Vintage BMW Motorcycle Owners

Craig,
I'm confused about the picture of the plastigage. Don't the bearings have to be on the shafts to measure end play?
I'm using the Cycleworks measuring plate to calculate clearance. The Cycleworks thickness putty involves heating the entire transmission up in the oven, so that's not going to happen in this house! I've used plastigage before for auto main bearings but never really trusted it.
I'm very interested in what fixes the 1st gear clunk.
-Randy

Randy;
Yes. To measure the end play you have to reassemble the box with plastigage between the shim and the gear, then dissemble the box again to read the clearance. and yes it is a bit tedious.

Jim;
You may be right. I ran into a old friend over the week end. He used to run a BMW shop down near Greensburg, PA. He said the little bit of wear on those dogs might very well be enough to cause the slipping.

Craig

Craig,
If what I'm seeing in the picture is the washer that goes between 1st gear and the bearing it shouldn't at all figure into the shimming.
The washer goes on the shaft then the bearing gets pressed onto the shaft against that washer. So there should be zero space there.
I would put the plastigage on the outer race of the bearing and see what clearance shows there when the rear cover gets cinched down.
-Randy

The site will not let me respond.

I have tried several times to reply to your post but the site keeps giving me an error message.

What you are calling a washer is actually a shim. The gears on the output shaft rotate at different speeds or ratios. They are only "locked in" when engaged by the dogs. There has to be clearance between them so the gear oil can lubricate them and keep them from binding. What I call "end play" the Haynes manual calls "axial float". It is the sum of the clearances between all the components on the output shaft. Haynes says that should be 0-0.1 mm. What I measured with the plastigage showed >0.1 with 1 shim in the line and 0.05 mm with 2 shims in the line (within spec.).

Craig

This is my first time through the gearbox so I'm trying to learn. The Haynes manual I have calls it a "thrust washer". There's another one in front of the first gear also.

The clearance I'm referring to is the clearance between the rear 3 shaft bearings and the rear cover. That's supposed to be between 0.05 and 0.1mm according to Cycleworks, and Boxer2valve is similar. My guess is that's just to make sure the shaft bearings have some wiggle room and don't bind up.

I'll try using a short piece of plastigage across (radially) the shim at the four quadrants to check the clearance. The OD of the shims is ~50mm and the width is only ~4mm. The reason to lay the plastigage ACROSS the shim is if it squishes out more than 4mm, I'll still be able to read the width.

I'm still waiting for a press to press off the 1st gear on the intermediate shaft so this is just another extended period of bike downtime...

I think you're reading the manual wrong. The bearings are basically pressed into the end cover of the case. All the motion is internal to the bearing. Haynes recommends heating the case cover to 100 degrees C (to expand the metal) before putting in the bearings. I believe the 0.05 to 0.1 mm clearance refers to the sum of clearances along the shaft.

BUT -

This is also my first time inside the gearbox. and I have 2 apart at the same time. Right now I'm learning how to get the shifter camplate and pawl aligned on the R 75/5 (bad bearing), and it looks like I'll have to replace 1st and 4th gears in the R 90/6.

The intermediate shaft (cluster shaft) looks to be a single piece. (it is in most cars). I'm not sure you can press 1st gear off.

Craig

Craig,
You should look at William's video from Boxer2Valve. Go to:

https://www.boxer2valve.com/gearwheel-l ... -gear.html

Scroll down to "VIDEO" and he has two rebuild YouTube videos. The second one has his shim measurement and calculations.

Both videos are worthwhile.

YES that was a very useful video. THANK YOU.
I notice he also called the clearance measurement "end play". His method of measurement required adding the thickness of bearing races and bearing seat depths. I think it is basically the same measurement I was making, only in a different location. Plastigage measurement work best on flat surfaces, so I made the measurement between 1st gear and the thrust washer where flat surfaces are easy to get to.

On a related subject I think I'll replace the clutch. What do you think? Craig

Miles on the clutch? Thickness of clutch disk?