Though pistons can often be salvaged when rebuilding or remanufacturing an engine, sometimes they have to be replaced. The original pistons may have worn or damaged ring grooves, wrist pins or skirts, or they may have cracks. New pistons may also be necessary if the cylinders have too much taper wear and the block has to be bored to oversize. Or, maybe you just don't want to reuse the original pistons if you're building a performance engine or a high load engine like a diesel light-duty pickup truck.

Piston Failure
Pistons can fail any number of ways. The worst kind of failure is a catastrophic explosion that spews shrapnel inside the engine. A cast piston can shatter like a grenade if it hits a valve at high rpm, or if a solid object is sucked into the combustion chamber. The underlying cause may have been a broken timing chain or belt, (a prime example of the need for preventive maintenance) or the head of a valve may have snapped off because of fatigue failure (which can be caused by a lack of concentricity between the valve guide and seat), or a valve keeper breaks off the top of the valve stem or it pulls through the spring retainer.

If your customer is driving with a performance engine, a close encounter between a valve and piston may occur if the engine overrevs causing the valves to float, or if a valve spring breaks.

Knock-Knock
Burned and broken pistons are another problem you'll often disc...