'82 gearbox

[John Roberts]

The gearbox on my '82 R100RS has been getting noisier for a few thousand miles, I know perfectly well that I should have done something about it a long time ago, and now I've decided not to use it again until I get off my back side and fix it. Other than the whine there are no other symptoms.

So, two things:

What damage can I expect to find other than to the bearings- can I expect damage to the bearing seatings and to the gears?

Where can I hire the measuring plate for the shims?

I downloaded instructions from the HUBB a few years ago on how to strip this gearbox, it was based on a demonstration to a group of bikers and included a lot of very good photos. Does anyone know which one I mean, and where can I find it on the web?

Thanks.

[Carl P]

Not what you were looking for but might help.

A Tale Of Two Transmissions - Airhead Style - ADVrider

Much more on ADVrider if you search for trans or transmission in "olds cool".

[dc lindberg]

When you open the gearbox, you will see on the hypoid sprockets whether or not you have the old or new angulation.
The new, 17.5', came in april 1982.

Problem you may encounter is pitted sprockets... usually the hypoid sprockets... => new sprockets -

17' - non-X:ed, were more prone to get pitted.

17.5' - X:ed, seems to last much longer.


ALL sprockets are available individually, though BMW does not retail as individual spareparts... but, these can help you:
e.g.:
Motoren-Israel
hpn
Siebenrock - BMW Motorräder & Teile ...alles ab /5
Moto-bins - BMW Spare Parts and Accessories for Motorcycles - Index
Motorworks - BMW Motorcycle Spares - home


Consider:
* lower 1st (more expensive to change - perfect in heavy trafficjam and off-road)
* higher 5th ("simple" to change - full gearshift up from 4th to 5th instead of 4 to 4½; perfect on the freeways).
HPN-Motorradtechnik GmbH - Germany
HPN-Motorrad: Engine & Gearbox
Motoren-Israel
BMW Bayer - BMW Motorräder & Teile ...alles ab /5
Moto-bins - BMW Spare Parts and Accessories for Motorcycles - Displayfinal

Nylon roller vs ballbearing in the shifting mechanism... I truely can not say which is best. Nylon roller is softer, whilst the ballbearing is smoother and more distinct still it "jams" as on shifts which the nylon roller does not untill it gets worn down and then it becomes a menace...
Moto-bins - BMW Spare Parts and Accessories for Motorcycles - Displayfinal

Install new returnspring!

Now for a thing you will not find any mentioning of anywhere in the overhaul litterature:
- measure all taps, shafts, axels and centers.
See, when an airhead gearbox is hard to shift or too noicy it is probably due to a missmatch between the parts. Referenses: "Ask Oak" and "Snowbum" at Airheads Beemer Club - Home .

[Enprize]

There are several good shops that will do the correct rebuild. I had Oak do mine at a cost of $1200. Ted Porter, Montana Bob (Bob Clements) are two that I'd suggest. The one thing you don't mention is the mileage. If high mileage and you get quotes for less than $1000.00 they are lowballing you and you should be careful.

james

[dc lindberg]

How did it end?

[John Roberts]

Originally Posted by dc lindberg

How did it end?

Sorry, Albert, I've only just seen your post.

Yes, all done and dusted. I borrowed all the tools from the BMW Club, it was so nice to have the correct ones and not have to resort to making do.

As it happened all their measuring plates were out on loan but I was offered an old one that was supposed to have something not quite right with it, but the Tool Hire Secretary didn't know what exactly, as I have the dimensions for the plate (thank you Joerg) I could check it before using it so I went ahead and used it.

All seemed OK with the plate apart from the clearance around the bearings, from memory they were three thou (that's IMPERIAL, I'm still in the dark ages and so still not used to metric) larger than the bearing outer races. In fact this clearance was in accordance with Joerg's drawing but I found it to be very inconvenient because it allowed the outer race to tip while measuring the protrusion of the bearings through the plate. I managed to get around that by putting a dial gauge (dti) bearing lightly on one side of the protruding race to ensure that it didn't tip up (or, more to the point, to make sure that I wasn't pushing the side I was measuring down) before measuring on the side opposite with a depth micrometer bridgeing two hardened steel parallels. I took photos of the setup but although the pictures display OK on the camera screen I can't download them to the computer. It's a fault on this particular memory card, I'll try and post them ASAP if I can get it sorted.

For that reason I would be very interested to know what is the size of the three large bored holes in the plate for the bearings in a factory supplied measuring plate if anyone can help, I would be interested to know whether the bearings are held snugly enough in the bores so as not to tip when measured.

Anyway, after taking dozens of measurements and averaging them out I found that the shimming would be identical for two of the new bearings and the other one should have the 0.38mm + 0.28mm instead of the 0.20mm + 0.50mm shims. On reflection, considering that I hadn't replaced any of the shafts, I decided not to change the shimming and left them as they were, the truth is that bearings are manufactured to a precision way, way beyond my ability to measure so any variation in the bearings themselves would be negligible.

All that was about 3,000 miles ago and there have been no problems, it changes gear just like before- no better or worse, but the noise has gone.

Oh, the reason for the original noise was that the front end of the output shaft bearing had broken up, if I can I'll post a photo of that too in due course. I replaced all six bearings though, it seemed silly not to.

[dc lindberg]

Hi John,

Great that all is well now!