Hey guys &gals. I just built a motor about 600 miles ago,The motor ran great. But i used this motor in my race car so i am sure that had a lot to do w/it. The motor is an l28e. It will turn 8000 rpm,s very quickly, I know it broke the piston today. BUT WHAT I DONT KNOW IS HOW. Acouple of weeks ago the #3 piston hit the spark plug and closed the gap. I put a new one in it and there was a little bit of a rattle an then it cleared up with no problems. (I did check the cyl. for trash and there was none) well today it started again but this time it was #6. I changed the plug and ran it up the road and it ran fine. but when i got off of it, sure enough it done it againbut this time it moved back to #3.There was no rattles or knocks it just started missing. so i took all of the plugs out because they are the long shank plugs. and i put some short shank plugs in to give them some more clearance. Then i took it up the road, and it ran fine. So i stopped, pulled over and turned around. When i started moving again , it started to miss and then she started smoking real bad, so i am assuming that the piston broke. What i want to know is how come it kept swapping cyl., and how come it did not hit he plugs every single time i cranked the engine if it was a clearance issue? Any help would be greatly appreaciated. I just dont want to make the same mistake again. THANKS Gene.

There is at least one engine builder on the site who could easily answer your question. Haven't seen him post in a while. I'll give your post a bump.

I've only rebuilt a few engines and have always built them for street use. Never got to try anything wild.

My first guess is that you had plug interference on more than #3 cyl. Dome cracked and in time failed. You might find that more than one piston got "stamped". Try using some clay and reassemble head/block to verify this. Stressed parts don't do well when notched.

How much clearance did you have with the deck? I imagine the head was milled to increase CR?? Forged pistons or cast? Forged might tilt just enough when running cold to take one side up a few thous and if the clearances were too close...

Just pulling at straws.

Bump

Jim

I'm no expert on motor builds, but I suspect a number of factors could be in play. If your engine's clearances were marginal to begin with, thermal expansion & rod stretch at 8000 rpm could create a contact issue where there may be none at idle. Crank deflection at high RPM might be a possibility too. We're only talking a couple thousandths, but like I said, if it was borderline to begin with it may be the case.

You pull the head yet?