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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 10 Jan 2007
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Smile still smoking 2

a previous thread started by aussie dan , smoking on start up--turned out on mine to be the cylinder head studs needed re torqued after recent top end rebuild 1000 miles ago or so--bit like the old british bikes used to be.
havent had any more smoke probs since (500 miles) so there yea go ive quit smoking for the new year!
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  #2  
Old 11 Jan 2007
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Glad to hear that you got your machine sorted Franz.
Unfortunately my bike still has problems... It's now been sitting in my garage for nearly 3 months. I haven't even bothered to start it.
I will look at it again in 6 weeks or so, but I now believe that the bore may be glazed over... It's been run all of its life on semi-synthetic oil (as recommended by my yamaha dealer) and after speaking to a few people, i've been told that these big air-cooled thumpers are best run on plain old mineral oil, which allows the rings and bore to bed in and seal properly.
So, it might need to be honed, with a new set of rings and a change to mineral oil.
Will keep all you guys posted as to what happens anyway!
Cheers, Dan.
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  #3  
Old 16 Jan 2007
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Still smokin.........

Dan

I've been watching your thread with some sympathy.
I rebuilt an XT500 a few years ago after it seized up due to oil starvation.
I used genuine Yammie parts throughout. The rings arrived in an unsealed box but end gaps checked out OK and I buttoned the motor up.
It smoked like hell when I started it and didnt stop. Eventually the exhaust was wet with oil. It smoked worse on the overrun even while just revving it in neutral. I stripped the head off and the piston had a small pool of oil on it.
I had many experienced people look at the motor as I changed cylinder heads, then valve guides and valves all to no avail. I had that motor out three times in a week!

Eventually someone suggested I fit just the oil ring to the piston and check what happenes when the piston was inserted into the barrell. Well it fell right through. I ordered another set of rings from yamaha and the despite a sealed box the oil ring expander just wasnt expanding the oil rings sufficiently to even vaguely scrape the bore. I carefully opened up the expander to provide more tension and the problem was solved. I have noticed that the bike does smoke a bit on startup now and I have no doubt that my solution hasnt stood up to the test of time. I have ordered a set of Deves rings (5 piece oil ring) as I have had excellent service from them in an array of motors.

This may just throw some light on your problem. I studiously conduct the "mike" test on all oil rings I install now in honour of the guy who solved the problem. The oil ring on its own should support the weight of the piston in the bore.

Cheers

Gavin
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  #4  
Old 17 Jan 2007
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Thanks Gavin.
What you have just said could most definately be the problem that my bike is suffering from...
Just like your XT, all of my head is perfect. New valve stem seals and even had the 'suspect' valve guide replaced with a custom made bronze one. The only thing it really leaves is the rings & bore.
Thank god these engines are simple and easy to work on!
Like i said, i'll let you know what I find after I get back from my honeymoon in a month or so and I dust my bike off and drag it out of the shed!
Cheers, Dan.
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  #5  
Old 17 Jan 2007
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Thumbs up

very interesting gavin, i will try this test this weekend as my engine is already dismantled! where can i get those rings you mentioned?
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  #6  
Old 17 Jan 2007
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deves rings....

www.deves.com

I order them from a local agent.

Gavin
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  #7  
Old 22 Jan 2007
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Aussie dan: Have you ever bothered to measure the diameter of the bore properly ?

High milers or over zelous honing can take too much off the bore and original sized rings just wont have the spring in them to cope. Oversized rings will be necessary and available from Yamaha. Manually prizing open rings is a bad bodge and they will only close up again or cause even wear.

If oversized rings dont help (measure the bore first before fitting) then you may need a new bore fitted into the barrel.

A pool of oil on the piston means either your rings are leaking, valve seals are mush or cylinder head gasket is toast or not sealing properly.

You might want to get your hands on a cylinder leakage tester too.
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  #8  
Old 25 Jan 2007
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[quote=tedmagnum]Aussie dan: Have you ever bothered to measure the diameter of the bore properly ?
quote]
Gday Ted.
No, i haven't measured the bore up yet.
I bought the bike brand new in 2003 and its only done 15000kms, so i wouldn't consider it high mileage yet. I do suspect the rings have issues though (even though a compression test came up fine) because even after an oil change, the new oil becomes filthy from what looks to be carbon very quickly...
I got it out of the shed and started it last weekend after it had been sitting unused for nearly 3 months and to my surprise, it only blew a tiny amount of smoke when i gave the throttle a quick twist.
I'm going to put plain mineral oil in it and run it around for a few weeks to see if it makes any difference. If nothing changes and it continues to blow smoke, i will take the engine apart and get the barrel honed (hopefully it wont need to be bored to the first oversize) and replace the rings.
Wish me luck!
Cheers, Dan.
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  #9  
Old 25 Jan 2007
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2003 ! Whats the mileage ?

If a compression test is good then the rings will more than likely be fine.

You could try doing a compression test after letting the bike sit, and then drop a spoon of oil into the bore and then try.

If the rings arnt sealing properly, the second test will give a higher figure.
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  #10  
Old 25 Jan 2007
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Quote:
Originally Posted by tedmagnum
2003 ! Whats the mileage ?

If a compression test is good then the rings will more than likely be fine.

You could try doing a compression test after letting the bike sit, and then drop a spoon of oil into the bore and then try.

If the rings arnt sealing properly, the second test will give a higher figure.
You sound surprised Ted!! Yes it's a 2002 model (I bought it brand new in the beginning of 2003) and its only done 15000km which equates to less than 9500 miles......
Might have to try the oil in the bore compression test like you have said.
The filthy oil does tend to make me think the rings are knackered though, or perhaps that the semi-synth oil that the bike has been running since new has stopped the bore and rings from wearing in properly....
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  #11  
Old 29 Jan 2007
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Smoking XT

Dan

When I checked compression on my newly assembled "smoker" it checked out fine. Thats because the problem was with the oil ring which contributes nothing to compression. I would carefully measure the bore and piston bore clearances for all dimensional specs and do the Mike test on the oil ring. Also measure all rings before installing them. Just because they come out of a sealed box doesnt mean they are right! I have had a number of thumper motors use oil after a rebuild (altho they didnt smoke at startup or otherwise). They just needed a good run to get the rings to bed in even after having covered a few thousand KM's. The assembly procedure that I now use is to assemble the barrell, pistons and rings starting with all components dry and oil free. I wash the bore with hot soapy water first. I put about five drops of oil on my hands and assemble the rings on the piston, piston onto rod and finally stick the barrell on. No lashings of oil. When its all buttoned up I start the motor put on my lid and immediatly leave for a short ride. Come back and check for oil leaks etc. My moneys on a bad set of oil rings! ;>) I'll revisit my smoking XT once I finish my latest project which will have me worried if it doesnt smoke everytime at startup....a two stroke Suzuki GT750.

Gavin
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Old 29 Jan 2007
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If your certain the oils coming through the rings then like gav said, you may have put the oil ring on incorrectly. The splits in the rings need to be 180 apart on a 2 ring set up, 120 on a 3 ring etc etc.

oil ring doesnt aid compression but oil DOES !!

It maybe worth getting your bore honed and then replacing the rings again and bed them in properly. Only way to be sure of a proper seal really.

I cant remember, but if there are oil ways going through the barrel and the head, a missing o-ring or damaged head gasket could also seap oil, hence why a cylinder leakage test would show this up. Its basically just blowing compressed air into the barrel through the plug hole and listening for gargles, feeling air and also there are ones with guages on telling your the resistance, a little like a compression test.

Are you running the original rings and un-fiddled with barrel from before the rebuild ? If you are then i doubt its the rings leaking. I still reckon its that valve.

btw, theres an excelent workshop section on www.visordown.com. I suggest you post the FULL details on there too for a fresh outlook.
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Last edited by *Touring Ted*; 29 Jan 2007 at 22:20.
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  #13  
Old 29 Jan 2007
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Cheers Guys for the input once again.
We haven't dis-assembled the barrel / piston yet, so that is still as it came out of the factory. The only thing we have touched is the head. The head gasket and oil gallery seal are both new, so there are no problems there either.
As you have both said, i think my oil ring has a few issues!!!
Cheers, Dan.
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  #14  
Old 31 Jan 2007
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Angry

Well i tried the "Mike" test yesterday on my 3aj. removed the top two rings & inserted the piston in the barrel with just the oil ring on, seems to be sealing fine. even poured some oil into the bore & left it overnight to see if it leaked through but not a drop this morning! this leads me to believe that the smoking problem has to be something in the head. valves have been ground in & genuine valve seals have been fitted, so what the hell could be wrong? when i took the head off this time i found one head stud broken! would it be possible that the studs have stretched that much, that the head is not sealing to the barrel enough & oil i seeping into the bore? this is the biggest headache i,ve ever had with any bike!! cheers: T
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  #15  
Old 31 Jan 2007
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Quote:
Originally Posted by big t
Well i tried the "Mike" test yesterday on my 3aj. removed the top two rings & inserted the piston in the barrel with just the oil ring on, seems to be sealing fine. even poured some oil into the bore & left it overnight to see if it leaked through but not a drop this morning! this leads me to believe that the smoking problem has to be something in the head. valves have been ground in & genuine valve seals have been fitted, so what the hell could be wrong? when i took the head off this time i found one head stud broken! would it be possible that the studs have stretched that much, that the head is not sealing to the barrel enough & oil i seeping into the bore? this is the biggest headache iv'e ever had with any bike!! cheers: T
Head stud ? Snapped ?? If your talking about the 4 long studs (is 4 right?) that pass through the barrel and the head, then yes this is the probably cause. Your gasket wont be sealing properly and your well on the way to a warped head.

Get this sorted ASAP

Only then is it worth looking into the head for valve leaks.
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