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1973 R75/5 Back-to-road Project

Dang, do I have to order the shorter bolts then? If so would you know the part number? Thanks!

Unfortunately, the part number I believe is the same...BMW does that from time to time. But if a dealer has the older bolts in stock, they will sell you those. But you should really ask for the shorter bolts.
 
Bob's BMW has the whole fork rebuild kit: seals, rubber bumper doofers that turn to mush inside the forks, new progressive springs, all the crush washers (small and large), new 13 ring rubber gators, and the bottom rubber dust caps.

I need to call them
but can't seem to find this rebuild kit on their website
anyone know off hand, what item number or how to find this kit?

thanks in advance
brant
 
Unfortunately, the part number I believe is the same...BMW does that from time to time. But if a dealer has the older bolts in stock, they will sell you those. But you should really ask for the shorter bolts.

Ok, i found them on some other websites as well, glad I asked and thanks for the info!
 
Surgery started...

Unfortunately, the part number I believe is the same...BMW does that from time to time. But if a dealer has the older bolts in stock, they will sell you those. But you should really ask for the shorter bolts.

I ordered the shorter flywheel bolts (thanks again for pointing that out) and started disassembling.

I also ordered Staburags to lube the transmission spline, as recommended by Chris Harris and was wondering if I can use that stuff on the final drive spline as well. My thought was "yes", since the movement on the transmission spline is lateral plus torque and the final drive is torque only and Staburags has the Moly in there. Any opinions on this one?
 
Just pulled the transmission and I am wondering, does this look more like a transmission seal leak than the main engine seal? Everything I wipe off here is black and does definitely not look like my fresh engine oil. I haven’t pulled the clutch and flywheel yet, so I will get more insight then.
Assuming it is the transmission input shaft, it appears to me I can replace that from the outside without opening the transmission, right? As always, thanks for any feedback!

82b42c69fe91bf1551c3c6e3439446c4.jpg


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Sent from my iPhone using Tapatalk Pro
 
You should make sure that the oil has more of a gear oil smell, ie, more sulphur before you start yanking the flywheel, etc. Yes, the input seal to the transmission can be changed by pulling it out from the outside. Pay attention to the depth of the current seal. I tried to use some sheet metal screws and a slide hammer to get my seal out. Wasn't working too well. Went up to the dealer and he had it out in 15 seconds. He used a special puller...Lysle. Brooks discusses it in one of his rebuilds. Probably worth investing in this:

https://forums.bmwmoa.org/showthread.php?73029-Camshaft-seal-replacement
 
You should make sure that the oil has more of a gear oil smell, ie, more sulphur before you start yanking the flywheel, etc. Yes, the input seal to the transmission can be changed by pulling it out from the outside. Pay attention to the depth of the current seal. I tried to use some sheet metal screws and a slide hammer to get my seal out. Wasn't working too well. Went up to the dealer and he had it out in 15 seconds. He used a special puller...Lysle. Brooks discusses it in one of his rebuilds. Probably worth investing in this:

https://forums.bmwmoa.org/showthread.php?73029-Camshaft-seal-replacement

From the look and smell, I am pretty sure it's tranny oil. And thinking about it some more, how would engine oil even get to the transmission input shaft area? Would have to go around the clutch and flywheel somehow.

Since I bought the fly wheel puller, main shaft seal and oil pump o-ring already, I will go in there and replace them. The seal puller tool definitely looks like a worthwhile investment. Wish me luck :)
 
Have we discussed blocking the crankshaft in the front of the engine before the flywheel is pulled?
 
Have we discussed blocking the crankshaft in the front of the engine before the flywheel is pulled?

Yes, many times, but thanks anyways fro bringing it up!

Something else just came to my mind, how do I know if the transmission output shaft seal is good? Darin and measure the cc's of the tranny oil to determine if anything migrated in or out of there?
 
I'd pull it and replace it. Peace of mind. I doubt you'd be able to make a definitive decision based upon fluid measure. Unless you lost 1/2 a liter...then you'd have bigger problems.
 
Oil leaking from fly wheel hole

When I removed the flywheel bolts, oil came out of two of the holes, similar to what Brook Reams shows on his website (credit below the photo). He used "Permatex Ultra Grey Ridgid High Torque RTV Silicone" to fill the holes before putting the bolts in.

Since no oil was leaking with the bolts installed, I am wondering if that is really necessary? Maybe just use a bit of thread sealer instead?

Capture.JPG

Photo credit Brook Reams
http://brook.reams.me/bmw-motorcyle...l-rear-main-seal-oil-pump-cover-cover-o-ring/
 
:scratch Where would that oil be coming from? I don't believe it is a through bolt such that the thread side sees the inside of the engine case. Maybe it's just leaking from the backside of the flywheel or something... :dunno

I suspect that the specs call for a dry torque, that is no lubrication on the threads. If you use a sealant, you'll need to back off the applied torque value as you could possibly apply too much when sliding friction is allowed with the lube.
 
:scratch Where would that oil be coming from? I don't believe it is a through bolt such that the thread side sees the inside of the engine case. Maybe it's just leaking from the backside of the flywheel or something... :dunno

I suspect that the specs call for a dry torque, that is no lubrication on the threads. If you use a sealant, you'll need to back off the applied torque value as you could possibly apply too much when sliding friction is allowed with the lube.

It's definitely not from the backside of the flywheel. It was dry when I took it out.

So it must come from the inside of the engine somehow, but I agree, it doesn't make much sense.
 
When I removed the flywheel bolts, oil came out of two of the holes, similar to what Brook Reams shows on his website (credit below the photo). He used "Permatex Ultra Grey Ridgid High Torque RTV Silicone" to fill the holes before putting the bolts in.

Since no oil was leaking with the bolts installed, I am wondering if that is really necessary? Maybe just use a bit of thread sealer instead?

View attachment 66530

Photo credit Brook Reams
http://brook.reams.me/bmw-motorcyle...l-rear-main-seal-oil-pump-cover-cover-o-ring/

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.
 
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.

Brook, Thanks for the additional explanation! I guess it can't hurt to do what you did, it's a long way to get back to the flywheel bolts if I ever have to! I just put the main seal back in and pushed the flywheel on, so I guess now is the time! I really enjoy your detailed documentations. Very helpful!!
 
Yes, many times, but thanks anyways fro bringing it up!

Something else just came to my mind, how do I know if the transmission output shaft seal is good? Darin and measure the cc's of the tranny oil to determine if anything migrated in or out of there?

Olaf,

Do you mean the transmission "input" shaft seal which is on the front side of the transmission, in the center, or do you mean the "output" shaft seal which is on the rear of the transmission on the left side where the drive shaft bolts onto the transmission output flange?

If you mean "input" seal, be aware that installing that seal requires a way to keep the input shaft splines from damaging the input seal. BMW uses a two piece tool that has a center cup the fits over the input shaft splines and an outer seal driver the fits over the center cup to push the seal home. I have not found that tool at Cycle Works or other airhead tool suppliers. I borrowed one from an airhead mechanic when I changed mine. See my link below on assembling an RS transmission to see pictures of the tool. Note that your 4 speed transmission is different in many ways from the 1977 RS transmission I wrote about.

If you mean the "output" seal, you will have to remove the output flange to pull that seal. That requires a tool to remove the tapered flange from the transmission output shaft. Cycle Works offers that tool.

You can read about how I installed these seals here:

23 BMW 1977 R100RS Transmission Refresh and Assembly

I hope this helps.
 
Olaf,

Do you mean the transmission "input" shaft seal which is on the front side of the transmission, in the center, or do you mean the "output" shaft seal which is on the rear of the transmission on the left side where the drive shaft bolts onto the transmission output flange?

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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