hello everyone,this is my first post so forgive me if it not done right.

i have a 1997 gasgas.today i noticed coolant leaking from a bolt holding the c/head on(h/gasket blown?),so i thought tthis was a good time to investigate a rattle which i have been putting off.After removing the head,i noticed that the piston has quite a lot of clearance in the bore,i measured the piston and it is almost ,35mm smaller than the bore.I`m giessing this is the cause of the rattle.Small end brgs and big ends are ok.Because i`m selling the bike in a few months i dont want to spend a fortune on a rebore, i`m guessing that`l cost about 200quid and i aint loaded.The bike is in good nick an runs really well and has bags of power.Any advice on whats the best option would be verry helpfull.

Edited March 5, 200620 yr by gasgasssser

How did you measure the cylinder and piston?

If you didn't use a micrometer and a bore gauge, you didn't get an accurate measurement.

You can get a pretty good idea of how much cylinder wear you have by checking the difference in ring gap between the bottom and middle of the cylinder.

hi,yes i used a bore gauge and a mike.do you know what the clearence between a piston and bore which are new should be?I`ve re measured and the piston is oval.I rekon i will be able to manage with a new piston

Edited December 18, 200520 yr by gasgasssser

When cold, pistons measure less across the gudgeon pins than they do front/back. I.E. they aren't round. But it should be round when hot. That's how they are designed.

Gasgasssser,

To answer you question

Do you know what the clearence between a piston and bore which are new should be?

I would advise that you check with your local dealer or Gas Gas but as a general rule for every 1" across the top of your piston you should have 0.001 clearance.

Im not 100% sure but Gas gas may supply oversize pistons to fit your bore with the correct clearance.

Good luck :hat:

Both of the above are correct.

Pistons are cam ground. They'd be cheaper if they were round!

.001"/inch is a good estimate if no specific info is available, but I imagine the stock spec and wear limits are available for your machine.