What causes piston skirt wear?
 

Hi all.

My '83 TT600 piston wearing out on the piston skirt!! Replaced the sleeve with a 550's as 600 sleeve to expensive.but even with a 550 piston got same problem.a tapping sound starts from bout the second day of riding and just gets worse very quickly.Oil pump seems to be ok.Well,coming out of bleed screw,anyway. Advise or thoughts welcome,cause I really luv this bike and dont wanna sell!

Poor lubrication - or similar
It shouldn't have happened that quickly after a re-sleeve though!!!

Assuming that the sleeve had been bored correctly and the piston clearance was correct .
And that the engine had been broken in properly and not overheated [with the chance of a partial seizure ] .
I would look at the conrod and measure it accurately and check that it is not bent and that the small and big ends are parallel to one another .

How about checking the oilpump? Maybe low output?