December 1, 201015 yr I am re-building my 2003 Gas gas 250 txt pro and phoned GasGas uk for piston rings, I was told that they can no longer be supplied as there has been a change in the piston manufacturer and I would need a whole new piston kit at 120 quid. I had been looking at a Wossner kit on ebay for under 90 quid, they advertise it as a better replacement... is this true? they also say... and I quote "OE bore size is 72.47mm. Pistons available in 72.47mm, 72.48mm and 72.49mm. Please specify which is required when ordering." I have been told if I go for the middle size I will be OK but Wossner say I should take the barrel to an engineer to be measured (too much hassle) Any advise would be great. Thanks
December 1, 201015 yr I am re-building my 2003 Gas gas 250 txt pro and phoned GasGas uk for piston rings, I was told that they can no longer be supplied as there has been a change in the piston manufacturer and I would need a whole new piston kit at 120 quid. I had been looking at a Wossner kit on ebay for under 90 quid, they advertise it as a better replacement... is this true? they also say... and I quote "OE bore size is 72.47mm. Pistons available in 72.47mm, 72.48mm and 72.49mm. Please specify which is required when ordering." I have been told if I go for the middle size I will be OK but Wossner say I should take the barrel to an engineer to be measured (too much hassle) Any advise would be great. Thanks Check for markings on the piston you took out. There will sometimes be an "A", "B", "C" on the cylinder (sometimes on the base sealing surface) and/or piston. My guess is that the A-B-C corresponds to the sizes that Wossner offers. Generally you should be o.k. with the middle size on an 03' as there will be a little bore wear, but you will want to be as accurate as possible to get the best results. Jon
December 2, 201015 yr Author Hi Jon there is a "B" on the piston head, I am guessing that I am going to be safe with the middle size, thanks for the info Mike
December 2, 201015 yr Why guess when you can go & get the bore measured? This is the most important part of the engine!
December 2, 201015 yr Why guess when you can go & get the bore measured? This is the most important part of the engine! Hands-on measurement is always the best way and a dial-bore indicator will also give you a measurement of bore taper. Your "B" piston is undoubtedly the 72.48mm and a lot of riders opt for the "C" piston in a "B" cylinder that has 7+ years of use. Look for .0015-.002" clearance on the bottom cylinder bore to lower skirt (front to back) piston measurements. Ring end gap should be .1mm (.004") per inch of cylinder bore. Jon
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