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Rusty Cage
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Auburn California
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I took my 1975 R75 /6 for its first real ride in 26 years. When I got back I discovered oil leaking from somewhere above the oil pan area of the motor and under the gear box. That is where the gear box mount to the motor at the clutch area. Any ideas before I start taking it apart? Not sure if these pictures can do any service.

  • bwm_leak_1.jpeg
  • r75_1.jpeg
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1966 R69S - second owner, original condition
1975 R75 /6

Darryl.Richman
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Surf City, USA (Santa Cruz, CA)
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The "Tray"

Basically, the area you are looking at is part of the motor case casting that juts out under the transmission. On the /2 and /3 bikes, this is a little catch area; on the Airheads, oil can come out between the casting and the motor mount tube.

This tray will catch oil that leaks from either of two places, and it lets you find the trouble before it oils up your rear tire. The two places (3, actually, on Airheads) are the motor rear main seal, the transmission input seal, and on Airheads, the oil pump cover seal.

All three of these have the potential to oil up your clutch, so when you notice oil there, you would be wise to take the time/money to pull the transmission and see what's happening in there.

If the oil in the tray has a strong sulfur smell - assuming you're using hypoid gear lube in the transmission - it means the input seal is leaking. If not, it's probably motor oil.

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Rusty Cage
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Thanks, it does seem to have

Thanks, it does seem to have a sulfur smell to it. I guess I'll pull it apart and see what I find. Thanks for your help.

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1966 R69S - second owner, original condition
1975 R75 /6

khittner
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If you're going to pull

If you're going to pull the transmission out to check the input shaft seal, I would go ahead and replace the rear main and oil pump seals in the engine case while you've got access to them. On a bike that's gone unridden for as long as yours, it's not whether those seals will leak---it's more a matter of how soon after resuming use that they'll start leaking.

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Konrad

schrader7032
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San Antonio, TX
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Rear main seal requires the

Rear main seal requires the flywheel to be removed. It is very important that you block the crankshaft before removing the flywheel to prevent any movement of the crankshaft and upsetting the locating pins. Otherwise, damage can occur when reattaching and torqueing the flywheel back. Very important!

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Rusty Cage
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Ok, I'll go slowly and might

Ok, I'll go slowly and might be back here for some advise. Good winter project I suppose. Thanks for your help.

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1966 R69S - second owner, original condition
1975 R75 /6

Rusty Cage
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Auburn California
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how do you block the crank shaft?

I have the gear box off and have the seals. I think the leak is coming from the motor side. I bought a new clutch and need to get the longer screws and nuts to remove the pressurized clutch plates. Once I get that off, I plan to change the oil pump gasket. As for the rear main seal, how do I go about blocking the crankshaft as described above?

Also, to change the input shaft seal on the gearbox, I imagine you have to open it and take it apart? Are there any tricks to it once you open in it? Any gears that must line up? Any special precautions?

And do you have some recommended steps to change the main seal? I've never been in here before and don't want to mess anything up.

The book shows the need for some device to line of the clutch plates when re-installing. The device goes in where the transmission shaft would go. Any additional info on that?

Thanks again for the help.

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1966 R69S - second owner, original condition
1975 R75 /6

schrader7032
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San Antonio, TX
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Blocking crankshaft: Lots to

Blocking crankshaft: Lots to read about here - http://bmwmotorcycletech.info/flywheelremovalwarning.htm

Transectomy: Yes, it's somewhat of an art. Heat is needed to remove the rear cover. The parts have to fit just right...best to replace things if you can tell what needs replacing. Reassembly required careful shimming of the shafts otherwise you'll destroy bearings and/or the gear box. Cycleworks sells a rear plate for doing the shim measurements. Not for the faint-of-heart. Couple of links to this:

http://www.ukgser.com/forums/showthread.php/271570-Airhead-Gearboxes
http://jhau.maliwi.de/mot/gearbox.html

Rear main seal: See Snowbum's page above

Clutch alignment: I don't think you need anything. I did my /7 clutch and just kept looking at the rear of the clutch pack and made sure that the clutch disk was as centered as I could get it as I was tightening the pressure plate. If you're changing out the input shaft, that would be a perfect alignment tool.

BTW...why do you think you need to replace the input shaft? You can replace the front input shaft seal from outside the gearbox. You just need an appropriate puller...they're like a claw with a sharp point that grabs the rubber seal. Be careful not to scratch the sealing surfaces.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Rusty Cage
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Auburn California
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thanks

Thanks Schrader, that was a question I had. I only need to change the input seal so I wanted to be sure it could be done without opening the gearbox.

Wow, yes, there is much to read and know before going beyond the clutch to the fly wheel. I'll take this slow and start reading for understanding. Thanks for the help and info.

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1966 R69S - second owner, original condition
1975 R75 /6

schrader7032
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San Antonio, TX
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This is a seal puller that

This is a seal puller that could be used:

https://www.amazon.com/Lisle-56750-Seal-Puller/dp/B0002SRCKG

When I was doing my input seal, I tried another method. I carefully, very carefully drilled holes in two spots of the seal so I could screw in some sheet metal screws. I rigged a slide hammer to try and "jerk" the seal out. It wasn't budging, so I took the transmission up to my locak BMW dealer. In 15 seconds, he had the seal out using something like above. He was nice about it...didn't charge me a thing.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Rusty Cage
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Auburn California
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Nice. I'll take a look at

Nice. I'll take a look at getting it. I think they sent me the wrong seal cause it seems to be a bit bigger. So I'll have to see. I'll have to really review the flywheel removal process. It is very intimidating and I don't want to mess anything up. So I'll need to do plenty of homework on it before doing anything.

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1966 R69S - second owner, original condition
1975 R75 /6

Rusty Cage
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Auburn California
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thanks for the help

Thanks to your help. I was able to replace the clutch, the rear main seal and oil pump o-ring without doing any damage to the motor. All went smooth. As it turned out, the last time someone changed the rear main seal, they had nicked the metal with the tool and left a metal shard that was creating a poor seal. So with some delicate reworking of the area, it is good to go and the new seal is seated. Ready for summer. Thanks again for advice.

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1966 R69S - second owner, original condition
1975 R75 /6

Rusty Cage
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Auburn California
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And as it turned out the

And as it turned out the gearbox was fine and the seal was as well. So nothing was necessary for the gearbox.

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1966 R69S - second owner, original condition
1975 R75 /6

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