1150r Rear Main Seal issues/leak

Hi All,

1st post on here, I'm hoping you can assist me!

I have an 04 Rockster with a leaking rear main seal. I'll keep this as brief as possible as I'm on my 4th seal and its still leaking!

Summary:
Internal seal replaced, looks dry when outer seal removed
Outer seal replaced, 3 times. Have ensured the seal is flush with casing and installed with lip inverted to clear the crank breather.
Each time I replace, the seal leaks, it looks to be from outer edge and not the internal part sealing the crank.
Have checked the oil breather and this is clear.

I have been told it could be the worn crank bearings forcing an elliptical rotation which could put some pressure on the seals and cause the leak. It looks like a small leak has now formed on the front main seal so this does support the bearings as the possible issue.

Questions:
If worn bearings, I would assume the inner main seal would also leak?
Could worn bearings lead to a leaking rear main seal
anything else I need to check?

I do have pictures, video etc I can upload if anyone is interested.

its super frustrating, any guidance is much appreciated!

Are you using fully synthetic oil by any chance??

If you were getting that much movement you would hear or feel it

That's a lot of mass to be able to jump about

I have heard plenty of people talking about leaks from fully synth oils over the years

yes a 20/50 mineral oil ,is what is needed ,i have also had leaks with synthetic oil on an old r1100rs

DrFarkoff said:

Are you using fully synthetic oil by any chance??

If you were getting that much movement you would hear or feel it

That's a lot of mass to be able to jump about

I have heard plenty of people talking about leaks from fully synth oils over the years

Click to expand...

I'm using Castrol Activ, 15-50, it's a recommended oil that's a semi-synthetic.

The bike has not been ridden, its an engine I picked up with a new top-end. The guy did say there was a leak, I should have started it before changing the seal the 1st time to have a better picture if the leak was small or big. When I start the bike, oil runs down the engine, and after 5 minutes the flywheel is pretty wet. next step is to have a camera behind the flywheel to better understand the leak.

addiing to the thread. I have attached some pictures taken just now. it shows the inner seal as dry. The leak seems to be from the outer seal only, as when I remove it after running the bike, the internal seal is dry. Maybe the leak is not coming from the outer seal, can't see as the flywheel is in the way! I'm open to any ideas here, super frustrating!

Link to pics.
https://drive.google.com/drive/folders/1ubhwmbYuEtlWcSUAAN2SSBBDMhZzevSG?usp=sharing

Maybe the crankcase halves were poorly sealed from new?

possible, the bike is used, I can only assume it was working ok. I have installed another seal and will try to get a small camera in there to record