I'm measuring the top end of a well worn 200 pro but am getting a cylinder ID of 2.519" or 63.982 mm. I was expecting something about 0.0015" over 64 mm. Does anyone have specs on piston/ cylinder sizes for this model? The parts list shows B, C and D pistons but says nothing about size. Thanks!

You may need to call Jim Snell on that one (Rising Sun), hopefully he has something

I'm measuring the top end of a well worn 200 pro but am getting a cylinder ID of 2.519" or 63.982 mm. I was expecting something about 0.0015" over 64 mm. Does anyone have specs on piston/ cylinder sizes for this model? The parts list shows B, C and D pistons but says nothing about size. Thanks!

If you check the top of the piston crown, you'll see a letter (A,B,C and sometimes D). For a well worn cylinder, you can usually order the next larger size. For example, if you have an A piston, you would order the B piston as a replacement.

Check the cylinder, often on the base gasket sealing surface, and it also will have a letter to correspond to bore size.

Unless you are a master machinist (which you may be), because of the close tolerances involved (and the wide array of rider's measuring talent), it's probably a safer bet to order the replacement piston by letter/bore size rather than measured spec.'s.

Jon

After cleaning up the piston, I found it marked with 63.950 but no letters. This matches up well with my bore measurements. I don't see letters on the cylinder. A previous owner replaced the piston so could Vertex sell pistons direct without letters? Anyway, it is my buddy's bike and he is ordering through Lewisport so I passed the information on.

After cleaning up the piston, I found it marked with 63.950 but no letters. This matches up well with my bore measurements. I don't see letters on the cylinder. A previous owner replaced the piston so could Vertex sell pistons direct without letters? Anyway, it is my buddy's bike and he is ordering through Lewisport so I passed the information on.

Adrian at LewiSport will know what to do. I've measured piston/cylinder clearance at .0015/,0020" on the new bikes and I think the A/B/C/D difference is .05mm. They match the cylinders to the pistons at factory assembly to get the correct clearance as Trials engines are very closely fitted compared to other competition engines.

Cheers.

Jon

If you check the top of the piston crown, you'll see a letter (A,B,C and sometimes D). For a well worn cylinder, you can usually order the next larger size. For example, if you have an A piston, you would order the B piston as a replacement.

Jon

Ive got a "well worn" 200 cylinder from 2002. It has no letter marking on it, but I presume its an A. Fitted a new A piston last year, but it is ratteling a lot. I should actally put a B piston in there?

-Jan

I did a little more research. If you go to the Vertex catalog for the UK, they list GG200 pistons by sizes. The part numbers imply a letter but I don't know if that corresponds to the GG letters.

http://www.gb.vertexpistons.com/