----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----Hello all....I think John Cooper may have hit upon something here....check your pushrods.....I had my shop pull 2 cylinders (1 and 3) to put on new seals to deal with oil leaks. We removed the piston pin so not to remove the piston from the cylinder. I was not present when it was reassembled. Runup was good, normal mag drops, flew the airplane, but it seemed a little weak on static rpm. A few days later at annual, I had no compression on # 3 cylinder and thought how could this be with a good runup and normal mag drop? How could the engine run smooth with a dead cylinder? And what has changed recently?
I then remembered that one pushrod, even though they look identical, is about a 1/16th
inch longer than the other, and sure enough, the shop had reversed them, which allowed
the intake valve to remain open a 1/16th of an inch when it should have been closed for the ignition stroke, thus no compression when the engine is not rotating. But with the other three firing, and at a higher rpm, # 3 was producing power but blowing past the intale valve. It ran, but you'd burn a valve quick like that, and I only found the mistake during that annual compression check with about a 1/4 hour run time since the error. I was lucky to find it so quickly. Even if you did'nt pull the pushrods during this maintenance, perhaps they should be checked. You don't have to pull the cylinder, just remove the rocker cover and rocker arms and you can pull them to check, if I remember correctly, it's been several years! Hope this helps, good luck!
Dan Hubly N415BZ 415-C
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