JP1234,
Typical OEM pistons are cast aluminum, which are low strength. To strengthen them, steel inserts are cast into them around the piston pin. Unfortunately, cast aluminum and steel have different coefficients of thermal expansions. So as the piston heats up, the cast aluminum and steel expand at different rates. Result? High thermal stresses occur between the cast aluminum and steel inserts and the metals eventually separate. Over time, the cycling induced high thermal stress causes fatigue cracks to develop in the piston and failure occurs.
Solution? Replace cast piston with forged high strength aluminum pistons which have no metal inserts cast into them. Forged pistons also run about 80F cooler and do not develop any internal thermal stresses. Forged pistons are competitively priced, readily available and offer long term trouble-free operation. After you crack a couple of cast pistons, and go through the expensive rebuild process (i.e. engine disassembly, cylinder re-surfacing or re-machining, reassembly, etc.) you become a believer. Many racers use forged aluminum pistons for a very good reason.
Best regards,
CJR