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

Builders:

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.

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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.

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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.

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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.

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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.

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(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.

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(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.

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(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.

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(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.

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(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.

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.ww.

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