1973 R75/5 Back-to-road Project

anotherbmw said:

I meant the input seal. You are making a good point, hadn't thought about it...What are the chances that these seals go bad? I thought I'd replace because I am in there anyways but I didn't think about the spline situation. Unfortunately I really don't know which of my seals (main, oil pump, or input shaft) were leaking because it was pretty messy in there.

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Olaf,

With the cracked crankshaft flywheel bolt hole, old age of the oil pump seal and original design of the crankshaft rear seal which cuts a groove into the crankshaft nose and leaks, I suspect these created the "oil well blow out" appearance inside the flywheel bell housing. It sounds like you are going to replace all of those and that makes sense.

Changing only the transmission input seal could be necessary, but I'd hold off. You can always tackle that as a separate project. The benefit is, if you pull your transmission back to lube the input splines in about a year or so, you can easily see if that seal is leaking. IF so, I'd recommend replacing all the transmission seals.

Hope that helps.

brook.reams said:

Olaf,

With the cracked crankshaft flywheel bolt hole, old age of the oil pump seal and original design of the crankshaft rear seal which cuts a groove into the crankshaft nose and leaks, I suspect these created the "oil well blow out" appearance inside the flywheel bell housing. It sounds like you are going to replace all of those and that makes sense.

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The flywheel was bone dry though, so I doubt that any oil leaked through the flywheel bolt holes. In any case, Amazon is going to drop off the Permatex tomorrow, so I am not taking any chances with that one! I think I'll follow your suggestion and leave the transmission alone for now. If I really have to get back in there it's not that bad to take it out again. Thanks again for the input!

Back to the transmission input seal, it seems that the inner diameter of the seal is larger than the diameter of the spline, so what you brought up earlier doesn’t seem to be an issue with the 4-speed tranny!




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anotherbmw said:

Back to the transmission input seal, it seems that the inner diameter of the seal is larger than the diameter of the spline, so what you brought up earlier doesn’t seem to be an issue with the 4-speed tranny!

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Olaf,

No, this is the same clearance as on the /6 input shaft. Without protecting the seal when you drive it in, you will likely damage the lip of the seal and/or pop the spring that fits in the groove on the back of the seal out of place as it passes over the shoulder on the input shaft that is behind the splines. Either will prevent the seal from sealing.

Other Pictures

The rest of the pictures for installing the input seal:

Oh I see what you mean. I didn't think that step at the bottom of the spline would be an issue, it is slightly tapered, I'll take another look tomorrow, thanks!

Running engine without clutch and transmission installed?

As the title says, can I fire up the engine with flywheel installed and clutch and transmission still out? I don't see why not.

I just want to warm up the engine and see if my main seal repair and and oil pump o-ring are holding up. I have some pods I can stick on the carbs to keep the June bugs out, but would there be any other concern? Thanks!

I'm thinking that if you normally had the transmission and driveshaft installed and started the bike in neutral, what's substantially different if the transmission/clutch were not there? You're just permanently in neutral. So, I can't think of any reason to not do what you want. Unless you have a massive problem, you'll not likely see anything happen in such a short time.

Successfully finished the main seal replacement. After 150 mls, no leak at all! It was a bit of work but all went reasonably well. I am glad I had some special tools (little extension wrench to torque the driveshaft bolts, flywheel puller, clutch centering tool). They definitely made my life easier. Thanks again everyone for y’alls input. Below a few pics.












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anotherbmw said:

Successfully finished the main seal replacement. After 150 mls, no leak at all! It was a bit of work but all went reasonably well. I am glad I had some special tools (little extension wrench to torque the driveshaft bolts, flywheel puller, clutch centering tool). They definitely made my life easier. Thanks again everyone for y’alls input. Below a few pics.

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Hi Olaf,

Congratulations on finishing the project. It feels good when the results improve the ride.

BTW, one comment on the input shaft spline lube. There is much more lube shown on the splines int the picture above than you want to put there. If you use the Molypaste 60 (or equivalent), the moly adheres to the steel and "plates" it providing the lubrication at high contact pressures that you need. Best practice is to use a tooth brush (or solder flux brush) to apply a little to all the splines, then use a rag to wipe off the excess. This prevents lube from being flung off the shaft and potentially onto the clutch plate. Extra lube does nothing for protecting the spline faces.

Hope this helps.

Best.
Brook Reams.

lube

Even better still, put the lube on the clutch splines. That way when you slide the transmission in place, the excess lube is pushed away from the input seal. This idea also works with the rear wheel splines. Lube so that things don't bunch up at the critical location of the seal.

brook.reams said:

BTW, one comment on the input shaft spline lube. There is much more lube shown on the splines int the picture above than you want to put there.

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Brook, thanks for the feedback. So the photo is misleading, I took it after I spread a bunch of Staburags on there, I then used a toothbrush and rubbed it into the groves and removed the excess. So it did not look this way when I put it together (I guess I shouldn't have posted it like that). I pretty much followed the steps in Chris Harris' video. Thanks for pointing it out. And the bike runs great, 200 mls and no issues!

anotherbmw said:

Brook, thanks for the feedback. So the photo is misleading, I took it after I spread a bunch of Staburags on there, I then used a toothbrush and rubbed it into the groves and removed the excess. So it did not look this way when I put it together (I guess I shouldn't have posted it like that). I pretty much followed the steps in Chris Harris' video. Thanks for pointing it out. And the bike runs great, 200 mls and no issues!

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Olaf, Sounds like you are really getting into your project, but Staburags is so 2013! There are much better choices out there today. Snowbum will have at least 19 pages of more current choices for spline lube. By the time you decipher his advice there will probably be an improved product.

Friedle

Friedle said:

Olaf, Sounds like you are really getting into your project, but Staburags is so 2013! There are much better choices out there today. Snowbum will have at least 19 pages of more current choices for spline lube. By the time you decipher his advice there will probably be an improved product.

Friedle

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Hey my bike is 1973 so the "antiquated" 2013 Staburags doesn't seem old in comparison Honestly I don't think it makes much of a difference, from what I hear/read there are many products that do the job, and there are even many more opinions out there what to use. I tend to just pick what is recommended by one or more "gurus" and that's it.

Gone for a looooong time....

I just realized I haven't been on this forum for a very long time - for good reason! Already put around 2,500 miles on my Airhead (actually I need a new rear tire!) and recently required a 1995 R1100 GS, so I have everything I need in my garage now! Will post some pics of all my beauties combined soon. Now I need to venture over to the Oilhead forum to get some things sorted

I am restoring a 1971 R75/5 right now. I will read this thread when I have more time but what I have read so far is pretty good. I had a serious leak on my engine or transmission also. I will be installing a new gasket and seal kit on the motor and the transmission.

Running great!

Wow, just realized I haven't posted here in a while! Reason is the bike runs so well (rear tire is already gone) and I also picked up an 1100 GS Oilhead that I am working on.

I got a good deal on Wixom bags with racks for my airhead, they look ok, but I would like to restore them some more. Does anyone know of any sites (Duane Ausherman has some info) that could be helpful? Thanks!

brook.reams said:

Olaf,

The crankshaft has drilled oil passages inside. When the flywheel mounting holes are drilled and tapped in the end of the crankshaft, sometimes they are a bit too deep and the bottom of the hole cracks connecting the hole to one of the crankshaft oil passages. Hence the leak when you pull a flywheel bolt. This happens enough that mine was not unique according to Tom Cutter.

As I show in the write-up this photo was copied from, I measured the depth of the RTV to avoid overfilling the flywheel bolt hole.

11 BMW 1973 R75/5 Remove & Install Flywheel, Replace Rear Main Seal, Oil Pump Cover & Cover O-Ring

The flywheel bolt torque changed with the change in bolt diameter from 10 mm to 11 mm which I believe was at the start of the /6 series in 1974. You can read about the proper torque and preparation of the flywheel bolts here.

--> http://bmwmotorcycletech.info/torquevalues.htm

Hope this helps.

Best.
Brook Reams.

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I am restoring a 1971 R75/5. I had oil come out of my flywheel bolts also. I have spent many hours on your web page so I had already read your theory on where the oil comes from. I wasn't not fully sold on the theory so I conducted a test. I stood my crank up vertically with the flywheel holes facing up. I filled all of the holes with degreaser and waited for the fluid to leak out into this oil passageway that you speak of. Nothing happened. I left it over night. still nothing.

I have read several times that in the later years BMW had added a oring to the flywheel where it goes onto the crankshaft. Everytime I came across this info I wondered why they would do this then it finally dawned on me. If there is only a rear main seal with no oring on the back of the crankshaft/flywheel connection then couldn't oil, over time, leak from the engine, between the flywheel and the end of the crankshaft, leach into the bolt holes, and weep out of the flywheel/crank connection??
Could this in fact be where the mystery oil is coming from when we remove the bolts from the flywheel on these old engines?

Supercool_Bill said:

I am restoring a 1971 R75/5. I had oil come out of my flywheel bolts also. I have spent many hours on your web page so I had already read your theory on where the oil comes from. I wasn't not fully sold on the theory so I conducted a test. I stood my crank up vertically with the flywheel holes facing up. I filled all of the holes with degreaser and waited for the fluid to leak out into this oil passageway that you speak of. Nothing happened. I left it over night. still nothing.

I have read several times that in the later years BMW had added a oring to the flywheel where it goes onto the crankshaft. Everytime I came across this info I wondered why they would do this then it finally dawned on me. If there is only a rear main seal with no oring on the back of the crankshaft/flywheel connection then couldn't oil, over time, leak from the engine, between the flywheel and the end of the crankshaft, leach into the bolt holes, and weep out of the flywheel/crank connection??
Could this in fact be where the mystery oil is coming from when we remove the bolts from the flywheel on these old engines?

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Hi Bill,

The "theory" is via Tom Cutter whose experience with airhead engines is pretty extensive. I only had one bolt show oil coming out of the crankshaft hole and that came from a crack that connected that hole with an oil galley in the crank.

You say, "I had oil coming out of my flywheel bolts also." I take it the plural "bolts" means you saw oil at multiple bolt holes. Was the oil coming out of multiple holes when you removed the bolts?. Or, I could interpret this to mean multiple, or all, the bolts had oil around them before you removed them, so I'm not exactly sure which interpretation is correct.

If there was oil covering multiple bolts, I wonder if that might have come from a failed oil pump O-ring, or a rear crankshaft seal that cut a groove in the crankshaft and leaked? In either of those instances, there is usually a lot of grunge inside the bell housing from clutch dust mixing with the oil that gets slung around.

I don't know the exact reason BWM added the O-ring to the flywheel starting in the 1976 model year, but I suspect it was to stop oil leaks occurring from the original crankshaft seal design. Later, they changed that seal to PTFE teflon which eliminated the seal cutting a groove in the crankshaft.

Best of success on your rebuild and have a merry Christmas.

Best.
Brook Reams