91 xr600r bore kit

This is my first time posting here, and I was hoping to get some advice.

I have a 91 XR, last year I had to replace alot of the top end. I had the work done and the mechanic put over sized rings in it, but it still smokes pretty good. Theres no doubt it could use a bore kit, but I want to try to do the work myself and send the cylinder away. But I don't know what options I have. If someone could give me an idea of what I'm up against, or point me in a good direction it would be much appreciated.

First off, welcome to Thumpertalk.

The XR600 is fairly bulletproof. It must have a lot of miles or been neglected to need a rebuild. When does the bike smoke? If it smokes upon start-up, it is usually a sign of leaky valve stem seals. If it smokes after it has warmed up and upon acceleration, then it is usually rings. Too much oil can contribute to that as well, but that is not common. The XR's can wear the cam chain and tensioner, causing it to jump a tooth (or more) on the timing, which in turn can make the bike run poorly, or even not at all. If that does happen, you can have piston/valve interference.

Since you said you 'had' to replace top end parts, I would assume one of the above happened rather than you were just upgrading components.

Before tearing the motor apart again, check your compression and give us some details on the smoke.

An X girlfriends father used to own it, he sold it to a colleague and I bought it from him. After I got it home I ran it for about an hour, seemed alright, until I noticed a scraping noise when kicking it over. I brought it to a mechanic and he told me the oil pump had been clogged by excess black silicone used to seal the motor back together. He replaced the cam-shaft, rocker arms, timing chain, etc. He said when he put it back together with the old rings it smoked so bad that he went back in and put some over sized rings in it. It now smokes on start-up sometimes really bad, other times not so bad. Once it gets warm it smokes a little, but not even close to as bad as it sometimes does on start up. I got a shop manual for x-mas for it and have all the tools to to the compression test. I will try to get to that this afternoon and post my results. Thanks so much for taking the time to respond to my post! I really appreciate it.

Welcome to TT !!!

Was the valve seals replaced ? Was side play checked in valve guides ? Do you know how to check compression for worn ring diagnostic proceedure ?

I just got around to doing a compression test on the xr today. Not so good..... The bike was cold and the temp was cold (about 15-20 F) but I could only get 50psi out of it. I squirted a bunch of oil into the cylinder and it didnt help things. I can kick the bike over without the decompresor, which dosent seem right. I am planning on pulling the motor and bringing it inside. I want to do the work myself (with exception of a cylinder bore) maybe someone could point me in the right direction of what i'm getting myself into.

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