Bought me a 18 XCW 300

Question

Bought me a 18 XCW 300 used a month ago and knew it had been raced a majority of its life. Still on the original piston after 70hrs made me wondered how long it lasted. Bike ran fine and pulled hard with the red auxiliary spring so wasn't terribly concerned. Broke into the top end today and found this… Haven't seen a piston do that but am sure it's been too many hours. I don't see any gouges in cylinder but also don't see any cross hatching. Should I get the cylinder replated? The bigger question is if that chip out of the piston could have fallen down in the bottom end or somehow made it past the rings and out the exhaust port. I can't find evidence of metal clanking around anywhere. What would you guys do? Replate and new piston rings and send her? Or can I get away with piston and rings.

Bought me a 18 XCW 300

Bought me a 18 XCW 300

Bought me a 18 XCW 300

Bought me a 18 XCW 300

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8 months 0 Answers 134 views 0

Answers ( No )

  1. Cant tell shit from your pictures. Other than what looks like a crack on the piston skirt, I dont see anything unusual. You mention the circlip was missing. You are lucky the wrist pin didn’t come out and wreck the cylinder more.

  2. Replace the piston and rings at the least…

  3. It’s a dirtbike, not a Ferrari. Give the barrel the fingernail test and pop a piston in

  4. This is why you don’t do a top end based on a compression test.

  5. Bore it and new piston, rings ,pin and clips better check that lower end and find out what happened to the chunk

  6. do the top end and ride it like you stole it

  7. Use a dial bore gauge to check the widest spot in the cylinder. Check that against factory specs. If the cylinder is out or has large taper, replate it. If not, get a new piston, and use a ball hone to lightly rehatch the cylinder surface.

  8. Pistons will crack like that when there’s excessive piston/bore clearance.

  9. I stripped mine down a few weeks ago

  10. Cracked both sides ran ok tho just a bit of a knock

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