Piston Check + Usd Fork Diagram Please

[steve1979]

Hi guys, i am thinking of giving my 307 a top end strip down and replace the rings small end bearing etc, how do you check the condition of the piston (ie is there a certain tolerance for the piston) someone told me a size but i can't remember it now, also i'm not sure where to use that size lol, i will recrute a fellow mechanic freind to help with the strip hopefully. I was told (fingers) on the piston can wear and snap off, how thick should they be?.

Also i have a leaking front fork seal, i have stripped normal forks in the past but never usd ones, i have been told these are quite difficult to do! does any one have a exploded diagram of how they come apart.

Any help would be much appreciated, thanks

Steve

[lee harris]

size is not important luv, at least in amsterdam...erm. The diameter is not really a problem but the piston will be oval. Check max diameter and compare at top and bottom to min diameter. If it is more than 0,05 mm, it will need replacing. Also when new, the clearance on a round piston to the nikasil bore is 0,035mm. If yours is more than 0,07mm it will rattle like buGg

Edited November 10, 2008 by Lee Harris

[steve1979]

Hi Lee,

thanks for your reply thats the info i'm after. I spoken to Chris from classictrial too who is very helpfull he has given me sizes to go on as well, when i changed the carb for the OKO i took the reed valve out and had a look down into the barrel and the side of the piston which did not look scored but until the head is off i wont know. I think the next step is to carefully lift the head and have a look, you never know though, with a 16 year old bike perhaps someone else has replaced the piston at sometime although i doubt it. At the cost of spares for these fantics i think after i'm married next year i'll start saving for a newer bike, although i would like to keep the fantic also as it's a great bike.