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Corvair conversion engines - cracked crank link
Morgans wrote: "Cal Vanize" wrote The article does indicate that the cranks were from engines in planes that were flying. That's the good news. But does that also mean that the engines need a teardown and inspection as part of every oil change? If you are running a conversion that is different from William's conversions, it could be a good idea. g If people take the time (yeah, lots of it) to read the whole article, you will notice a few things, and I will attempt to point out some of the more significant (to me) points. Biggest point. Do not use corvair engines outside of the recommended operating parameters. Some sub points. Biggest one, don't use longer prop extensions. Big time no-no. Others include, don't use heavy props, or hand carved props. Don't overstress the prop with some aerobatic maneuvers, or hard landings. Make sure the crank is properly ground. Oil systems must provide for consistent oil flow to all parts, at all times; stay away from two line cooler and filter systems. Use low RPMs and big props, rather than smaller props and higher RPMs. Avoid detonation, which is easy to let happen, if treated like an aircraft engine. Obey all points of his conversion manual. Nitrated cranks are a good way to add an extra margin of safety, when obeying the conversion manual, but the other examples that have followed the manual have been OK for long operational periods, even without the nitrated cranks. Avoid other's add ons, like extra bearing hubs, as they have not been tested. I am sure I missed some points, or miss stated some, but if you are using corvair power, it would be wise to investigate what this man has to say, and not take my word on it. I remember saying a long time ago, that I would feel better (or something like that) if a redrive was used to take the stress off of the crank. I think I will still stand by those words. Of course, It would need to be a properly researched and tested redrive, which at this time, does not exist. Good points all. The point that stood out most for me was the part about the crank from the engine that William built for his own demo 601. From the article: "This engine represents a standard installation, albeit one that was flown at its limits by Gus"... "showed stress fractures on both sides of the area in question." at 200 hours. "no nitride" Note with particuclar interest the phrase "represents a standard installation" regardless of how his pilot flew the plane (it was HIS pilot after all). The statement goes on to say that the engine "was flown at its limits" not beyond its limits. What William wrote is that an engine he purposefully built himself for his own 601 demo plane had a not insignificant crank issue. If he was following his own recommendations, why did he use a crank that wasn't treated? He may be the Corvair conversion expert, but I'd like to read an explanation as to why he wasn't following his own specs. I have read every word on William's web site. It would appear that he has done his homework and research. He may be the most credible source for Corvair conversion aircraft engines. But yet, this discrepency sticks out sorely. |
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