A friend took apart a motor that was smoking pretty severely tonight. The #2 piston (factory 99 piston) was cracked across the center of it inline with the wrist pin. The rings appear to be in great shape, no signs of detonation, rod bearings look good and even the cylinder walls are fine. This happened on decel while on an offramp while exiting the expressway. Any thoughts on what might have caused this?

 

wow the only thing i can think of is maybe casting defect some void etc that weakend it pics would be cool

 

Thats ******* nuts. I also vote defective piston. Maybe it was helped along by high temps due to low timing #s?

 

Saw the exact same failure a few years ago -- happened to a stock '95 piston soon after boost was added. Split clean in two just as you described, with no other signs of distress.

 

I know its a cliche, but some pics would help out to see what happened.


Was the engine ever opened at all?

 

I cracked two stock pistons in two seperate instances when I was running nitrous. I suspected detonation or heat. I had no other engine damage.

 

I'll get some pictures some time this week when I make it over there. It was running forged rods with the stock pistons on the bottom end. This motor had been running fine under boost prior to this. Just a little weird that there's no other problems with it. I think we were hoping to see signs of detonation or at least something that would point to an exact reason for the failure.

 

Here's a picture.

 

Casting defect me thinks. High RPM offload decel should be a time of maximum wrist pin stress. Makes sense the defect in the casting went "dynamic" and split the piston during those conditions.