Rear main leak...or ???

woodly1069 · 01-06-2013, 05:01 PM

Ok fellas I have pulled my old R75/5 all apart for more reasons than just one but this is on the list to repair. I have had a small leak and assumed it was the rear main. After pulling things apart I really dont know if the main was leaking at alll. I will replace it but it looks to me as if this lower plate may be the actual culprit, what do you think?

I know it's hard to see but the main seal looks in tact. Could it be the lower plate seal also?

JonnyCash · 01-06-2013, 05:34 PM

From your pictures, I would say you're right, it's the oil pump cover. There's an o-ring under that cover. If it were the rear main, I'd expect to see oil thrown all around, not just down.

disston · 01-06-2013, 05:54 PM

It looks like that is the original rear main seal. Make sure you change it. It has served well but it's time to go has come.

The oil pump cover O-rings do go bad and leak.

Brun · 01-06-2013, 06:10 PM

And do replace the transmission input shaft seal as well.

woodly1069 · 01-06-2013, 06:28 PM

Will do, just as I expected! THANKS GUYS!

jackd · 01-06-2013, 07:15 PM

Maybe someone has changed the rear main seal in the intervening time since the bike was built - it seems to be dry as a bone and who knows what age it is? Personally I wouldn't go farther than changing the oil pump cover seal - that seems to be a logical thing to do. But then I don't like finding more work than I have to. Your call.

Kai Ju · 01-06-2013, 07:16 PM

Did you block the crank ? Please say yes.....

woodly1069 · 01-06-2013, 07:36 PM

I think I will change the rear main as well as the oil pump plate seal; hopefully that will do the trick. As far as blocking the crank I am unfortunately in the dark, what do you mean?...please advise.

ozmoses · 01-06-2013, 07:41 PM

STOP!

If your crank rotates it may shift forward coming off the thrust bearing.

http://bmwmotorcycletech.info/flywhe...valwarning.htm

ignatz72 · 01-06-2013, 07:41 PM

Oh boy...

woodly1069 · 01-06-2013, 07:45 PM

OK call me stupid, I'm sure the thing rotated at least 90 degrees but I marked it and put it back where it was when I started. How does it come off the thrust bearing? I don't understand...isn't the thrust incorporated into the mains?

ozmoses · 01-06-2013, 07:56 PM

You're not stupid. Read the link I provided, all the info is there.

woodly1069 · 01-06-2013, 07:58 PM

OK thanks

jackd · 01-06-2013, 08:16 PM

All is not lost. Pull the front cover off the engine (by the alternator) and see where your alternator brushes presently are running on the rotor slip ring. If the crank has slipped ahead the carbon brushes will be contacting to the rear of where they usually locate. If they are still running in the same spot as usual then the crank hasn't moved and the thrust bearings have not come off their perches. If that's the case, then now is the time to block the crank at the front of said alternator.

If your level of experience is limited with these machines then maybe you should take a pass on doing the rear seal and stick to the oil pump cover.

ME 109 · 01-06-2013, 08:21 PM

Some good detective work there jackd.
Those dowels/pins that retain the thrust washer are about three mm long from memory.

01-06-2013, 05:01 PM	#1
woodly1069 ^OP Beastly Adventurer Joined: Jun 2008 Location: Louisville, KY...really too far from the hills! Oddometer: 1,099	Rear main leak...or ??? Ok fellas I have pulled my old R75/5 all apart for more reasons than just one but this is on the list to repair. I have had a small leak and assumed it was the rear main. After pulling things apart I really dont know if the main was leaking at alll. I will replace it but it looks to me as if this lower plate may be the actual culprit, what do you think? I know it's hard to see but the main seal looks in tact. Could it be the lower plate seal also? __________________ If you can't fix it with a hammer, you've got an electrical problem!

01-06-2013, 05:34 PM	#2
JonnyCash turd polisher Joined: Jan 2011 Location: Midcoast, Maine Oddometer: 774	From your pictures, I would say you're right, it's the oil pump cover. There's an o-ring under that cover. If it were the rear main, I'd expect to see oil thrown all around, not just down. __________________ I wouldn't bring her home to Mama, but Mama ain't home tonight.

01-06-2013, 05:54 PM	#3
disston ShadeTreeExpert Joined: Mar 2011 Location: Silver Spring, Md Oddometer: 5,025	It looks like that is the original rear main seal. Make sure you change it. It has served well but it's time to go has come. The oil pump cover O-rings do go bad and leak. __________________ Never memorize something you can look up. ---Albert Einstein

01-06-2013, 06:10 PM	#4
Brun Adventurer Joined: Jun 2012 Location: BorderBurg, South East Oz. Oddometer: 52	And do replace the transmission input shaft seal as well. __________________ Cheers Charlie, and the lovely Brunhilde (74 R90/6)

01-06-2013, 06:28 PM	#5
woodly1069 ^OP Beastly Adventurer Joined: Jun 2008 Location: Louisville, KY...really too far from the hills! Oddometer: 1,099	Will do, just as I expected! THANKS GUYS! __________________ If you can't fix it with a hammer, you've got an electrical problem!

01-06-2013, 07:15 PM	#6
jackd Beastly Adventurer Joined: Dec 2006 Location: North Cowichan Oddometer: 2,373	Maybe someone has changed the rear main seal in the intervening time since the bike was built - it seems to be dry as a bone and who knows what age it is? Personally I wouldn't go farther than changing the oil pump cover seal - that seems to be a logical thing to do. But then I don't like finding more work than I have to. Your call.

01-06-2013, 07:16 PM	#7
Kai Ju Beastly Adventurer Joined: Jul 2009 Location: So Cal Oddometer: 1,026	Did you block the crank ? Please say yes.....

01-06-2013, 07:36 PM	#8
woodly1069 ^OP Beastly Adventurer Joined: Jun 2008 Location: Louisville, KY...really too far from the hills! Oddometer: 1,099	I think I will change the rear main as well as the oil pump plate seal; hopefully that will do the trick. As far as blocking the crank I am unfortunately in the dark, what do you mean?...please advise. __________________ If you can't fix it with a hammer, you've got an electrical problem!

01-06-2013, 07:41 PM	#9
ozmoses Ride On Joined: Jul 2009 Location: USA Oddometer: 1,068	STOP! If your crank rotates it may shift forward coming off the thrust bearing. http://bmwmotorcycletech.info/flywhe...valwarning.htm __________________ Opinions are like internet connections- everybody has one. ozmoses screwed with this post 01-06-2013 at 07:46 PM

01-06-2013, 07:41 PM	#10
ignatz72 call me iggy Joined: Aug 2010 Location: Mid-South, M-town Oddometer: 600	Oh boy... __________________ Current: 93 R100GS, 04 XR650L Prior: 73 CB350, 77 R100/7, 83 R100RT I love every motorcycle I've owned and even some that I haven't.

01-06-2013, 07:45 PM	#11
woodly1069 ^OP Beastly Adventurer Joined: Jun 2008 Location: Louisville, KY...really too far from the hills! Oddometer: 1,099	OK call me stupid, I'm sure the thing rotated at least 90 degrees but I marked it and put it back where it was when I started. How does it come off the thrust bearing? I don't understand...isn't the thrust incorporated into the mains? __________________ If you can't fix it with a hammer, you've got an electrical problem!

01-06-2013, 07:56 PM	#12
ozmoses Ride On Joined: Jul 2009 Location: USA Oddometer: 1,068	You're not stupid. Read the link I provided, all the info is there. __________________ Opinions are like internet connections- everybody has one.

01-06-2013, 07:58 PM	#13
woodly1069 ^OP Beastly Adventurer Joined: Jun 2008 Location: Louisville, KY...really too far from the hills! Oddometer: 1,099	OK thanks __________________ If you can't fix it with a hammer, you've got an electrical problem!

01-06-2013, 08:16 PM	#14
jackd Beastly Adventurer Joined: Dec 2006 Location: North Cowichan Oddometer: 2,373	All is not lost. Pull the front cover off the engine (by the alternator) and see where your alternator brushes presently are running on the rotor slip ring. If the crank has slipped ahead the carbon brushes will be contacting to the rear of where they usually locate. If they are still running in the same spot as usual then the crank hasn't moved and the thrust bearings have not come off their perches. If that's the case, then now is the time to block the crank at the front of said alternator. If your level of experience is limited with these machines then maybe you should take a pass on doing the rear seal and stick to the oil pump cover.

01-06-2013, 08:21 PM	#15
ME 109 Studly Adventurer Joined: Jun 2009 Location: Albury Australia Oddometer: 617	Some good detective work there jackd. Those dowels/pins that retain the thrust washer are about three mm long from memory. __________________ Lord of the Bings

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