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post #1 of 11 (permalink) Old Aug 19th, 2009, 11:46 am Thread Starter
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Trans rear seal leak question

'85 K-100, doing the spline lube thing , and I get to the point where I pull the swingarm and find that the rear seal of the transmission is leaking.

The tranny is fine aside from that, and I certainly don't want to split the case if I can help it, so.... Is it possible to replace the rear main seal (at the output shaft) without splitting the cases?

Yes, I have a Clymer's but all it says anything about is the front seal, which you do have to split the case to replace, and doesn't even mention the rear seal, even though it takes you through a whole rebuild.

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post #2 of 11 (permalink) Old Aug 20th, 2009, 10:14 am
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It is possible, and relatively easy, to replace the rear seal without splitting the covers.There is an oil seal behind the flywheel, but also a O-ring behing the center bolt so you will need both parts.On my K100RS only the O-ring was leaking but I replaced both anyhow.
You will need some way to block the flywheel to remove the big center nut,and some kind of clutch alignement tool to center the clutch when reinstalling it (Or very good eyes...) There is some posts on that here and there. Also the pressure plate has to go back in there the way it came out to keep it in balance, so mark it's position relative to the flywheel before you take it out.And depending on how much oil leaked you may need a new clutch plate.
I'm surprised Clymer does not have that in the manual, if you look under clutch there should be something there, they will show the O-ring, and once the clutch and flywheel are out you can see the seal.
Common problem on all K-Bikes....all the way to the new generation....! I will probably even do my 2003 k1200RS as prevention against an expensive oily clutch.....!

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post #3 of 11 (permalink) Old Aug 20th, 2009, 12:21 pm Thread Starter
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Yup, Clymer has everything for the rear main seal of the crankcase, as does ibmwr and everyone else, but not for the output shaft of the transmission, which is my problem.

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post #4 of 11 (permalink) Old Aug 20th, 2009, 2:44 pm
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Originally Posted by Librarian
Yup, Clymer has everything for the rear main seal of the crankcase, as does ibmwr and everyone else, but not for the output shaft of the transmission, which is my problem.
My memory has faded since I had everything in bits. But the oem CD suggests it's fairly easy peesy:

1. Use a seal puller if you have one.

2. Or punch a hole in the metal case, screw in a self tapping screw and lever seal out with a claw hammer/pincers.

3. Fit new seal lip facing inwards - they mention a slip-over sleeve which usually means a circular sleeve of shim metal to protect the seal lips from being damaged by a splined shaft, make sure it's true to the casting surface. I usually use a large socket and check seals are square with a vernier depth guage. On this one the housing depth may be about right to centralise it - but sorry I can't remember now. Before extracting the old seal, check how its outer surface aligns. Measure the depth of the housing and the seal to see if they pressed it in as far as it would go, or only as far as the outer face of the housing.

The biggest fiddle faddle is getting the boot at the drive shaft end to go back. I think after they've got oil on them the rubber expands and they won't go back as easy as they came out.

Clymer is not perfect, but it's pretty damn good. Combine with the oem CD manual and you probably have everything. Watch clymer on wiring, there are a few errors.



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Last edited by voxmagna; Aug 20th, 2009 at 2:50 pm.
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post #5 of 11 (permalink) Old Aug 20th, 2009, 2:49 pm Thread Starter
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Originally Posted by voxmagna
My memory has faded since I had everything in bits. But the oem CD suggests it's fairly easy peesy
Now that's the sort of encouragement I needed. Thanks! Now I'll proceed to wreck things in my own unique fashion.

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post #6 of 11 (permalink) Old Aug 20th, 2009, 2:56 pm
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Don't forget to top up the tranny oil level you lost during old seal extraction and new seal replacement!

That's the smelly stuff that could be running down your arm!



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post #7 of 11 (permalink) Old Aug 21st, 2009, 7:46 am Thread Starter
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Don't forget to top up the tranny oil level you lost during old seal extraction and new seal replacement!

That's the smelly stuff that could be running down your arm!

You don't know me very well: that smelly stuff running down my arm is certainly not transmission lube!

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post #8 of 11 (permalink) Old Aug 21st, 2009, 9:02 am
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Sorry got confused on the seals....! Must be that I always took the tranny out on my K100RS and R100GS to lube the input shaft splines. Not that easy to get at,but those splines have to be lubed on the older K-Bikes .You can shorten the workload by backing out the transmission just enough to lube the splines, but you would not be able to inspect them properly that way, and that should only be done on bikes when you are sure the splines are good(as in lubed frequently....!) Since you have the swingarm out, I would recommend that you keep digging all the way to the clutch.

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post #9 of 11 (permalink) Old Aug 23rd, 2009, 7:47 am Thread Starter
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OK, I'm down past the clutch to the rear main seal. When I got there the well was dry, i.e. no oil leaks and everything looked so good I almost cried.

So, Off came the nut holding on the flywheel, yank on it then shove back to expose the expendable o-ring, and uh-oh... all of a sudden I have crankcase oil coming out.

So the first question is: was this normal and nothing for me to worry about, or does it mean I have a problem?

Next question: the pressure plate and the springy dingus were painted with white marks like the Clymer book says they should be, but the flywheel was not. The whole thing was assembled with the two white marks 180 degrees apart. So, did someone screw up or do I have a perfectly balanced flywheel? BTW, it appears that this bike was never ridden: the clutch is nearly perfect and the manufacturing date on it is July of 1984.

Another question: the boot at the rear of the tranny (the one attached to the clutch lever) was torn and trans oil was leaking from there. Why was it not also leaking from the front where the clutch shaft comes out of the front of the trans? Is there a seal that I should check/replace before I put everything back together again? Edit: AHA! found the oil seal in the diagram, but the old question comes back: can I replace it without tearing apart the tranny?

Still another question: the book says to replace the six bolts holding the pressure plate to the flywheel every time you take the clutch apart. Is this really needed? Yes, I understand the new bolt on the end of the engine output shaft, since that is a special case, but these...?

Anything else I really really really should do before I sew up the patient?

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Last edited by Librarian; Aug 23rd, 2009 at 10:05 am.
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post #10 of 11 (permalink) Old Aug 23rd, 2009, 11:35 am
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I think you are doing all the right things here.....including spilling a bit of oil.....!

I don't know where the crankcase oil level is relative to the rear seal, but it is probably higher than the seals to keep them lubed, so no real problem if oil comes out when you take the flywheel out.

The clutch/pressure plate assembly is mounted with the marks 120 degrees apart so you do have a perfectly balanced clutch.

Oil in the booth.....that happened on my GS which had a similar arrangement to the K-Bike, I don't remember any problems in pulling and replacing the seal, but you should replace the booth, dirt in there=rough clutch action. Isn't there a piston in there that pushes on the clutch rod? that should be very clean and lubed before you reinstall it.

I don't remember replacing the pressure plate bolts, but that was many years ago......! The shop manual for my K1200RS does not say anything about replacing them and it is the same type of clutch.....don't know, certainly locktite but replacement..... Mind you they can't be very expensive, but they have to be the same exact type of bolts.

Do you have a clutch alignment tool?You can make one using a piece of wood dowel and electrical tape,but I have replaced many clutches on cars and bikes and never used one. If you do not have one you have to center the clutch by sight, looking through the center hole. Pretighten the pressure plate bolts just enough that the clutch plate stays in that position then slide the tranny in there. If it does not go in ,wiggle it a bit. The trick is to have the plate just loose enough that it centers itself.
Once that is done, delicately pull the tranny back and torque down the pressure plate.Push the tranny back in, bolt it down.....done
I hope this helps....

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