Cr250 Jug


First time poster here, I've got an 04 cr that I picked up about a year ago in real good condition and let me tell you its a ripper. They guy I got it from said the bike scared him and it sat a lot and that he put a new top end on it shortly before selling.  It ran great for me all season putting about 65 hours of pretty hard woods riding on it and I recently decided to pull the head off and take a look and found this. Looks like some damage to the jug but theres still honing lines curving across it, what do y'all think?










I'm about to get a new top end for it forsure and I guess it needs replating? The rest looks ok but the mark looks kinda bad down by the exhaust port but I cant feel anything with a finger/fingernail. Any two stroke guys been here before?

Edited by MrChukles74

It needs a replate no ifs and buts, for future reference Id say 65 hours is too long between rebuild for a 250 let alone an inspection, IMO the damage you see is the result of piston slap . If you had done the top end 20-30 hours before that may have been all you needed .

does not look anything like piston slap to me, the damage is on the bridge and not both sides like slap would do.


piston slap will damage the intake and exhaust side, not just on the bridge.


I do say it need a new coating though.


hard to tell what might have caused the damage, maybe someone else might know.

Edited by Excitable

I wonder if it was a forged piston without the lubrication holes drilled any numbers on the piston? I think wiseco cr250 pistons start with an m

I'll be taking the head off this weekend I think, I'll give the piston a look around and see what I can't see.  Thanks for the input guys. And Millennium tech is a name I've heard thrown around here and theyre relatively close to me in the midwest so I'll probably send it up there.  

The bridge is a point of "weakness" we're there is very little material I would be willing to bet the intake and rest of exhaust side is also thinned outhowever the bridge being such a small area to begin with wore through first. If one lets the piston wear excessively it begins to be able to rotate on the wrist pin traveling at an angle to the cylinder this generates very high localized stresses on the intake and exhaust sides . In some case the piston binds up or cracks breaking off pieces before those stresses wear through the coating causing massive damage to everything. I consider him lucky that he checked up on it and all he did was wear through the coating.

Edited by Swes

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