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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 Jun 2016
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1989 US XT600 main shaft oil seal leak

Hi everyone!

I very much appreciate all of the advice in advance!

I have a 1989 XT600 kick start version with 37,000 miles on the clock. This is unreal for any bike! Motor has never been opened up.. unreal.. owner changed the oil every 2K miles, was very easy on the bike and never took it off road. Bike has great compression and runs like a clock... starts easy and has plenty of power... I would say that this bike is MUCH more reliable than the Honda Xl600 ...

The main work I did to the engine was to replace the left/right case gaskets as they were seeping... I also had to helicoil the oil filter cover screw as it was strpped... the engine was VERY clean inside from all the oil changes. No signs of any 5th gear chips or particles. I also changed the carb insulators, and all new oil seals.

Main issue I have is I have oil leaking out of the main shaft seal only at high RPM 75 MPH or more riding. if I just keep it in city streets no leaks. I did put in a new seal and it was leaking... thinking the new seal was bad.. I have had this happen in the past.... I put in another new seal... same thing leaking. Oil is all over the tire and runs down the swing arm.

Any ideas out there? I have never seen this happen and I have owned over 140 bikes in my days. I made sure the seal was installed level and flush with the case.

By the way.... the YSS shock for the XT600 is just FANTASTIC!!!! SO HAPPY with the performance... on a fast trail ride the control is just amazing. I also modified the front forks by welding 2 out of the 4 holes in the dampening rod shut. Then you add the progressive springs and you are set... no bottoming with about 5 lbs of air in each fork.

Thanks for the help!!!
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  #2  
Old 27 Jun 2016
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Since it only leaks at high RPM, it's probably caused by crankcase pressure.
Have you checked the engine breather for any restriction?
Are you using genuine oil seals?

Bob
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  #3  
Old 27 Jun 2016
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Thanks Bob!!!

Yes... using OEM shaft seal... I'm going to check the breather to make sure it is clear... that has to be it!!!

Another question...the bike runs to good yet I feel as if I should replace the valve seals. I have read here that oil will leak past the stem and cause carbon build up into the combustion chamber scoring the cylinder wall.

There is no smoke at start up at all yet I'm sure after 26 years and 37K miles it should be done..

What do you think?

thanks! Eric

Here is a shot of the bike after a good clean up and light restoration.. she was in great shape as always garaged.
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  #4  
Old 27 Jun 2016
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Nice bike
If there is no smoke on start-up then your valve seals are good. No point in replacing them.

Bob
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  #5  
Old 28 Jun 2016
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Thanks Bob!

That was the issue! The new YSS shock has the spring set higher in the shock structure where the breather hose connects to the air box. It partially restricts it when you sit on the bike as the spring compresses. When you take the bike off road and hit impacts the spring was closing the vent line fully causing oil to purge out of the main seal.

Problem solved and thanks again!

Eric
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  #6  
Old 28 Jun 2016
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140 bikes, and impressed by 37.000miles on a bike? You need to cover more miles on a single bike, haha.

I've seen 2-strokes go further without beeing opened.


Glad you got the bike sorted, it looks mint!. Keep and eye out for the leak, usually the seals can/will keep seeping a bit, once they've started to, whatever the reason was.
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  #7  
Old 28 Jun 2016
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Quote:
Originally Posted by Jens Eskildsen View Post
140 bikes, and impressed by 37.000miles on a bike? You need to cover more miles on a single bike, haha.

I've seen 2-strokes go further without beeing opened.


Glad you got the bike sorted, it looks mint!. Keep and eye out for the leak, usually the seals can/will keep seeping a bit, once they've started to, whatever the reason was.
Thanks for the advice!!! yes I will watch the seal... I can see once they leak they could continue even if they are new like in this case.

Yes... I have had too many bikes!!! Most of them just to look at then sell later on.

Now I just have two that I love... this XT600 and a KTM 500EXC The XT is really fun with the suspension updates and of course the motor is just great even with the stock exhaust.
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Old 28 Jun 2016
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Glad you found the problem.
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  #9  
Old 28 Jun 2016
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Thanks again Bob.. you nailed the issue right off the bat...!
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  #10  
Old 13 Sep 2016
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XT mainshaft leak update and jetting

Thanks SO much Bob and Jens!

Well you were correct! Once a seal starts to leak it will leak even with the pressure issue resolved. I corrected the breather line and the main shaft seal still leaked yet it was less.

New seal... no more leaks! Very interesting considering the old seal only had 25 miles on it.

One more question... the exhaust is stock as well as the air box. I did remove the rubber intake snorkel and there are some small holes drilled in the box by the original owner.

Jetting is stock at 125 main and 48 pilot. the bike runs just fine as is yet the cylinder head temp after a run is about 255 F. I would like to get that down a bit... would a 130 main on the primary carb be ok? I do not think I need to change the secondary carb... the TT600 uses a 135 main there and the XT has a 135.

The stock pilot is fine as going any higher will make it harder to start as it is too rich.. I had to turn the needle in to get it to start easier when hot.

Thanks for the advice!

Eric
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  #11  
Old 13 Sep 2016
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Sorry! TT has a 135 XT has a 130 secondary carb jet.
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  #12  
Old 14 Sep 2016
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Dont bother, leave the carbs alone. The bike will easely handle 255F.

IMO Jetting for cooler running is primarily a 2-stroke thing. I really dnt think you will notice a difference. The mainjets have very little effect when cruising around .

You could close some of the holes, or install the snorkel in the airbox, but I dont think you will see much difference.
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  #13  
Old 14 Sep 2016
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Thanks SO much Jens... yes.. I have read that these carbs can be so tricky. The bike runs so well now and starts so easy not worth any changes.

Cant thank you enough! by the way your analysis of the of that oil seal was brilliant. I asked many talented mechanics and machinists and they did not know about a leaking seal will continue to leak like this.

Thanks again!
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  #14  
Old 14 Sep 2016
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You won't be able to get the head temps down any farther than what it is , these aircooled pumpers run hot . My hi-comp version will hit 320F on longer trips in warm weather , but the normal motors normally hit 250-285F depending on ambient temp . An oil cooler will help a bit to keep the oil maybe 20 degrees cooler , don't think it's real important.
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  #15  
Old 14 Sep 2016
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Good input!

I'm just shocked on how reliable these XT's are. 38K miles and no engine noise at all at idle. Once you hit 2K in nuetral I can hear a light noise but that has to be normal. Granted the oil has been changed every 2K miles since new and the motor is like new clean inside due to it. He also never took it off road or ever put a lot of stress on it. Only thing I had to do was put in a heli coil on the oil filter cover screw as he had the cover off so many times! I do hear the main bearings can fail. You can test this by removing the timing cover exposing the crank end bolt. You can then see if it moves with end play.

I have to say this may be one of the best big singles of all time. I know for sure the honda 600 would not last this long.

Thanks again for the advice!... I'm just picky on set up and now have it just perfect
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countershaft, main shaft, oil leak, transmisson sproket


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