Rear main seal leak??

[Filmcamera]

Hello,


The time has come to try and fix the leak I have from the engine to the clutch.


I changed the rear main seal less than 5 years ago and although I may have done it wrong a cursory inspection seems to show it as ok.


Before I install a new one I wanted to post a picture of the leak and see if there is possibly another reason apart from the rear main seal.


It might not be totally clear in the picture but there is a trickle of oil coming from the area just underneath the spline.

[Laitch]

There's an o-ring around that shaft that can leak. That's not uncommon. Outboard of that o-ring is its compression ring (9) and on top of the compression ring is the clutch nut (10). The o-ring can be removed with a curved pick. It's likely that in won't come out in one piece.

[Filmcamera]

Thanks, Laitch, I did manage to get it out in one piece but have ordered a new one just in case.


The question now is, do I replace the rear main seal again or hope it is just the o-ring?


Next job after this one is replacing the freeze plugs... that has me a little nervous.

[daveson]

Hi Filmcamera,

I'm guessing you noticed a leak from the bell housing drain hole, then the first thing you're thinking is, does it smell like gear oil or engine oil? I hope it won't be too controversial when I say that gear oil smells even worse than rotten cauliflower.

The next thing you're thinking is, if there's any oil stains on the clutch plate, that could be from the O-ring in front of the clutch basket, leaking. If the rear main seal leaks, that could just fall to the bottom of the bell housing from behind the clutch basket, and run out the drain hole. Then you're thinking, could a leak from the seal end up on the disc from all these parts spinning at high speed?

The next thing you're thinking is, do I want to go back in there again soon? Or do I want to replace both for peace of mind?

[Scott_]

One thing that I noticed when I did my 1st seal, as seen in your picture, if you fill the oil ABOVE the center dot in the sight glass, the level will be above the level of the lower lip on your seal the entire time the bike is parked. As seen it leaked out when you pulled the clutch basket off.
Look at your input shaft of the clutch basket to see the wear line of the seal.
If there is a slight groove, you will leak again.
3 options....
1-set the seal more proud of the housing so that the seal lip edge rides on a fresh area of the shaft, IIRC there was/is a TSB that says to set the seal about 1-2mm proud of the engine block to address this issue when replacing an original seal. Don't set it flush. Make sure you clean the shaft surface.
2-replace the basket so you have a fresh new input shaft, then it won't matter how deep you set your seal.
3-don't fill your engine oil above the center dot. It won't then set there and pool at the shaft for potential leakage when not running.

[Filmcamera]

It is engine oil for sure, not gear oil.


It got all over the clutch, so much so I started to get clutch slip, I have ordered a new one.


The last time I installed a rear main seal I did leave it slightly proud, maybe half a mil. I am pretty sure I am going to replace it, as Daveson says, I have come this far... when I do I will leave it further out.


I do see some wear on the exterior of the clutch basket, the inside looks OK but it is hard to tell.  I found a used one for $40 on ebay so I went ahead and ordered it, new they are over $400


I also ordered a new o-ring and a new compression ring.  Since I live in CR I won't get them for a few weeks but meanwhile I have lots of oil to clean up!

[daveson]

It was years ago that I removed the clutch basket but I think I remember that there was only a tiny amount of clearance between the back of the clutch basket and the engine casing. Some of the newer seals aren't as wide as the original, so then it might not need to sit proud.

You want to make sure that another clutch basket is identical to the original, I can see some potential problems. You want to make sure that there is clearance between the back of the clutch basket and the engine casing. You want to make sure that there is clearance between the clutch basket and the face of the seal. You want to make sure that the thrust washer clearance remains unchanged with the new clutch basket.

If the clutch basket isn't identical, here are some ways of measuring the thrust washer clearance:

https://www.k100-forum.com/t15958-how-to-understand-the-k100-engine-output-shaft

If not identical, it might be easier to just linish the shaft.

[Scott_]

FC, I pulled up the TSB for reference it's #2798(it's also available here on the forum). You were pretty close with your seal install.
The factory change went from .4mm recessed to .5mm(+.1mm) proud of the engine case. Basically a 1mm change in total.

[daveson]

If the thrust washer is much under 1 mm or doesn't look to be in good nick, it might be a good idea to replace it.

[Filmcamera]

Well, that hasn't gone well.

I installed the new rear main seal and the new clutch.

Everything seems to be buttoned up correctly and the gearbox went back no problem.

I can click the bike in and out of gear and the rear wheel spins freely in neutral and doesn't move if in first.

The issue is the clutch doesn't do anything.  It feels like the spring is fully compressed so pulling the clutch lever does nothing.

Not sure what I have done wrong.  I followed two different videos very carefully (Chris Harris being one of them) and have done this before with no issues.

This time however even tightening the clutch pack bolts I could tell something wasn't quite right.

Any suggestions?

[Laitch]

The issue is the clutch doesn't do anything.  It feels like the spring is fully compressed so pulling the clutch lever does nothing.

Does that mean the clutch hand lever can just moved back and forth with little effort?

[daveson]

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This time however even tightening the clutch pack bolts I could tell something wasn't quite right.

Any suggestions?

Are you sure the guide pins (or location dowels or whatever the proper terminology is) were in line with their holes before you tightened the clutch bolts?

[Laitch]

If the spring feels compressed, perhaps the clutch disc was mounted with its hub extending toward the engine rather than the transmission. The Haynes manual's troubleshooting section mentions this assembly error as one of the common causes of clutch malfunction. Distraction can happen. 

[Filmcamera]

I did triple check, I have the clutch mounted with the hub (the longer end) pointing out towards the gearbox, that is right, I think.

[The Mighty Gryphon]

Is the clutch rod installed correctly?  It sounds like it might not.  I think there is a difference between the K75 and the K100 in the rod and how it is assembled.  Before or after the transmission is installed depending on the engine if my bad memory is correct.

[Laitch]

Everything seems to be buttoned up correctly and the gearbox went back no problem.

This time however even tightening the clutch pack bolts I could tell something wasn't quite right.

In the quote above, the two sentences are in disagreement. When a procedure doesn't feel right, that usually is considered a problem. Complete disassembly to the starting point will probably be necessary.
In Reply #10 there was a question about the clutch hand lever. Perhaps the answer to it could give us a new clue.

[Filmcamera]

Yes, there is little or no resistance when pulling the clutch lever.

[daveson]

This time however even tightening the clutch pack bolts I could tell something wasn't quite right.

Any suggestions?

What does this mean. The bolts were harder than usual to torque, or easier or... If easier, I'm thinking about the possibility that the ring for the clutch basket has fallen out while it was moved around in the workshop. I was wondering whether to ask a question about the diaphragm spring, then I thought nah, better not. A bit of wishful thinking says to me, it would be good if all you need to do is adjust the clutch cable.

Not sure if the original clutch basket was replaced or the new one used.

[Laitch]

Yes, there is little or no resistance when pulling the clutch lever.

Is the transmission-mounted clutch lever moving when you pull the clutch hand lever?

[Filmcamera]

Yes it is, it just feels like all it is doing is compressing the spring in the boot, that the clutch rod is already all the way in.

[Laitch]

Have you observed that is what is happening?

[Filmcamera]

It is hard to see what is happening inside the boot but yes I have observed the arm moving and compressing the boot

[Laitch]

Which end of the clutch rod is contacting the diaphragm spring?

[Filmcamera]

The short end is up against the bearing which then has the spring pushing on that and is held in place by the boot cover.


The longer tapered end is against the diaphragm spring, except I am not sure it is actually touching it

[Laitch]

The clutch rod is oriented correctly. The tapered end enters the bushing in the output shaft; the shoulder of the tapered end bears against the spring. From your description the clutch cable isn't broken. I'm now wondering if this problem came with the replacement clutch housing. The K100 2V and the K100 4V model housings are the same; the K75 differs.
Maybe somebody here will come up with something else to check but disassembly, close inspection and measurement along the way is where I'd be heading.