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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 28 Jul 2004
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valve stem seals..xtz660

ok..im now in greece on route to athens,my old faithfull xtz660, 53000kms ,is still pulling like a school boy,but it is chewing through the oil at about 1 litre every 1000kms.
fredxtz sugested that i ride the bike a bit harder at around 4500rpms(which seemed to defy logic in oil consumption) but it has for a short time cured the problem of my bike eating oil.(to some degree)
im going to get the bike compression tested first, and if that is fine i will have the valve seals replaced as im sure this is where the problems lie...

i was thinking i should also do the cam chain while ive got the motor open...is there ANYTHING else i should look into while im putting my bike in to get fixed.
any advice welcome, im putting the bike in to a mechanic in about four days time...
thanks again phil...anyone know a good mechanic in athens....
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  #2  
Old 28 Jul 2004
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Cam chain is a good idea.

If replacing the valve stem seals, you might as well de-coke the head & lap the valves in while it's apart.
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  #3  
Old 28 Jul 2004
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Hi Phil

The Yamaha camchain on this bike is an endless type. To change it means splitting the crankcases.

When you start a job like that where does it all lead to???, you only start to think about new bearings and seals during the rebuild etc

Do you really need to go that deep. A top end overhaul is much less work.


Ralph

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  #4  
Old 28 Jul 2004
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Naah, only removal of L/H (alternator cover) easy as ...... Good idea to replace camchain.

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  #5  
Old 28 Jul 2004
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Yes and no..
The operation is easy though complicated if you want to do well..
For example, when the mechanic will take off the alternator wheel he might use the "steel hammer" technique and hit like god of thunder on the crankshaft to make it loosen...this is not the best for crankshaft bearings, due to the fact its kind of hard to remove an old alternator wheel tightly fastened on it, they often do like this, then with a few kilometers it can result in other problems as failure of contecting rod, vibrations, ovalised cylinder, oil consumption..

If the mechanic is good and uses a special extractor to taka off the wheel...it's much better, only Yamaha mechanics "might" have that tool.

Also; in Greece, don't get fooled on the price by a small garage mechanic, they can be kind of sharky with tourists.

Good luck,

Mattias
France
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  #6  
Old 29 Jul 2004
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I would say leave the chain job until you get home as long as it's mot rattling. An easy way to check is to remove the chain spanner and check if it's at the end, but first remove the spring otherwise it will jump out of position. How many kilometers has the chain?
You cannot check compression on a 660 due to the automatic decompression built-in in the camshaft which only stops when the engine runs at more than 650 rpm if I remember correctly. You can take a leak test though. Works about the same, put pressure on the combustion chamber through the spark plug hole and see if it drops. But this will not tell you if your oil scraper ring is stuck in the groove. But then again, you should see blue smoke if this is the case. And if the bike is running ok and has enough power, probably the piston rings are ok.

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  #7  
Old 29 Jul 2004
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Sorry Phil, I never knew the chain would come out like that.

You learn something new every day.

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  #8  
Old 29 Jul 2004
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boys...thanks...im putting the bike into the mechanics tomorrow.im staying with a good friend who is greek and his brother has put me onto a bike mechanic.
so regarding the cam chain..theres no rattle so i guess if it aint broke dont fix it,the bike is still pulling hard and has been as faithfull as ever.
ill let you know how i get on,glad to see hundreds of xt600s in athens,very popular bike here.cheers,and thanks again..phil.
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  #9  
Old 31 Jul 2004
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Hi again Phil,

I was just reading on "equipping the bike" forum about K1N filters which seems to be a no good investement for a dirt bike.
I think also exhausts are not always a good investement, as they could damage valves; to much oxygen creates to much heat and seal will damage, so I think exhaust might be the guilty in your case, but I could be wrong.
Once I had a triumph with ducati exhausts and mechanic told me that the only good thing with it was the sound..the rest was only bad as lower power, more heat on valves, etc etc.
Do you have a non OEM exhaust?

Cheers,

Matt
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  #10  
Old 31 Jul 2004
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Another exhaust can in case of a 660 doesn't automatically mean that the engine gets too lean. Most probably it is still too rich, because the standard setting is much too rich. Mine even with a K&N and Laser exhaust without the Db-killer still needed the needle in the 2nd carb to be lowered!

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Old 3 Aug 2004
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sorry guys for my ingnorance on this subject, but why would increased exhaust gas flow from an aftermarket exhaust can tend to burn out my intake valve seals or any valve seals for that matter?.......
in regard to my bike...the verdict was worse than i thought,piston ect to be replaced.still dont know what the final verdict is...ill let you know how i get on.
phil....
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  #12  
Old 4 Aug 2004
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Aftermarket exhaust has no influence on the valve stem seals. Only on the mixture and exhaust gas flow.

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Fred, XTZ660, Holland.
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  #13  
Old 6 Aug 2004
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Hi,

Its a little more complicated than that..
The valves are in an engine among the most technical parts created(you could write an entire book just about them!).
It has to be/have:
1/ high thermical resistance(in NORMAL run condition an exhaust valve has a dark red colour...)
2/ high mechanical resistance(open/close +100 times a second!)
3/ lightest possible, to reduce weight forces, when it changes direction from up/down, GGeeee!!
4/etc etc..

We all know the valves change size when warm; they becomes longer, thats why you need a clearance to be sure they won't stay open...and COOL DOWN when closing correctly.

The exhaust gaz flow has the same temperature or less than the highest one inside the cylinder..(when you use bike as build by yamaha)

The OEM pipe is not empty and creates compression inside the exhaust as the gaz flows out the cylinder; let's say the exhaust is filled with burned gaz...

What happends when you put oxygen to a fire?
The valve "tail" will be affected!!

Valves have a maximum of thermical tolerance depending on the material they're made of..
above they'll burn(exhaust valves especially), above the "calories/heat" won't be evacuated properly but transmitted to pieces in contact with the valves..
Airplanes have valves filled with liquid sodium, to fly up there...
Ténéré's have valves made of a steel mixture.
Newer bikes have titanium valves; lighter; more rpm.

I won't say the lazer pipes etc are crap; they are performance products made for racing.
But they are not engine life products.
I think one wouldn't buy an exhaust if he wouldn't feel an improvement to the engine performance..


Gosh, that was hard in english!
I hope I explained "clearly" though.

Cheers,

Matt

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  #14  
Old 7 Aug 2004
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that was great... thanks very much for such a well thought out answer, now i see that my laser pipe is not such a good idea for overland travel...
so , i picked my bike up today from the mechanics and all is well(at least i hope).i got a first over size piston put in, rebore,ring kit,cam chain and sprockets and a new valve seals put through it aswell as a few spokes replaced on my rear wheel, plus a few other bit that are writen on the bill in greek...
total cost....680 euros..which i think was great. however i deaply regret not getting the clutch plates done at the same time...hmmm..
anyway lads, thanks for your help, i will let you know how she gets on.
any advice on running the motor in ie oil changes etc
cheers again...phil.

[This message has been edited by futronix (edited 06 August 2004).]
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  #15  
Old 7 Aug 2004
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The valve stem seals are not in contact with the gas flow, they are on the top of the cylinder head, near the top of the valve stem, which is not as strained as the valve disc. AND we are mostly talking about the inlet valve stem seals here, which cause invisible oil consumption because of the vacuum created by the engine. The exhaust valve stem seals do not get vacuum.
A Laser gives you less performance than a standard exhaust, unless you take the Db-killer out and change carb settings etc. It is mainly loved because it is fully made of stainless steel and muuuuch lighter [2,5 kgs. instead of a massive 6,5 for the standard].
The € 680 is a great bargain. And the Laser is good cause it won't fall off, and it makes more noise so it's safer. If you still have the Db-killer, take a big screwdriver. You won't regret it.
Where are you going now?

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