Originally Posted by GMSchmidt
Well, I wish I knew for sure. I'm pretty sure it was because of wrong head clearance. When I got the motor and ran 30% Sidewinder in it, I put one head shim in to raise it up. It ran great for 1 gallon and looked new inside.
Rigth before the Nats I switched to a different fuel that was 25% and figured it was OK to remove that shim. Well, maybe it wasn't. My pit guy and I were fairly confident that it wasn't lean (but it was so noisy it was hard to tell). I went out on the track and blew a plug. Brought it back in and put a new plug in. Went out on the track and the motor went to crap. When I pulled it in and torn down the motor to see what was wrong, it was clear. The plug was trashed and the piston had a major gouge in the back side (by the exhause port).
I really need to learn the proper way to check deck height. Because guessing and trashing a $600 motor really sucks.
Maybe you are running too hot of plug or you did have too much compression and it was detonating. Either one can cause detonation and it will make all kinds of noise. Will burn plugs up too.
One thing is for sure, the gouge in the piston is not from deck height, it was the broken plug element that wedged between the piston and the exhaust port. I've had one completely snap a con-rod and piston this way before. That platinum element causes all kinds of damage. Hotter plugs tend to burn the element loose easier. I prefer to decrease the head shim and run a colder plug instead of running hot plugs.