1986 XR600 blowing blue smoke

Hi guys:

My new (to me) XR600 is blowing blue smoke on hard acceleration. It smoked a lot when started after a four-month sit in the previous owner's garage, but looked good afterwards. Too bad I didn't look behind me when test riding it. Oh well.

Friends say it definitely puffs a cloud of blue smoke when whacking the throttle for a wheelie, and they're pretty sure there's no smoke after a sharp rolloff of the throttle.

Does this sound like rings? Valves? Valve seats? Is there an easy way to tell?

I found JAW's guide to replacing rings:


It doesn't seem too oppressive.

Thoughts? Opinions?


Yeah, that sounds like worn out rings to me. Worn valve guide oil seals will only smoke right after the bike is started, then it will stop. And it won't smoke when you hit the gas hard. However, if the rings are worn, it will smoke when you hit the gas, because you are increasing compression pressures and therefore blowing oil past the bad rings.

On an older air cooled bike, it's not too difficult to pull the cylinder and replace the rings. But you should for sure have the cylinder bored, and replace the piston with a matched up piston for the overbore. It's always a good idea to check/replace everything (do a complete top end job) any time you have it all apart.

After a new top end job is done, the bike MUST be broken in properly as if the engine is brand new.

My guess is that someone abused that engine and didnt keep the oil changed and/or didnt keep the air filter clean.

Good luck with it man, I know it's a lot of work to deal with, but it's worth it once it's rebuilt.

L.L. '00 XR650R street legal/ uncorked/jetted/ Fast Pig

'04 KX500 illegal/ crazy fast


my 86 did the same thing. i thought it was the valve seals till i took it apart. there was about 19 thousands between the piston and cylinder. smoked a little at idle and a lot when on the gas. so i would say go ahead and do the top end. i got my piston through here. best price i could find and great service!!! if you do your own wrenching it is very easy and economical. even with the wasted piston it had more power than i knew what to do with now i cant wait till it is fully broken in :thumbsup:

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