Originally Posted by Storydude1

Tolerances open up on sleeve/piston fit from expansion and any oil/grease in bearings flows easier.

I'm not saying preheating is good or bad, just wondering why everyone claims it is needed for longevity. If the motor NEEDS to be heated to reduce/eliminate damage when new, the pinch is too tight and the engine shouldn't have passed QC checks at the factory...IMHO. The Pinch is needed to produce compression due to the sleeve expanding more than the piston at operating temps. The "pinch" is more noticeable when new because the sleeve and piston must wear together, making a sealing surface.

I can see heating reducing the "felt" pinch, but I look at like breaking in a new dirt bile motor..Without a load placed upon the new piston and rings, it won't seal correctly and you'll have problems down the road. I know an ABC engine doesn't have rings, but the theory is the same...Without a load placed on the piston,. it won't wear in correctly.

Again, my opinion and worth what you paid.