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czentner

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About czentner

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  1. czentner

    '90 CR250 Piston help

    Hi, Thanks for responding. I guess I am confused about the A, B, C D pistons, each labelled as for a STD bore. My bore is slightly out of spec, but still within service limits (FSM STD bore - 2.6138-2.6144, service limit 2.616), my bore is 2.6145 at its tightest. If I subtract 0.0020 (within the spec of the wall clearance) I end up with 2.6125 which when converted into mm is 66.3575, rounded to 66.36. Now, a prox 'A' piston is apparently 66.36mm ebay piston. I can find 66.35-66.40mm pistons labeled for STD bore online. Would this ProX piston work for my application?
  2. czentner

    '90 CR250 Piston help

    Hi guys, I am trying to restore a 1990 CR250 that I got from a guy in boxes. I got my cylinder mic'd and it checks out good. You can still see the crosshatching and this is what the machinist measured: Gauge set at 2.614 top: 0.0005 middle: 0.0008 bottom: 0.0005 FSM spec says standard bore is 2.6138-2.6144, service limit 2.616. So, good news right? It's within spec. What I don't know is how to calculate what size piston I need. FSM says standard piston OD is 2.6114-2.6122 and the cyl-to-piston clearance should be 0.0016-0.0030. Does this mean I take the tightest measurement of the cyl (2.6145) and subtract the min clearance (0.0016), and that should be my piston size? ie 2.6129? The piston that supposedly was in the bike has a lot of scoring on it and one of the rings was pinched - looking at the cyl they don't seem like the damage matches. Anyways, the piston has the following stamped on the top: STD 614PS CD Then an arrow. Any help would be appreciated!
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