Oil Leak from Kickstarter Shaft (R51/3)

[Micha]

I came back from riding about 60 miles and when I parked the bike I saw after ca. 15 minutes that there is a leak from there.

1. Do I have to take the engine/gearbox out of the motorcycle to replace the oil seal there? Or can the oil seal be replaced by disassembling the kickstarter lever, the battery, the horn and all the other items that are in the way there?

2. Why did a leak even start there? Could it be that I have a problem with the engine breather? Then replacing that seal ring won't help at all here.

3. The entire engine was assembled with new gaskets and oil returners about 500 miles ago. Is this the lifespan of oil returners in these engines?

Any help and ideas would be greatly appreciated.

[schrader7032]

I don't think the leak has anything to do with engine breathing. The transmission has its own cavity and it's own fluids. Could be that the engine speedometer bolt isn't breathing and building up too much pressure inside. This seal is well above the top of the fluid sitting in the sump, so it's leaking from the oil splash during running. My guess is that the transmission would have to come out, just to do the job correctly and more easily.

[Micha]

Of course, there is no connection between the two oil fields. I was not focused.
Thanks, I'll check the speedo cable connector.

[Micha]

I went to the motorcycle and checked carefully with a flashlight: all the oil came out of the gearbox, that is empty now. Everything happened suddenly and at once. The last time I drove about 60 miles it was a pretty cold day and all was fine with no oil loss. This time it was already warmer (about 77 F) and I'm starting to think that maybe the oil I put in the gearbox is too thin? I use Castrol Classic XXL 40 engine oil according to the manufacturer's instructions, but maybe I should change to 90 gear oil? Could it be that this engine oil heats up and its expansion breaks the seal of that kickstarter shaft?

I think that if there is wear on the kickstarter shaft itself, then the oil would start sweating and slowly come out. My case really looks like the tranny can't breathe but I checked that drilled bolt that holds the speedometer drive assembly, and it is new, wide open and easily passes the air I blow through it.

Any ideas?

[schrader7032]

Viscosity systems for engine oil and gear oil are different. So 40/50 weight engine oil is about the same viscosity as 80/90 weight gear oil. Gear oil should only be used if you have installed the proper seals as identified by BMW in their service bulletins.

That's pretty drastic to have all the oil come out of the gear box. On my R69S, the kick start seal is above the fill level of the transmission. How can that much oil get so high?

[Micha]

All I remember is that I filled oil up to the level of the cap, until I saw it in the opening.
AFAK - these are also the instructions that appear in the workshop manual.

[cbclemmens]

Kurt:

I am going to have to disagree with you on viscosity. Viscosity is a scientific measurement of a fluid's resistance to flow.
The viscosity of water is 1.0. Fluids thinner than water, like alcohols and air, have viscosities in decimal points. Thicker fluids have larger numbers. Double numbers, like 20W50 or 75W90, indicate that the fluid contains a stabilizer that prevents the fluid from "thinning out" under the heat of operation. BUT there are NOT different numbers for different fluids. If a gearbox spec calls for a 40 weight oil lubricant then use a 40 weight oil. Running a thicker oil risks damaging the unit. The clearances may be too tight for the thicker oil to penetrate and properly lubricate the moving parts.

Craig

[schrader7032]

Craig -

I'm not sure but we may be talking past each other. I never mentioned a multi-vis oil. I was comparing something like a 40w engine oil viscosity to that of a 90w gear oil. They must have relatively the same viscosity. I suggest that because BMW went from specing 40w engine oil in transmissions to later calling for 90w gear oil. What changed?? Only the style of seals were changed, seals that worked well with gear oils. So it seems to me that a 40w engine oil has to be in the ball park of a typical gear in terms of viscosity.

General concept was mentioned at the bottom of this post:

viewtopic.php?p=85592#p85592

Nice chart on this page:

https://blog.amsoil.com/gear-oil-vs-engine-oil/

[Slash2]

I seem to recall reading that hypoid gear oil is more effective at reducing wear on helical gears and perhaps that’s what caused the change in recommendation.

[metoo]

The only way for the transmission to totally drained out is leak from the lower oil remove bolt or a crack in the housing