im not reading my resume, dont look at it like that. I clutched for an Acat factory racer from 95~2000. I spent a lot of time in the Cat factory and we had shop room classes on piston wash and then we had to go out and "tune" the engine to put carbon on the piston in the amount the lead tech wanted. Al Shimpa the lead tech started off the class with no words, just stood there [to get our attention] looking at us and said "Carbon sticks to a hot piston" and then said "repeat after me"..."Carbon sticks to a hot piston" and us students had to say it out loud. Al got us to Chant it out loud "carbon sticks to a hot piston" that was how our class started off. Every time you look at a piston you say to yourself "carbon sticks to a hot piston" and now can ask the question, how hot was the piston? You can tell by how much carbon is on it and how much the carbon propagated towards the edge of the piston.
Our objective was to run a 440 for 35 minutes full throttle (taped to the bar) in a 14 mile loop on a lake and
average 104mph so that means the sled had to go 106mph at times to average 104mph and that meant "taped throttle open". When we blew an engine up, go back to the shop and pull out a top end from the crate, give the pistons to Al, put a new top end on and try not to blow up this time.
Top piston picture shows a piston that has not been heated enough to get carbon to propagate to the edge of the piston. The piston did not get hot from a lean condition.
The below piston picture is from my 872 after 800 miles with an AFR gage telling me im running average 12.4. The carbon has propagated to the edge of the piston but is thin on the edge. I have held that w.o.t for over a minute, loaded in fresh snow.
..............im going to put my head on the chopping block and declare your engine was not lean, not in the least. Im gonna take a guess and say the ring snagged and snapped off the top land width. The top land width is the thickness from the top of the piston to the roof of the ring groove.
Saying "lean" to me the speaker who uttered that is a liar.
Someone made me an offer for my 872 i could not refuse, so out it came. The 872 went out west and into a 174. The piston you see in the picture below, went right back into the 872 because there is nothing wrong with them. New wrist pin and needle bearing and that piston is still running today in the 872 out in WA.
AND to prove this even more, is my 872 had a 50/50 cylinder head but i ran it on 92 ethanol fuel and was able to do it because i had piggyback fuel injectors with a dobec controller and could control the fuel for every 1000 rpms. The point is the piston below has carbon on it because its running HOTTER than the piston in the top picture, but the piston below is NOT lean. It ran 12.4 average on AFR.
Miserwideopenmafia - sorry to see that kind of thing happen to you, but your engine was not lean, something happened to flick the piston material off and the root of the problem is something to do with the piston ring snagging the port or the port was modified to be able to impact the ring....its not fuel its a mechanical dimension problem.
"carbon sticks to a hot piston" and mister, your piston has little to no carbon on it, so it was not lean.
