tight spots on the cam gear, and if the run out is bad enough, it will eventually cause a cam gear failure. All the cranks done by the Weseman’s are done by grinder who spends the extra time to zero in the crank before it is ground. This can be seen on assembly, as the gear backlash is uniform in all positions.


(4) Any prop strike is a cause for cam gear replacement. This may not have been the cause, but it is a common factor in 2 of the 3 previous cam gear failures. If you like to gamble, I can point to 6 people who prop struck a Corvair and then flew 200 more hours without replacing the cam gear.  Saving the hassle of pulling down the engine and the cost of a $70 gear is what they gained against the potential of a fatal accident. Place your bet as you like, just understand the wager on the table.


(5)  One of the comments forwarded to me included a note from Joe Goldman saying he was going to use a “delta” cam in his soon to fly plane. Delta is a budget cam grinder whose dubious claim to fame is regrinding cams without removing the original 50-year-old aluminum cam gear, allowing the builder to ‘save” $70. Although there are several of these flying, I have said for more than 10 years that this was a very bad idea for many reasons. I know Joe, he is a great guy, but that isn’t an endorsement of his decision-making on cam gears. Watch any conflict between money and known better practice, and you will see the moment when one person makes the statement ” It will be alright.” That is the moment the wager is laid on the table, and if they were actually 100% confident they were right, they wouldn’t hesitate nor verbalize their evaluation. But they do, and what you are witnessing is a persons laziness or cheapness overpower what they know to be right.  People almost always get away with this. Almost.




About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

6 Responses to “I know all your tests” …..Well, maybe not all of them.

  1. Patrick Panzera says:


    Only in the kindest way do I want to point out that this post needs several typo corrections.


    • Pat,
      thanks for the note, it is revised. Low on Coffee/headache/auto correct working off smart phone / having grease monkey self-edit leads to this.

  2. jaksno says:

    Being more than a dozen or so feet above ground is all the risk I want to take with my life. Everything else better keep working and money is cheap. Ever catch me doing otherwise, you have full permission to kick my butt. {;^)

  3. William,
    The original Sprint built by the designer Bill Spring flew with a direct drive Ea-81 Sube engine. My first list was the Sube list. They all seemed to use Delta cam and were happy. I was going to buy an ea-81 engine but moved to the corvair list following two of the leaders of the Sube list.
    When I used Delta I knew nothing of what they did or should be done with the cam gear. This was in 2006. I would have gone with your reccommendation if I did the cam, say in 2009. The crank in my engine was magnefluxed tested like new with 0 crank wear and fillets to new specs.
    Can’t wait to hear how the Stroker engine performs.

  4. Vern says:

    Same reason my new in the box OT-10 that has the loose thrust washer is now happliy cranking out torque in my 65 Monza car and not my aircraft engine. I bet that $70 “saved” in case of an aviation use engine failure is a lot less of a loss than the 6 o’clock new reports damage to General Aviation and especially in Experimental Aviation would be. Not to mention the pucker factor of a real off field engine out and possibly a lot worse! Thank you for pointing out the Nitriding does cause gear roughness, William. We have a standard “ampersand” 180Hp LM crank that probably will be used on our engine build, but even though it appears to be a good choice at this point it is still just a possible good core. I will leave the determination on the skills of the machinist recommended even though I am an experienced engine builder. Also great point on the machinist doing the grind must setup correctly assuring zero the crank centerline.
    Chains and belts allow..not gear to gear. The 3.3 does have all eyes looking. I can still move to that level on my engine and it may be the way we go as well.

  5. Amos Vinyard says:

    In my corner of aviation, when my troubleshooting skills fail, I am not too proud to call tech support or service engineering. We then work together to solve said issue. I’ve gotten callbacks from Pratt & Whitney’s Singapore office when everybody in Canada was asleep. Continental tech support is always available. When these guys speak, I can take their word on how to solve an issue even if it is counter to my opinion. Flycorvair runs the same kind of tech support. Limitless testing and around the clock availability, we all know you never sleep. We should ask questions, and then listen, because in your answers you never fail to give the history behind the reason for doing it the way you recommend. The conversations I have had with you always astound me with the specific details that you remember about parts, pieces, people and events. You are a indispensable resource, thank you for all you do.

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