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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 27 Jan 2006
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STARTED SMOKING !!

Hi, rebuilt my 3aj a couple of months ago(crank bearings,timing chain,rings,valve seals) bikes been running fine until the other day. it starts fine but requires some playing with the throttle to keep her running until she,s warm. on startup yesterday,after 30 seconds it just started pumping out blue smoke!! when its warmed up the smoke is not as bad,more of a slight haze. anyone got any ideas whats wrong? thanks T
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  #2  
Old 28 Jan 2006
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sounds like oil is getting past the piston rings and burning with the gas.If the rings are worn, not seated properly, or mismatched with the cylinder bore then this could be the problem.Also,if the engine was rebuilt with a break in lube of some type, then this might be the cause?
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  #3  
Old 29 Jan 2006
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found the problem,removed the rocker cover & had a look at the valve springs.one exhaust valve seal had come off the valve guide! (lesson to be learned here,make sure the seal is pushed all the way onto the guide!) T
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  #4  
Old 17 Jun 2006
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Gday Guys.
I apologise for digging up an old thread, but i've only just found this forum and my bike is misbehaving in a similar fashion to what is described above.
About 10 to 20 seconds or so after startup, my bike blows an amazingly bad amount of blue smoke from burning oil. The bike is a 2002 model XT600, which I bought brand new myself just over 3 years ago. At the moment, it only has about 14000kms on the clock.
A couple of weeks ago, I took the bike back to yamaha for a check-up and they confirmed my suspisions, that it seems to be a valve stem seal problem. They did a compression check also, which came back good (140psi), so that pretty much rules out the rings and bore as the cause of the problem (I hope!).
Once the initial smoke blowing is over, the bike runs as clean as a whistle and when i check the dipstick, it doesn't appear to be using much oil at all.
After reading Big T's last post, do you think it is possible that one of my valve stem seals has just popped up off of the valve guide???? If so, does the head need to be removed to remedy this?
Thanks in advance, Dan.
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  #5  
Old 18 Jun 2006
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unscrew the valve adjust covers , two round ones in the front and a larger one for the intake valves facing the rear. peek inside with a flashlight and one of those itty bitty dentists mirrors.. you should be able to see the seals
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  #6  
Old 19 Jun 2006
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Thanks Laromo.
That will give me something to do this weekend.
If I do find that one of the stem seals has come adrift from the valve guide, can it just be pushed back down easily into its place, or would I need to be removing the rocker gear and valve springs to get to it?
Thanks again, Dan.
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  #7  
Old 19 Jun 2006
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Hi Dan, think the reason my seal came off was because i used pattern ones, genuine yam ones are a far better fit. however i,m afraid it,ll be a head off job if you intend replacing them! just an update on my 3aj,s smoking habit, i got the barrel professionally honed, rebuilt her(again) and it,s still smoking as bad as ever!!! i have now given up! anyone wanna buy it ? hope you find a cure & if so i,d like to know how. cheers T
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  #8  
Old 21 Jun 2006
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A little trick I have got away with before to avoid a complete head removal is to feed a load of soft rope into the plug hole (keeping hold of one end) and carefully turning the engine over till it goes solid, you can then compress the valve springs in place as the compressed rope stops the valves opening.
Once done turn the engine back a little bit so the rope can be pulled back out and job done.
I havn't done this with an XT yet but have done it with other engines with good results.
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  #9  
Old 22 Jun 2006
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Thanks Big T, Capt Haddock and everyone else for your replies.
Tonight I started stripping bits off of the motor for diagnosis purposes. This is what I found:
This is the Left hand side intake port:


As you can see, it is as clean as a whistle.

This is the Right hand side intake port:


As you can see, this is my problem!!!! As soon as i took off the rubber adaptor that bolts to the head to connect the carb, there was evidence of oil in there.
Today I wrote an e-mail to Yamaha Australia, telling them what has happened. I'm not going to touch the bike any more than this until I hear back from them, just incase i'm lucky enought that they offer to foot some of the repair bill, as the bike is still relatively new.
Failing that, I will be attempting the valve stem seal replacement myself.
That's an interesting Procedure (with the rope) you've just told us about Capt Haddock... Maybe I will give it a shot. It sure beats taking the head off. But what sort of tool do you use to compress the spring when the head is still bolted to the barrel?
Well, i'm happy that I know what is wrong with the bike now, especially the fact that I won't need to touch the bore/rings/piston.
Thanks for your help guys. I will keep you posted on how I go fixing it up.
Dan.
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  #10  
Old 23 Jun 2006
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Angry

Hi Guys,
This problem you speak off has had me f*&k'd for some time aswell. I had my cylinder on my 3aj honed which was still on STD and new rings installed, left head as it was, bear in mind she did not smoke at all before this, started her up and she puffed out a fair bit of smoke which cleared after a run.
Next day on start more smoke which had me worried, my first thought was my valve stem seals as i could see the intakes were rather wet, stripped my head down to find the seals to be inplace and holding the valve up no problem!
Anyway i put another head on, remeasured my ring gap and guess what, still the same after sitting over night.
I have done nearly 200ks and find the exhaust does smell of oil altho she seems to burn clean when hot!! HELP this is doing my head in.

Just a thought maybe the oil over night is leaking down from the oil tank and filling the crank case and on start up to much oil is thrown up the cylinder by the crank!!
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  #11  
Old 23 Jun 2006
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Talking Aiaiai

Looking at the pictures, in my experience the black (carbon) deposits in the Right hand intake channel are normal. When the engine runs there is always some "backfiring" into the intake ports due to valve overlap. The R/H channel is only cleaned by fresh mixture occasionally as opposed to the L/H side. On all my XT/TT6's this is the case. Unless the deposits have a very oil feel about them it is not what you are looking for.

There's two options:
1. If you have only the blue smoke just after startup, this indicates 'wetsumping', during standstill the oiltank has drained itself into the engine, the crankshaft splashes more oil onto the cilinder wall then necessary, which is (apparently) insufficiently removed by the oil scraper ring. After a while, levels in engine and oil tank have stabilised to normal levels so the crankshaft does not splash oil around anymore.
When this happens, the oil level, as measured in the correct way, should not drop significantly over time.
To solve this non-problem (IMHO); you can consider replacement of oil pump and of the check valve located in clutch cover. Another trick is, to use thicker oil: go to 20W50 iso 10W40. Also, make sure that the crankcase vent system is clean and open, and your oil level is not too high.
Come to think of this, you can test this diagnosis as follows: if you do your oil change anyway, your engine will be almost empty of oil, as well as the oil tank. Now, if you pour in the oil into the tank you are not able to put in the required 2,5 or 3 liters all at once, because the tank will overflow (BTW: there is therefore always oil in the engine, so much for the dry sump). Now, start the engine, as you would do anyway to get rid of the fresh oil in the tank to make room for more. Blue smoke -> diagnosis incorrect. No blue smoke -> diagnosis correct.

2. Blue smoke continues, also after running a while. Then, the only possible passages for oil into the combustion chamber and into the exhaust is along cilinder walls and valve seals. An indication that your engine is burning oil is of course a dropping oil level.

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  #12  
Old 23 Jun 2006
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Question

the last time i changed oil, the oil pump would not pick the oil up. the only way i could get it to pump oil up to the head was to pressurize the tank with an airline! then it worked fine. would this indicate a worn oil pump? i,ll try your suggestion Auke & see what happens. Cheers T.
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  #13  
Old 23 Jun 2006
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Gday Auke,
You have made some very good points in your post!
As I took the Right hand rubber intake runner off of the head on my bike, I instantly found oil in there, in liquid form. So at this point, my problem looks to be that particular valve stem seal (Fingers crossed).
Yamaha Australia wrote back to me, telling me that there have been no recalls for the XT600 whatsoever and no common occurances of this happening that they are aware of. Obviously they didn't offer to help either!
I've bought a replacement valve stem seal for the grand total cost of $8 aus and probably next weekend, myself and a friend of mine are going to replace it without taking the head off.
Hopefully your oil pump theory can help Big T out!
Cheers, Dan.
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  #14  
Old 23 Jun 2006
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Quote:
Originally Posted by aukeboss
Looking at the pictures, in my experience the black (carbon) deposits in the Right hand intake channel are normal. When the engine runs there is always some "backfiring" into the intake ports due to valve overlap. The R/H channel is only cleaned by fresh mixture occasionally as opposed to the L/H side. On all my XT/TT6's this is the case. Unless the deposits have a very oil feel about them it is not what you are looking for.
Sorry, I just picked this up...
I'm not sure about what you guys get overseas, but as far as I was aware, all Australian delivered TT / TTR600's had a single carb, which means that both ports would receive an equal amount of air/fuel mixture passing over them when the engine is running.
I will stand corrected if i'm wrong.


EDIT: I take this all back, the TTR600 does in fact have a dual carb setup like the XT....

Last edited by Aussie_Dan; 26 Jun 2006 at 23:29.
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  #15  
Old 24 Jun 2006
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All XT 600's in the UK have a dual carb setup with a slide on the right hand side and a CV on the left hand side, the CV side only starts opening when the slide is mostly open so effectively the left side port is closed at low throttle settings, not sure about TT/TTR.
Hope this explanation make some sense Aussie_Dan.
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