hi there guys im wondering if anyone could give me any advice on what to do

my bike has an annoying rattling noise which seems to be coming from the top end. it had a +1.0mm rebore just under a year ago by a previous owner and was fitted with a wossner piston, which has always slapped from cold. i have taken the head off and attempted to measure the bore and got 56.97mm as my biggest reading but im guessing it is 57mm, bore looks nice and clean. but i had no feeler gauges to hand at the time. bike starts first kick every time without fail and pulls well through all gears

anyway back to the noise. on start up the piston slaps is the prominent noise from the engine, however there is a rattle which seems seperate.to the slapping in the background. the rattle is there at tickover, not so much on acceleration but very distinctive on de-acceleration however is seems seperate from the engine speed. its really annoying and difficult to explain. Any advice would be appreciated, thanks

Aye mitch " Small end roller bearing, whip the head off, twist the piston back and forth [ clockwise+-anti,] play should be minimal,

I canna see it being piston slap ,as its been bored, the rings can be noisy , ask airhead, his rattled like a snake, sumone had widened the exhaust port- and rings were snagging,,,

ok ive just ordered a new bearing and gaskets which will hopefully be here tomorrow, if so ill strip the top end down on saturday and ill post my findings on here. i just really want the rattling gone as im selling in a couple months and it really lets the bike down

ok.so ive stripped the top.end down and cant really find anything wrong with the little bearing so it must be the piston and bore. im replacing the bearing anyway and ill let you know how it goes. a create a problem for myselft tho, trying to be clever i thought i could remove the whole top.end as one, and forgot to drain the coolant. so now my crankcase has coolant in it

ok so top of piston measures 56.40mm and the bore measures 56.98 is this right or does it seem too small?

the top of the piston always measures less than the bottom ., because the top gets hottest and it's to allow for expansion. To check piston you should measure it at the bottom and compare to Yamaha specifications in the workshop manual

ooohh.well its back together now and sounds exactly the same