Gday Guys.
As you may remember, a few weeks ago I replaced one of the valve stem seals on my XT600 as it had been blowing smoke on startup. As a few of you predicted, this didn't fix the problem....
I'm now about to strip the bike down, with the aid of a factory service manual that i have, but i have one question:
Obviously when i go to replace the cam and hook up the cam chain i will need to see the mark on the crankshaft cam sprocket to make sure that it lines up with the pointer on the crankcase. All of the diagrams in the manual show this with the left hand side cover and the magneto removed. I want to try and avoid removing this cover and the magneto if i can help it, so is there a way that i can see when these marks line up without disassembling the whole left hand side of the motor? Are the marks viewable if you look down the cam chain hole in the left hand side of the head and barrel? Obviously i don't want to get this wrong....
Thanks in advance for your answers.
Sometimes the bike starts as clean as a whistle, other times it blows enough smoke to completely smoke out my driveway. It's very tempremental.
Hopefully we find something seriously wrong once we remove the head. One fella that i know through work once had a KLX650 that blew smoke like my bike is doing after having a full rebuild. After stripping the motor for a second time he found that one of the valve guides had a hairline crack in it. Perhaps this is what has happened to my XT??? I guess i will find out when it's in pieces!
Cheers, Dan.

Hi Dan, if your not removing the flywheel from the crank you won,t need to see the mark. just align the timing marks on the flywheel with the crankcase mark & slot the cam sprocket in with its marks lined up, then bolt it unto the cam. turn the engine over by hand a couple of times just to make sure though! i,ll be interested to know what you find as mine has the same problem! Cheers T

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big T

Thanks T.
Yesterday we removed the head, after discovering that there is actually a mark on the flywheel to tell us when the piston is at TDC.
The intake valve that i have been concerned about is now even wetter with oil than it was last time. This valve seems to have be slightly damaged on the end somehow, where the collets hold it together next to the valve springs. It was very tight and difficult to remove through the valve guide.
After inspection of the head and comparison between all 4 valves, it appears that the 'problem' valve hasn't been rotating as it should during operation. Perhaps this has caused it to wear in a funny way, or overheat and cause damage???
We can see marks on the head, underneath the other 3 'lower valve spring washers' which indicates that they are working correctly and rotating as they open and shut.
I will be ordering new parts through yamaha tomorrow and replacing that valve and it's valve guide.
We've got a feeling that oil is somehow getting down between the valve guide and the head when the engine is hot. This means that when I shut off the engine, all of the oil is dripping down onto the intake valve, and getting burnt the next time I start the bike.
Fingers crossed we're right and replacing the valve and valve guide fixes this problem.
I'll keep you posted as to what happens.
Cheers, Dan.

Well, I picked up the parts that i need from Yamaha this morning, including a new intake valve and a valve guide.
The head is now off having the guide replaced, so it will be interesting to see if they find anything obviously wrong as they remove the guide.
Should have it back by the end of the week, ready to put the bike back together on saturday. Will let you all know what happens and If it fixes the problem.
Cheers, Dan.

I got the exact same problem. about 7 out of 10 starts it will blow smoke on cold start up. Only sometimes it smokes when i start it in the afternoon to go home from work (ie 8 hrs since last ride) but any shorter intervalls and it never smokes. Also i have noticed the colder the atmosphere in the morning the more likely it is to smoke.
I have never done anything about fixing it beacuase it is only 10seconds at start up and the engine has had 71000km virtually trouble free, So i don't want to pull the top off too soon (i dont awnt to have to replace everything in their just yet)

I'm eager to see how you go

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Yamaha XT600 1988

Well guys, whilst my head was off at the Engineering shop they found a couple of things wrong with the troublesome inlet valveguide. It turns out that from the factory, yamaha have put the retainer clip on from the bottom of the guide, which left two distinct score marks along it. Then when it was pressed into the head, this obviously left score marks in the head.... This could quite possibly have been how the oil was making it down into the inlet port.
The other thing is that this particular valve guide was drilled off-centre. that's right, the hole wasn't in the dead centre of the valve guide...
Anyway, they had to bore out the valve guide hole to get rid of the score marks that Yamaha put there when they assebbled the thing, and then make up an oversized bronze valve guide.
After getting the head back we put it all back together and she started first time i hit the starter button. As the exhaust had quite a bit of oil in it from before the repairs, we expected it to blow a little bit of smoke upon startup, which it did.
It's done nearly 100kms now (over 4 separate days of riding) and it is still blowing smoke un startup.
My gut feeling tells me that i haven't solved this problem yet...
The bore looked perfect and a compression test came back at just over 140psi, so i doubt very much that the rings are the problem.
This has almost got me stumped...
Does anyone have any suggestions?
I have a bike that isn't even 4 years old, hasn't hit 15000kms yet and is giving me so much grief. There must be a problem somewhere, as it never blew smoke like that when I bought it new and rode it off the showroom floor....

If all oil from the tank drains to the engine through a slightly worn oil pump and / or check valve, you will have a lot of oil splasehd against the cilinder wall at startup. The piston rings will not cope sufficiently to avoid the smoking. After some time, when the oil circuit is balanced out, the oil level in the engine has dropped and the crankshaft does not splash oil around anymore and the smoking stops.
I did this suggestion already (another thread?) - worth checking after an oil change when you are certain there is no oil in the engine.

Auke

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Auke
http://aukemarieke.blogspot.com

Yes, I do remember you suggesting this Auke.
In the past I have checked the top tank after the bike has been sitting overnight and it was still full. So I assumed that it is not 'wet sumping'.
I will definately check it again though.
One other thing that i will try is disconnecting the crankcase breather from the airbox, to see if that makes any difference. The engine doesn't appear to be leaving any liquid oil in the airbox from blow-by, but It will rule out another thing that could be wrong. Obviously I will block off the hole in the airbox to make sure no un-filtered air gets in.
Cheers, Dan.

Hi Dan, i know how ya feel mate! have stripped mine three times now to try and cure this problem! not gonna give up though, she,ll be goin on the operating table next week!! i,ll keep you informed when something is found. cheers T

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big T

My engine is showing the same fault, i know it is not top end,recent unrelated work[broke head stud]had very careful inspection of guides ,valves,bore and rings little or no wear--so thanks for that auke
good advice--check valve--where is it? Bike is a mongrel makes ordering parts a little difficult 1vj chassis 2kf bottom end 3aj top end italion import
i think it was built for a purpose--

The checkvalve is inserted in the clutch (R/H) cover. If you remove this cover you will see a kind of seal at the bottom, there's a steel ball and a spring behind it.
Suggest also to check the oil pump, for that you need to remove the clutch and the pump itself.

BTW: as far as I know, the checkvalve is the same for all XT6 models.

Auke

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Auke
http://aukemarieke.blogspot.com

Thanks again will

keep yous informed franz

I got around to fitting a new clutch cover gasket,the oil tank is full--not wet sumping--but still smoking on startup,not as bad as before gasket--not nearly..goes really well always does , still a great bike.

Mine is still smoking... Haven't solved it yet, but as Mini_S_Man has experienced, its getting warmer where I live now and i've noticed that the smoking isn't as bad....
I'm gonna take the bike off the road and then around christmas time when i've got the money i will strip it down again, to have a good look at the piston and barrel.