Rear Main Seal seating

[Kentallen8]

Okay, I think I’ve exhausted my search options and have not come up with an answer. I just replaced my rear main seal on my ‘89 K100 RS Special. I managed to get the new seal in at an even depth, unfortunately, that depth is about 1/8” beyond flush with the housing. (I’m a rookie wrencher.)
Question is: Can I get away with this, or am I setting myself up for disaster?

[Laitch]

Welcome. Are you trying to convey that you have countersunk the seal by 0.125"?

Please post some photos of your moto even though it is a work in progress. Tell us how many miles are on it, how long you've had it and how much you've ridden it.

[Kentallen8]

Yes, that’s exactly what I’m saying. I’m embarrassed to also say I’ve already reattached the clutch housing and transmission before recognizing my mistake. I’d rather not take it all apart again if it is not necessary, since doing so would be more $$.

Regardless, I picked the bike up for a song about two years ago, knowing that the RMS and/or the clutch plate was in its way out. I’ve only ridden it for ~2k miles in that time and the odo is currently sitting at about 65k.

[Kentallen8]

Here are some pics from the disassembly...

[mw074]

  There is plenty of information on how to properly install the seal available. If it's me, I purchase a new seal and re-install it. Any job worth doing is worth doing right. After all, it is " Your Baby. "

[Laitch]

Yes, that’s exactly what I’m saying. I’m embarrassed to also say I’ve already reattached the clutch housing and transmission before recognizing my mistake. I’d rather not take it all apart again if it is not necessary, since doing so would be more $$.

Thanks for the photos, information and clarification.

To my knowledge, there is no cosmic dispensation given to newbies who fail to follow instructions for repair procedures, but that could be changing because we appear to be entering the End Times with climate change and conversion of classic motos into low-slung posermotos as some of the symptoms. Be that as it may, I would follow the same path as mw074 if it were my moto and would install a new seal in the correct orientation; however, you are now in a position to add to the body of Brick knowledge by riding the moto with the seal incorrectly installed and reporting to the rest of us the outcome over the course of your mileage.

It might be that all these procedures with their cumbersome clearance specifications, assembly sequences and requirements for focus are only suggestions—like the Ten Commandments or King Arthur Flour's recipe for buttermilk biscuits—and things will turn out more or less ok depending on your tolerance for chaos and disappointment in the quest for personal convenience.

Please keep us posted.

[The Mighty Gryphon]

I guess I'll throw in a somewhat divergent opinion to further cloud the issue.  I suspect the reason for the original requirement to have the seal proud of the surface is to insure that the lips of the seal are working on an unworn section of the output shaft, the assumption being that if the seal leaks, the cause is a combination of a worn seal and/or shaft.  In the Teutonic mind, it doesn't make sense to replace a worn seal and have it working on a worn spot on the shaft.

As long as your new seal is working on a properly sized and finished spot on the shaft, and isn't bottomed against something behind it that could damage it, there is a very good chance that it will work just as well as a seal that stands proud the proper distance. 

But there's the rub.  Can we be sure that the shaft is finished and sized properly at the spot where your seal touches it?  All we know for sure is that it isn't working in the same spot as the original.

On the other hand, the repair spec calls for the seal to contact the shaft at a spot that was exposed to the external environment and hence may have been damaged at some point in the past.  By installing it where you did, you have put it on a protected part of the shaft.

 :dunno2:

[stokester]

I guess I'll throw in a somewhat divergent opinion to further cloud the issue.  I suspect the reason for the original requirement to have the seal proud of the surface is to insure that the lips of the seal are working on an unworn section of the output shaft, the assumption being that if the seal leaks, the cause is a combination of a worn seal and/or shaft.  In the Teutonic mind, it doesn't make sense to replace a worn seal and have it working on a worn spot on the shaft.

As long as your new seal is working on a properly sized and finished spot on the shaft, and isn't bottomed against something behind it that could damage it, there is a very good chance that it will work just as well as a seal that stands proud the proper distance. 

But there's the rub.  Can we be sure that the shaft is finished and sized properly at the spot where your seal touches it?  All we know for sure is that it isn't working in the same spot as the original.

On the other hand, the repair spec calls for the seal to contact the shaft at a spot that was exposed to the external environment and hence may have been damaged at some point in the past.  By installing it where you did, you have put it on a protected part of the shaft.

 :dunno2:

Having just done this procedure on my '93, I agree that the .5mm proud spec is to ensure the seal rides on a different part of the shaft.  They probably had to deal with a number of come-backs after replacing the seal and the engineers found some microscopic wear on the shaft where it contacted the seal.  Did you replace the O-ring as well?

I tend to agree that I'd ride it and monitor it for leaks.

[natalena]

I can't subscribe to 1/8" off spec being a dramatic detriment to shaft wear.
If it doesn't leak, that's good. If it does, the proper seating is known now.
You are now PIC, here's the yoke, and everyone's counting on you ... "Fear is the mind killer."

[Laitch]

"Fear is the mind killer."

"Don't sleep near a coconut palm during a gale."

[Kentallen8]

I feel like I’ve just gone through an initiation. (Not that it wasn’t warranted, mind you...) Anyway, does this mean I can join the gang now?

Foolish as it may be, I’m inclined to Guinea pig my error in order to add to the knowledge base of this community.

Thanks for the wisdom, and please standby for an ‘I told you so.’

[Martin]

Run it and see if it leaks. If it leaks it is a good idea to linish the seal running surface with very fine wet and dry to remove any flaws in the running surface. A mate of had to replace his rear main seal 3-4 times recently. The non OEM seals had the seal lip further in and with the seal sitting proud as recommended the lip was right on the edge of the running surface and they leaked. Fitting a OEM seal with the lip further back flush with the housing and linishing the running surface fixed the problem.

Regards Martin.

[Laitch]

. . . please standby for an ‘I told you so.’

I'll be moving on now. Don't forget to write.  :wave:

[billday]

Ride it! Later if it's broke,  fix it!

Under my plan,  if you have to take it all apart again,  you can use the time to think about what a good time you had riding.

[Kentallen8]

Ooooh boy do I have an update! As promised - You told me so.

25 miles. That's all the rear main seal lasted. Probably less, actually, but it was at the 25 mile mark that I noticed the bike was hemorrhaging oil out of the weep hole at the back of the engine housing. I managed to have a great and much needed ride, but quickly got it home and set about disassembling everything to figure out what went wrong. Well last night I finally got the short-lived RMS out to see what is what. Turns out the inner lip of the seal ended up getting pressed against the housing for the bearings that surround the output shaft. Apparently that is a bad, bad thing because that inner lip ended up something between torn off and melted off. Check out these photos:

See that gray/black film covering the ring between the output shaft and the bearings? That's the inner lip of the RMS... Fortunately it pulled off as one complete piece, but there were parts of it that were dangerously close to getting sucked deeper into the engine.


Here's a look at what's left of the RMS. Note that the warping on the left hand side is from my seal puller, but that inner lip is pretty much chewed apart from the friction off the engine.

For all you rookie wrenchers like me out there, this is what the engine-facing side of an RMS is supposed to look like:


In a way, the RMS failing so quickly is a stroke of good luck for me, because within this same time I discovered that I also had a very loose grub screw in my transmission, so I had to pull the back half of the bike off again anyway to fix that issue, so the timing let me kill two birds with one stone.

In short - Laitch called it.

PitA as this was, at least I have added new knowledge to the pool.

Learn from my mistakes!

[The Mighty Gryphon]

Your sacrifice is deeply appreciated. 

Re: the grub screw.  While fumbling with getting it screwed back in after degreasing and putting Blue LocTite on the threads you can join the others before you who have spent those moments contemplating why the engineers at BMW decided not to use a thread sealer there when they used it in many other places where it only contributes to making a simple job a PITA.  (Now how's that for a marathon run -on sentence?)

[Laitch]

Under my plan,  if you have to take it all apart again,  you can use the time to think about what a good time you had riding.

25 miles. That's all the rear main seal lasted.

We're building happy memories here regardless of how short they might be.  :yippee: One thing to consider is that perhaps the seal was incorrectly installed incorrectly. :giggles  Be sure to replace the shaft o-ring. That's a source of leakage, too.

To follow up TMG's beautifully crafted thought, it could help others if you start a separate thread about your grub screw repair, or add to an existing thread if you have additional observations about the procedure.

Thanks for the update and the good photos, and thank you for your service.

[The Mighty Gryphon]

To follow up TMG's beautifully crafted thought,

You're making me blush...

[Kentallen8]

...Be sure to replace the shaft o-ring. That's a source of leakage, too.

To follow up TMG's beautifully crafted thought, it could help others if you start a separate thread about your grub screw repair, or add to an existing thread if you have additional observations about the procedure.

Yup, replaced the o-ring. (Both times.)

I thought about making a separate post for the grub screw, but 1) I really didn't have anything new to add to the discussion, and 2) I was not in a desirable/helpful emotional state during that procedure.

[Laitch]

I thought about making a separate post for the grub screw, but . . . I was not in a desirable/helpful emotional state during that procedure.

Don't sell yourself short. It's helpful for us to be entertained by the distress and confusion of others. :giggles

[Martin]

A mate in OZ went through about 4 rear main seals. The non OEM seals had the sealing lip further in causing them to press up against the plastic bearing spacer and probably only just run on the clutch basket running surface. The fix came in two parts, linish the running surface and fit an OEM seal ,the lip runs further back and runs correctly on the clutch baskets running surface. The seal was also fitted flush.
Regards Martin.

[Kentallen8]

A mate in OZ went through about 4 rear main seals. The non OEM seals had the sealing lip further in causing them to press up against the plastic bearing spacer and probably only just run on the clutch basket running surface. The fix came in two parts, linish the running surface and fit an OEM seal ,the lip runs further back and runs correctly on the clutch baskets running surface. The seal was also fitted flush.
Regards Martin.

That sounds equal parts terrifying and soul crushing, and I hope it is not part of my future, thank you very much.