Rear Main Seal

[bbelk]

It is time for the semiannual greasing of the splines. It still amazes me that BMW considers this a maintenance item. It is obviously leaking a little bit of oil, but how do I tell where it is coming from. Its either the main seal, the seal around the oil pump or the front of the transmission. I think this gunk is engine oil and not transmission oil, but I am not sure.

How do I get that main seal out? How do I get the new one in? I have no special tools. I have read something about blocking the crank shaft. Whats that about.

Is it wise to replace the oil pump gasket as a preventative? Any suggestions will be appreciated.

The bike is an 1975 R90/6. The big drip in the picture came from the bolt holes.

[lrz]

Not to be alarmist, but your crank should be blocked at this point if that photo is current...that is accomplished by pinning the rotor bolt in place to the back of the front engine cover through applied pressure such as an appropriate length nylon bolt.
A run of the mill seal puller from any auto parts store will work or screws used judiciously as a levering point. The install depth is key and there is a "special tool" for that. Do NOT gouge the seal surface.

[Kurt in S.A.]

When I had a tranny input shaft seal removed, the dealer used some kind of claw to dig into the seal and then levered it out...they did it for free since I brought the tranny to them and they probably took pity on my attempts at using screws into the seal and my makeshift slide hammer. A guy on the MOA forum has just shown some pictures on how he takes them out by getting a grip of the edge and with some twisting action, collapses the seal inward which then allows it to easily be pulled.

Unless you've done some cleaning of the shelf below the RMS and oil pump cover, I'd say your leak is on the transmission side. Your shelf looks bone dry.

Kurt in S.A.

[bbelk]

Not to be alarmist, but your crank should be blocked at this point if that photo is current...

Ok - I have the crank blocked. I had to be careful of my Omega so there is a bolt drilled into the block in the picture that sits down inside the allan bolt on the rotor.

[bbelk]

Unless you've done some cleaning of the shelf below the RMS and oil pump cover, I'd say your leak is on the transmission side. Your shelf looks bone dry.

Kurt in S.A.

I may have hit that tray at the car wash before digging into things - but I don't understand why crank case oil would end up there and transmission oil would not. It seems like they are both dumping into the same cavity.

[Kurt in S.A.]

Well, you're right there...they both drain to the same point. If there was enough oil sitting on the shelf, then it may have been possible to smell the difference in a drop on your fingertip. A sulphur smell would be gear oil. But the other way is that once the tranny is off, the stain of oil is pretty obvious running down the front of the bell housing, as would be the case running out from behind the flywheel.

Kurt in S.A.

[Airbear]

While you are in there you may as well replace all three seals.

Here's the 'special tool' you need to replace the RMS -



The bolts and nuts shown are the ones you need to remove and replace the clutch. Use three of your crank bolts to pull the new RMS into position. Here's the geometry for that 'special tool'. Note the position of the old RMS before pulling it out.



BMW specifies that the crank bolts and clutch bolts must be replaced with new because they are 'stretch' type. Some people don't, but I did. It is worthwhile getting new screws for the oil pump cover as well, since you might stuff up the heads getting them out - use an impact driver there to remove them.

re blocking the crank, though the bit of wood and electrical ties will work it may be difficult to avoid turning the crank when you are reassembling. I suggest you cut a stub of Allen key for the alternator bolt and screw the front cover on. I think 3/4" to 1" in length is about right.

Good luck with it. There's a nice feeling of accomplishment when it's all done.

[Garnet]

After 76 you'll need to put 11 mm holes in Charl'es beuatifull drawing.

[Duane Ausherman]

The seal installer makes the job easier, but if I only had one to do, I would just tap it in. I have done it plenty of times.

The transmission oil migrates along the input shaft, either on the inside or outside. Both dump on the clutch friction plate. Oil leaking past the seal at the shaft surface can/will run down the front. Rare, but possible, is the case where the oil can leak past the outside of the seal and then you will see it dribble down the front. If it is clean and you have no trail down the front of the transmission, then it is engine oil. They smell completely different. Test both and then smell the oil that leaked out.

You didn't mention that the clutch plate was covered in oil, so it isn't leaking along the pushrod shaft.

You can get all of this online too.

[bbelk]

While you are in there you may as well replace all three seals.

Here's the 'special tool' you need to replace the RMS -
........... There's a nice feeling of accomplishment when it's all done.

Oh but for a few minutes. This is a brilliant solution that is within my skill set. If I had recived it a little earlier, I would have avoided this piece of brillance:



I had the bike up on the lift, tied it to the ceiling, dropped the lift, backed in the trailer, raised the lift, strapped the bike to the trailer, dropped it down and towed it to a shop that had the "special tool".

I would add my own little modification to that special tool would would be to oversize it slightly and then route the correct diameter at the proper depth so that the seal would be set right. But of course without your picture, I didnt' think of any of this.

I hope you appreciate my able assistant in this matter. She isn't much help in the "what to do next" catigory, but she really dresses up a picture.

You mention three seals. Is that the RMS, the transmission input shaft and (guessing here) the oil pump gasket?