When is it time for new piston/sleeve?

[rocco79]

So the piston should never be able to pass through the top of the sleeve? I've never heard that before.

You never have? Yes, if the piston can make it almost to the top (1-2mm) without very much resistance . Your engine is cashed.... Now if you can get the piston PASTED the top of the sleeve you surely need a rebuild! Engines work off of taper and a very tight fit... If you can push it up that far when the engine is cold imagine how big the tolerances grow at operating temps.