I have had my 280 for about 6 months. Its a 2004.

I used to have a 2003 sherco 250cc, which had lots more torque for some reason.

Anyhow. Today a knocking down low got worse very quickly. Sounded like piston slap.

Took the top end off. No scratches or grit inside the barrel. Rings look ok. Small end bearing has a little amount of play if I twist the piston along the line of the small end. (it rocks). The conrod has a massive amount of play when rocked side to side in parrallel to the crank (towards each end). Verticaly there is no play. Im strongly guessing this is wear on the big end bearing ??

The noise is not uniform. It sounds like a lump of wood in a slow running tumble dryer. Gets worse at higher revs. When cold it didnt seem to make any noise.

I looked for the two bearings separate to the conrod, but it seems to come as a complete kit for 145 pounds !!. This seams very expensive to me. I have bought these bearings for different bikes before which didnt cost more than 25 pounds for the two.

Edited October 9, 201411 yr by dudz

Just watched this video .... http://www.youtube.com/watch?v=0Em0GiLSO70

Seems the side to side movement is normal. So it has to be rings I guess. Which would answer my my sherco had more compression too

side to side is normal ,push to one side and check for up and down ,,, if nothing you need to check piston to cylinder clearance , also check if any up and down on flywheel

You need to measure everything accurately and according to book. The noise you describe sounds like main bearings.

Hello, ride it until it doesn't go, take it to Behind Bars, say to Andy "it doesn't go" pick it up a week later, flash your card, bob's your uncle.

Done the bottom end on my 280 and the kit actually comes with the rod bottom end bearing and crank pin.little end bearing come's seperate at £16 and the mains (which are koyo on mine) are available anywhere,up to you but don't scrimp on quallity should you need to rebuild.

Some of GasGas bearings are to thier own spec as i found out on building the gear box , and big end. Should you need to re plate the cylinder,then Langcourts are the best ,and piston kit for mine was £130.00 Certainly wouldn't ride mine till it goes pop as if a part disintigrates it could damage the crank case .

Edited October 18, 201411 yr by shyted