You can't measure piston clearance after the pistons have melted.

 

No piston didn't melt. Two broken pistons at ring land!

 

Don't you want to shoot for 12.6 for AFR on NA?

 

That's what happens right before the aluminum turns to liquid. It got hot enough to just fall apart.

 

research the broken #7 piston on hear and i am sure you will find all you need to know about why it broke. everyone seems to bust that one. either intake design or bad injector. you may have had an average of 12.8 afr, but those 2 cylinders and #7 especially had been runnin lean for a while. check in to a couple of those things and hopefully it wont happen again. a very costly fix to repair. good luck with it

 

Like I said earlier..., what REALLY gets me is one broke on top and one broke on bottom, but BOTH broke there the rings come together... That really is a BIG sign to me that there wasn't enough gap in the rings...

 

I ma sorry to see and hear this problem. I would assume there is too much piston ring gap. A gap too tight does not seem like it would cause excess heat, however it will bind in the cylinder wall. A gap too loose would cause too much heat from the pressure escaping. The funny thing to me is that the ring gaps are in the opposite places. The top ring gap on the drivers side pistons should be facing down. I wonder what the end gap was on these? If it was too tight you would more than likely see a score on the cylinder wall where the gap meets. Did an experienced builder set the gap? A piston gap on a larger bore is bigger than a piston gap on a smaller bore. I have heard many times of the #7 piston problem. I have always assumed this is to inadequate fuel. What was the engine? Was it NA, or boosted? If so what was the boost? Did you upgrade your fuel system?

 

I agree. In addition, the ring gap might have of been fine provided the conditions were normal. But if they got too hot, the gap closes and that's all she wrote. It looks as though the rings butted by the galling on the cylinder walls too. Right where the break occured in the 2nd picture.

 

From picture #2 & #3, I'd say the gap was too tight. BUT, it is hard to tell after damage like that and from a picture. Maybe 2 bad injectors? Waaay too much timing? How much timing was there at WOT? And did this happen at WOT? If it was detonation, there would have been severe hammering. The entire truck shaking from the engine trying to stop itself.

 

I don't see galling on the cyllinder walls. It looks like melted aluminum from the piston to me. Hard to tell from the pics.