what would be the reason to replace pistons

 

Well there could be several reasons, both performance and repair. From a performance standpoint they can increase or decrease the compression ratio, allowing the owner to either go turbo/SC or go high compression without FI. If the engine is being bored out to a higher displacement, larger pistons will be needed. They can also be lighter weight, allowing for faster and higher revs, and are usually stronger than stock for performance reasons.

From a repair standpoint, if you have a timing belt/chain/tensioner break and the pistons hit the valves, they could be damaged. They could be extremely corroded from not enough use, or they could be so gunked up with carbon that the combustion process does not happen correctly anymore, leading to detonation and excessive wear, or a piston ring could let loose, scoring cylinder wall and piston.

Generally in a gasoline engine, unless catastropic engine failure or something leading to it occurs, there is little/no reason to replace pistons except for performance modifications. In general, it takes hundreds of thousands (like 600k+) for pistons to actually be worn out of tolerance specs.

 

Thanks for the reply. I find that very interesting.

 

Thanks for the reply. I find that very interesting and informative.