Need help troubleshooting

[bbell1]

Greetings,

I started a restoration project a year ago on an '72 R75/5. And let me say upfront that I'm not a mechanic but have enjoyed rummaging in and on this old airhead. Did something similar to a '84 R65 years a go.

This bike had been in an accident 10 years ago. I've done a complete tear-down and over time have pieced, cleaned, replaced and tinkered where necessary.

I thought I was nearing an initial attempt at starting the bike but now notice that, when I apply the clutch, the rear wheel will neither roll forward or backward (except for a little play). it seems to come up to hard stop, with a clunk, when I try to roll it forward (whileon the center stand). When I put the bike in neutral it does spin freely. I took the heads off to make shure the pistons weren't frozen (new rings) and I can get them to budge, reluctantly, using an allen wrench in the front rotor.

I used a cheater bar to fully depress the clutch arm and stilll no luck with the rear wheel.

So.... Is it the transmission? Clutch? Ideas to narrow down the issue?

Thanks in advance!

 

[RPGR90s]

If I understand you correctly, you're saying that the bike will roll in neutral but when any gear is selected AND the clutch lever pulled in (dis-engaging the clutch), the bike won't roll?

How long has the bike been sitting since you've been working on it?
Did you have it stored on a concrete floor in a cold environment? (think Michigan winter in a garage)

It's very possible that the clutch disc is fused to the pressure plate via rust.

It happened to my R90s many, many years ago after storage in my new garage on a cold damp floor.

Moisture rises up from the concrete and attaches to the steel pressure plate, forming a bond with the clutch disc.

IF that's what's happening, here's how you restore order.

1. Have a buddy available with gym shoes
2. Start the bike in neutral
3. Get on the bike
4. Get your buddy to start pushing you as fast as he can (think push- starting sequence here)
5. When he's reached his top speed, pull the clutch lever in and shift UP to 2nd

The bike will ignore the clutch for a moment, acting as if you've upshifted without using the clutch

Rev the engine with the clutch lever pulled in as this will cause the clutch disc to separate from the pressure plate, leaving the bike in gear and verifying that the bike will roll with the clutch lever pulled in.

Let us know how that works.
RickR90s

 

[dennisdarrow]

Can you upshift into 5th or 4th. While there with the bike on the centerstand, can you with a BIT OF FORCE turn the rear wheel? This is an alternative method of turning the engine over and if the clutch plate IS frozen to the flywheel, it should still turn the engine over. At least this tells us that something isn't locked up in the driveline............

 

[pglaves]

With the transmission in neutral the rear wheel turns. This means the final drive, driveshaft, and transmission output shaft do turn.

The engine turns by hand. Stiffly. Using a little Allen wrench and probably with spark plugs still installed. This sounds normal.

So what is in the middle. The clutch that is not releasing: either because the release mechanism is somehow faulty, or more likely the disk is stuck to the pressure plate/clutch cover. He might break it loose and slip it a bit which will "polish" things somewhat. The better approach is to pull the transmission and clean/fix things correctly. YMMV

 

[69zeff65]

Does the bike run?

If it does you can try the usual things mentioned above to get that clutch disc free. If the bike isn't a runner or if the usual methods don't work I would agree with Mr Glaves that it is best to pull the transmission, figure out the reason and fix it right and once. While your in there you might want to replace the rear engine seal, oil pump O-ring, transmission input shaft seal, neutral switch and clean and lube the input splines. If you haven't done this stuff before it might take an afternoon and some of the next morning but the education you get is well worth it.

 

[cseltz]

This happened to me recently. I got the bike running in 1st gear on my lane, pulled in the clutch and cranked the throttle hard. The clutch plates broke free and it has been fine ever since.

 

[bbell1]

I have not yet tried to start her. Had just noticed the issue as I finished the electrical and was making sure the neutral light, along with the rest of the lights were working. At the point of putting the heads back on, tank, seat, and a little gas. Everything will need some adjustment - carbs, brakes, etc., so would be nice to move beyond this little "opportunity".

 

[bbell1]

Thanks for all the input.

How safe/effective would it be to do this on the center stand with the rear wheel off the ground?

Just curious (lazy).

 

[cseltz]

Thanks for all the input.

How safe/effective would it be to do this on the center stand with the rear wheel off the ground?

Just curious (lazy).

I don't know exactly how you would do it on the center stand. I had the advantage of some mud behind my shop (put it in first with the front brake and spun the back wheel). If you start in neutral, get the bike moving (pushing or coasting down hill) and drop it into first gear, that would work. Make sure you have a bit of room to maneuver just in case it doesn't work but it should.

 

[bbell1]

This has been great info. Bmwrench, you make a good point. I could probably free it but the rust would still be there. I had skirted this can of worms and now it seems I need to backtrack a little, unmount the tranny and clean up the rear of the engine.

Are there any special tools needed? I've looked at these very helpful sites to get an idea of what's in store.
http://brook.reams.me/bmw-motorcyle...ct/21-bmw-r755-clutch-removal-and-inspection/

http://bmwmotorcycletech.info/flywheelremovalwarning.htm

If you know of any other helpful online resources please let me know.

Question - do I need to replace the drive shaft 12 sided bolts after I remove them?

Again, thanks to all for the sage advice!

 

[20774]

Question - do I need to replace the drive shaft 12 sided bolts after I remove them?

A shop mechanic would change them because of insurance reasons. The bolts (not the long ones with the lock washer...which are no longer used...but the shorter ones) are stretch bolts and potentially could get deformed during installation. However, the degree of stretch is not really into the plastic deformation range, but really just elastically stretched...that's what provides the holding power so they don't back out. You can test each bolt by running the bolts into the output flange of the transmission...if they feed fine with your fingers, they have plastically deformed. Specs call for 29 ft-lbs...I've typically used the tool kit wrench and a rag in the palm of my hand and gave it as good of a grunt as I could. I also use some blue Loctite on the threads.

 

[bbell1]

Here's the latest. I decided that I'd go ahead and take off the tranny mainly because I've come to realize that with this project, I'll need to install and then remove, each and every piece, at least three of four times. Since I had only installed the tranny once, it was time to uninstall and then get to the clutch plates.

I thought you might want to see the rust build up that I found and to confirm each and all of your spot diagnosis. Well done and thanks! I'll start to clean these up and see how they look.

Again, I appreciate all the insight and help.

Cheers.