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!!!

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

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.

Nice bike
If there is no smoke on start-up then your valve seals are good. No point in replacing them.

Bob

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

140 bikes, and impressed by 37.000miles on a bike? You need to cover more miles on a single bike, haha. :D

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.

Glad you found the problem.

Thanks again Bob.. you nailed the issue right off the bat...!

XT mainshaft leak update and jetting
 

Thanks SO much Bob and Jens! :D:D

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

Sorry! TT has a 135 XT has a 130 secondary carb jet.

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.

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!

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.

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:D

Thanks man, glad you sorted it out.

Theese bikes are bulletproof, mine will reach 170.000km next week. :scooter:

Hey jens,

Well I did check the play in the crankshaft and the crank is worn. I took the timing cover off and by moving the crank with a flat screwdriver you can see the movement and hear a clunk. Not good... time for new crank bearings. there also is a knock at mid RPM and a vibration at 70 mph with stock gearing.

This is a job i can do yet will need to install a new rod while I'm at it. I will have to send that out.. I did see a guy names Mr. Crankshaft.. will rebuild the crank for 170.

The interesting part is how to remove the cam chain sprocket on the left side so you can replace the bearing. Yamaha sells the left side as a full part only. May be the only way to go.

Thanks!!!

Eric

How I didn't come off, nobody will ever know but I got home from a ride a couple of days ago to find oil all over the rear tyre and swing arm. Eventually located oil leak source to a completely blown main shaft oil seal. As soon as the motor fires up , oil gushes out. So , I guess I have a bit of a problem! I can't see any breather blockages, so i can only assume the oil pump isn't pumping? I didn't feel or hear anything amiss when on the ride......Would a blocked filter cause such pressure.?

XT oil issue
 

The XT has a lot of oil pressure... make sure you do not overfill your oil tank. It is easy to do. If your seal is old then it just needed replacing. My breather was getting restricted as I was using an aftermarket shock and the stock hose was too short. A new hose fixed the issue. The seal is easy to replace with the bike on its side. Try that and make sure you have the right oil level.

Funny you should say that,! I left the sump plug out overnight and collected about 750mls. Just now I checked the dipstick and it was way over the high level, so I was able to test the oil pump with taking the bleed screw out. Plenty of oil was pumped out. So that's a relief. Went on to dig out the seal which to me was very soft and flexible - not at all like an oil seal should be. Hmm. Oh well, should have a new seal and oil filter fitted on Thursday. My bike is year 2000 with 70,000km, (the last 60k by me ).

Great!! Mine has 37K US miles on her and she needed all new bearings and a stock sized piston... she now runs like new.

Hi Esacco. I'm interested on that shock. Please, Can you share the yss code? I Need another help. Can you measure the stroke of the shock? Thanks a lot. Nice bike.

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shock
 

Hi there! The shock # is MZ506-395TRL-01-X

It is a little longer than the stock unit.... .25 inch or so. The stroke is the same as the stock or close to it. The difference is NIGHT AND DAY!!! You can literally FLY off road and jump off of 4 ft water bars without bottoming. The stock unit is totally worthless.

THey are VERY high quality and also can be rebuilt. Get it on Amazon for the best price.

Yeah!! Many thanks.

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