How to tell if top end needs to be rebuilt? XR600

Just got the engine out to paint the frame. How could i tell that the rockers need to be replaced? Valves, camshaft, piston, rings, camchains, etc... have service limits. I don't want to splurge if it doesn't need to be replaced. I don't know the mileage or hours on the engine. How many miles should a cam chain last in normal driving conditions? Thanks!

Have you had any running issues? We have a '96 XR600 in the family, that is now a 629. It started running funny, before it stopped running. We did a compression test, and it failed.

We dug in and found the valves & seats where pretty badly pitted. So he had a valve job done on it. New valves & springs. Then he had the cylinder wall checked, and although it was still in spec, he had it bored to a 629.

To make a long story short, we get it all back together, and it still had running issues. so we started looking again, and finally figured out the auto-decompresser cam was loose. That was the cause of the pitted valves, and the bad running in the first place. He simply had the decompresser cam removed, plugged the oil hole for it, and the bike runs flawlessly now, and believe it or not, starts easier than it ever did new.

I'm told the stock valve springs are too weak for that bike, and the decompresser cam can be a problematic part. If those are stock, is may be good for you to have the top end re-done. My guess is 300 bucks or less for the whole job, valves, springs, machining, and I would have the decompresser removed before you have an issue.

I am in the process of rebuilding my head and installing new rings. I have received great service from Travis_37 when I did the head on my KTM so I plan on sending him the head to my XR as well.

I will take a close look at the decompression and valve to make sure this is not happening with my bike. the bike runs fine, but it burns some oil so I thought now would be a good time to rebuild it all and make it right.

The bike runs fine, but it burns some oil so I thought now would be a good time to rebuild it all and make it right.

If it's burning a little oil, it's probably some warn rings. If you have the money, and it's not going to hurt too much, I would go ahead and have the valves done. It may not even need new valves, maybe they just need to be re-surfaced. I would 100% do new valve springs.

With the decomp cam, it was pressed onto the cam shaft on my cousin's '96. Some how, the decomp cam became loose on the shaft, and was opening that exhaust valve at the wrong time. I think this issue had been getting worse for awhile. Like I said, he had a guy remove the decomp cam, and plugged it's oil hole on the shaft. You'll have to 100% use the manual decomp lever to start it, but we always had to anyways.

I believe his bike has been having that issue for at least a few years. It's possible it was a little out of wack from the factory.

I really don't know how common that issue is, but the decomp cam on an XR650R is bolted on, not pressed.

It is probably easiest to pull off cover at the moment , since engine is out. You will be able to see any serious galling on rocker surfaces & cam. I'm sure there are specs on cam etc. BUT it's easier to buy an aftermarket cam, which has no auto decomp. I took mine off & regret not buying a new cam. I like the way it runs & starts without. I had a hard time feeling the TDC posisition for starting. Now without auto-decomp you will know TDC cause you cant kick it thru(rock hard)Very easy to find & thus much less wasted leg kicking! If you love it & plan on a long relationship, invest alittle now while its out. And dont go crazy on mods, unless your racing. My bud has a punched out 600 by a known shop from this site with a little more cam etc.. after 3 carbs, still wont idle 100% & is pipey. & maybe it's just me, but I'm not crazy about it in tight woods. My 600 feels pretty good stock with edelbrock & a good flowing quiet pipe.

I have a '94 XR650L with 10k on it and it was smoking really badly on startup, otherwise ran great. I had a valve job done, bored the cyl to 101mm and put in a new Wiseco piston upping the compression from 8.5-1 stock to 10.25-1. I just put about 150 miles on it yesterday and busted it open a bit. It flys now. I never really had an issue with power before but now it's smoother and probably 25% faster. The cam didn't appear to have much wear, as did the timing chain guides so I didn't touch them. As far as I'm concerned it's good for at least another 10k. I plan on riding this thing down Baja this summer.

10K on a 94 L I have 11K on my 03, still runs great:excuseme:

I had a '96 XR650L with over 20,000 on it and it was "done". The top end made all kinds of funny (unhealthy) noises.

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