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YZ 250 coolant leaking help

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I just bought a 2000 YZ250. Runs perfect, has the best of everything on it, new top end, bored, re-jetted, FMF powercore etc...

Anyways, got it home, rode it and noticed it had a couple small drips of coolant on the side of the engine. Upon further look, i noticed it was dripping down the head from the head bolts nuts. I pulled the plug and found no evidence of coolant in the cylinder, drained the crankcase oil and found no evidence of coolant in that. So, why would coolant be coming from there? Is there orings or copper washers that are needing replaced? It has very lo hours on the rebuild, so i'm at a loss. I know it's not the head gasket (oring).

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Not trying to be funny or anything but are you 100% sure all the nuts were torqued down correctly?

I'm sure the manual would suggest replacing the copper washers each time you do a rebuild. I doubt that's really necessary but have you checked to see how much they cost? Sometimes parts like that are surprisingly reasonable..........if they're pricey then I would recommend annealing your existing washers to soften them up (heat them with a blow torch until they glow red and allow them to cool naturally).

Lastly, have you checked to see if your head is flat? It doesn't matter how good the or-rings are if the head is warped.........

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There are 2 o rings, the inner prevents coolant from entering the cylinder, the outer stops coolant from seeping from the water jackets out to the external portion of the cylinder and head, you may want to go ahead and get a new set of o rings, I think I paid 6 dollars for both and replace or at least inspect.. I wouldn't reuse those o rings just to be safe!

Good Luck!

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^ +1 on this... Im willing to bet that your outter o-ring is leaking! Had the same issue after a rebuild with a brand new o-ring at the beginning of this season. I always keep a spare complete gasket set for my bikes in the garage just in case, so I replaced it and no more leak.

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To my shame I have to admit that I re use those o-rings as long as they don´t have any rough spots. I put them in with grease and when rebuilding feel around the rubber if they are still Ok to re use. But it is not an easy task to get the outer oring in again. If you got the material readily available use new ones saves you at least 10min.

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