Motorcycle Engine Modifications

Depending on the bore:

It will assuredly increase the performance if done correctly

whether it decreases the lifetime depends a lot on what is actually done

But in general due to lower tolerances in the "field" than in the factory one usually gets a shorter lifespan from any rebuild, whether boring to increase performance or simply removing the worn portions for new rings.

Part of the equation for endurance is whether the increase in volume was done to accommodate higher compression -different goals frequently done at the same time. Increases in compression *can* reduce engine life, but once you are doing this work you either value the increase in performance above all else, or you are forced into these choices by wear already.

Boring an engine by itself should not shorten the life of the engine. But if other modifications are also made to increase power, the temptation to run the engine harder to take advantage of that extra power might shorten engine life.

What fun is a hot rod if you can't enjoy it?