k75RT final drive taper bearing preload shimming

[Barrieb]

So, after being assured by the PT that the driveshaft had been furnished with a new splined end, and a number of other works.  I decided it would be best to take a quick look, check and lube as required.

Uh oh, Splines are triangulated on both shaft and final drive.

Now over here in the UK, we can get the shaft “slugged” With a new splines end for about $120, which seems reasonable.

on to the final drive: on the same day I bought this bike, I also bought a high mileage donor bike with literally a shed load of spares.  This came in useful as I needed a new fuel pump, holder and gauze filter (old petrol is really nasty to rubber!)

With the spares came a disassembled rear unit, which the PT had been working on trying to get the crownwheel bearing off.
The splines on this unit are spot on.
But somewhere along the way I have misplaced the large spacer that determines the taper bearing load. ☺️

I have read the workshop manual taken from this site, but it’s not very clear how to get the actual calculation to get to the shim thickness.

Any help from someone who has had to do this greatly appreciated

Thanks

Barrie

[Laitch]

Why was the PO trying to remove the crown wheel?

The tapered bearing has been removed and you misplaced its shim? If you find that shim, you likely won't need to measure even if you replace the bearing, from what I've read by knowledgeable sources. How's that for an inducement to restart the hunt?

Airmonger, a member here, was a BMW mechanic in the eighties. Send a personal message asking for an opinion concerning your dilemma. Maybe somebody else will chime in soon. It's a technical project that requires a gauge and a few special tools as you may already realize. I haven't needed to do it yet and probably wouldn't if I could find a decent assembled replacement in the aftermarket. 

Good luck with this project.

[The Mighty Gryphon]

I wonder if Plasti-Gage would help you figure out the shim size needed.

[Barrieb]

Thanks guys,

The PO was trying to remove the large output bearing, my understanding that was the issue with that drive (this was a spare part he was working on)

The taper bearing has never been removed, so the bevel crownwheel shimming should be fine.

What’s missing is Large the shim/Spacer that sits between the outside of the large outer crownwheel bearing and the final drive cover.

There are 17 different sizes on the BM parts list ranging from 0.1mm to 1.7mm to ensure correct pressure on the taper bearing

That original spacer is not going to turn up ☹️ I’m embarrassed to say.  I’m not aware of anyone in the UK, who would rebuild this?

It would be great to get a new input seal put in and this spacer done.  I’ll take on most jobs, but taking apart the input area of the final drive looks like it needs the proper gear, same with measuring to get the spacer correct.

I would imagine BMW in
Peterborough would charge me an arm and a leg

Barrie

[Barrieb]

Any final thoughts on this before I hand over cash for secondhand unit please?

[Arktasian]

I'll pitch in.
I haven't worked on that final drive, and not aware what the basic size of the spacer is. However, there are cheats that one can use to get "in the ball park" size wise - including use of solder wire segments placed with some tacky grease where the spacer might reside and assembling. On taking apart you can mic the squished solder to gain an idea of spacer dimension. Those must be relatively cheap to purchase (from Motobins, or similar), just purchase a few either side of & including the measurement and assemble the rdu to then measure preload and rotational resistance. Small units like this wouldn't need to offer more than slight resistance (perhaps 5-10 in/lbs) with a used bearing, slightly more when renewed. Guess is depends how much a replacement set would cost you, and timing, and your interest to pursue.

[Laitch]

Any final thoughts on this before I hand over cash for secondhand unit please?

The first sentence in your opening post of this thread indicates a potential problem that has been encountered here previously. If the condition of the splines on the driveshaft differs significantly from the condition of the splines on the final drive pinion gear, it's possible their coupling will damage both parts after use of some length. This circumstance is the exasperating Achilles heel of the monolever drive system.

Buying a matched pair—driveshaft and final drive—is the preferred strategy but it will take diligence and patience to find one. Replacing the pinion gear on your working drive is a second option so that its condition and the driveshaft condition are alike. The third option is finding a rear drive with splines in good condition and hoping for the best.

Mighty Gryphon's and Arktasian's suggestion are possibilities, too. If you undertake them you will likely learn some valuable lessons in procedure and patience.

[Barrieb]

Thanks guys, both very useful information.

It seems with these splines, on both driveshaft and final drive side, they are always either in perfect (kept lubed) condition or triangulated with significant play and on there way to failure.

In an ideal world, I would get my original drive splines built up and the input seal replaced (output seal and bearing I can do)
And then get the driveshaft ‘slugged’ with a new splined end.
Unfortunately we don’t have an option in the UK for final drive/spline rebuild - correct me if I’m wrong

I will try the solder measurement option and learn as much as I can about final drives and follow the advice given, replace the output seal and bearing and monitor the input seal performance

At the same time get a new end for my driveshaft, if there is no Play at the spline joins and I keep them correctly lubed and monitored, this will get me back on the road.
Keep fingers crossed for me, when I get the gearbox off!

4EAAC69C-B338-433E-AA69-6A07FDBB939C.jpeg (50.84 kB . 625x467 - viewed 366 times)

[Laitch]

It seems with these splines, on both driveshaft and final drive side, they are always either in perfect (kept lubed) condition or triangulated with significant play and on there way to failure.

My observation is that some splined couplings wear significantly slower but they all wear to some degree even if maintained.

Mitigating the speed of wear seems regulated by these conditions.

• using lubricating paste of the correct quantity at appropriate intervals on thoroughly cleaned and dry spline surfaces,
• operating the engine without lugging the transmission,
• smooth clutch engagement and throttle control
• the hardness of the splines,
• whether the spline shafts are 16 or 20 tooth,
• riding on pavement relatively free of defects.

I ride some rough gravel roads for a few thousand miles a year. Despite rear drive spline lubrication at 6,000 mile intervals, the splines have started to develop sawtooth profiles. Maybe I should get a KLR650 or an F800GS, but at highway speed vibration is a consideration. An R1200GS is larger and heavier than I want even if I could afford one. The K75 rides so smoothly when I'm on the highway that I'm not willing to look elsewhere, yet.
Please keep us updated regardless of the direction you pursue solving this condition.

[Barrieb]

Thanks all, here’s the plan:

Either way I need a repaired or new Driveshaft, and the final drive I am looking to shim, is a spare unit so initially I’m not going to get a “matched set”

I picked up a final drive unit, last night for $100, with very good splines, and smooth running, not too loose or tight, also Came with an as new brake disc, so worth the 150 mile round trip!

I’m planning to repair one of my driveshafts, with new splines - I will have to pick the best one, this is going to be based on the UJ as one of my shafts has a notching feel in the central position and I believe it should be totally smooth in all directions with NO free play at all

This will get me back motobricking, with regular checking of the spline lubes etc

I am interested in repairing the Final Drive as per this thread, but how do I measure the torque applied to the taper bearing by the shim (once I have done the solder trick and worked out central size) is this done by attaching a low range torque wrench to the input splines???
I will have the ability to compare one without the shim and a couple of others I know are correct -  hope it’s not a stupid question

Final Laitch: you might surprised by the lack of vibration on the single cylinder BMW,s, really smooth and learn all about not lugging an engine! I had the cheapest one, the Rotax engined F650, last year, but I really felt the engine was quite fragile, with too many things wearing out by 45k
Ironically, I had to strip the complete engine and replace the gearbox output shaft as previous owners had not lubed the shaft and kept the o ring behind the sprocket in good condition.  The circlip holding on the sprocket is not a problem if you do both those things, despite what you read.

Will update on how I get on with the K75’s transmission - but I still love my brick!

[Laitch]

I am interested in repairing the Final Drive as per this thread, but how do I measure the torque applied to the taper bearing by the shim (once I have done the solder trick and worked out central size) is this done by attaching a low range torque wrench to the input splines???

If we accept that the assembly instructions in BMW's manual are complete then preload seems to be based solely on correct measurement to establish the appropriate shim thickness then correct assembly of the shim with other components.