A chunck of my piston broke off in my freshly rebuilt 460 and melted in the cylinder. I have a CR of 9:1. The timing if set at 10 degrees and run 92 octane. They are TRW forged pistons with moly rings. Is this a defect in the piston or is the engine tuned wrong. I managed to scrape the melted chunks off the cylinder wall and honed it a litte. There is just a few not to deep scratches. Does anyone know how this happened so it don't do it again. Any help will be appreciated.

Bob

 

let me take a guess,, did the piece come from the area from the top of the piston and the first ring groove on the side??

 

Bigred,
Were you experiencing any (and I mean any) spark-knock? Were you pistons flat-tops or did they have a dome?

 

Yes, the chuck came from the top of the piston, where one of the dishes are. They are flat top piston and have dishes. There was some sort of tapping sound coming from the engine, but not too bad before it happened.

Bob

 

Red,
How long was that tapping going on?

 

It did it all the time. I thought it was just the rocker arms were adjusted to loose. There is about 2000 miles on the engine.

 

Don't know about anyone else, but that sounds like spark knock to me. Sounds like your timing was to advanced, or your vaccum advance is to...well, advanced. Only other thing to ask is, is your vaccum advance hooked up to the right vaccum port on your carburetor? If it's not, then you're giving vaccum to the advance all the time, possibly causing spark knock and a burnt piston.

TBirdGuy

"Stuck with a m*par, Settle for a ch*vy, Happy with a Ford!!!!"

 

Sounds like it could very well be spark knock to me.. Make sure your timing is correct, and that the advance in your distributor is not too much or set too loose. If you have a real light advance, you may very well be running full advance when you shouldnt be, causing spark knock.
Best of luck to you...

J/.c

1965 Ford Galaxie 500 (okay, so not quite a truck)
460/C6 transplant @ 389hp/491 lb.ft.
14.29@103.8, 13-14 mpg heheheheheh