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?

 

Way more information needed.

Is this a stock powertrain, or is there a turbo, aftermarket ECU, etc?

Was the engine smoking before it went kaboom?

Is the piston cracked all the way through? It’s odd that you say the rings look perfect. I can’t imagine how that’s true if the piston is now in two pieces.

What kind of maintenance history do you know about the car?