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K100 Rear Wheel Bearing Replacement.


RFW

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Recently (and probably for the first time since I owned the bike for 3-1/2 years now), I checked the play in rear wheel bearings in my '86 K100RT. Measured at the rim, I get about 0.020" side to side play.

 

Although the Haynes manual is no help in this, It seems to me that this is more than is should be.

 

I have two questions: First, is this "normal", and is it acceptable?

 

Second, where can I find some details on replacing the rear wheel bearings? I have rebuilt automotive differentials before, so this is not new to me. But I'd like to get some specifics on the procedures for this bike, such as the correct procedure to adjust the bearings and the correct positioning of the crown gear versus the pinion.

 

Has anyone done this before, or can anyone suggest a source of info?

 

Bob.

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duckbubbles

My '85 K100RS has over 300,000 miles on the original rear end and has no discernable play side to side. First make SURE that the wheel is torqued to spec. They have been known to get loose and come off! Then check for freeplay at the swingarm pivots. There are plastic caged tapered roller bearings that can get loose over time. If these checkes are good and you still have play there, it may be time to get into the rear end. Also don't forget to check the torque of the rear end mounting to the swingarm.

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My '85 K100RS has over 300,000 miles on the original rear end and has no discernable play side to side. First make SURE that the wheel is torqued to spec. They have been known to get loose and come off! Then check for freeplay at the swingarm pivots. There are plastic caged tapered roller bearings that can get loose over time. If these checkes are good and you still have play there, it may be time to get into the rear end. Also don't forget to check the torque of the rear end mounting to the swingarm.

Thanks, but the wheel is in tight, and the swingarm bearings have no play (I adjust them yearly). The play is definitely the bearings... You can feel it if you stick your finger between the brake disk and the drive housing, and have someone try to wiggle the tire from side to side. The play is very little, but it is perceptible.

 

The mounting bolts for the rear drive are also nice and tight.... I just did a spline grease job not long ago.

 

Interestingly, when I check it after riding to work, and the drive is a bit warm, the play all but disappears.

 

I'm about to go on a road trip in a week (maybe about 1000km) so I'll be keeping an eye on it.

 

Thanks for the suggestions.

 

Bob.

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duckbubbles

My Haynes manual seems to give a pretty good account of the rebuilding of the rear end. Check the shims really carefully for wear. I have run synthetic oil (gear lube) in the rear end for the last 250K miles. It will probably not give you any problems for a while, unless you travel really loaded down. Good luck.

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My Haynes manual seems to give a pretty good account of the rebuilding of the rear end. Check the shims really carefully for wear.

I have the Haynes manual. Other than listing the gear lash, and bearing preload, there is nothing that hints at how you do this when the rear drive has to be bolted up tight to measure it!

 

At least in a car's differential, you have access to the gears! In any event, the shims don't wear, since they are under heavy compression. The problem is that new bearings are slightly different in thickness, thus requiring different thickness shims. This in turn requires some way to measure the preload and gear lash to verify the shims are indeed correct.

 

Probably I'll have to do it the hard way, which means assemble the thing, with prussian blue on the gear teeth, then spin the gears, then disassemble it and check the tooth contact patches, then repeat and repeat until it is right! frown.gif

 

But I'm still not sure how to measure the 0.05~0.10mm bearing preload, when I can't even get in there to measure it! Probably I'll have to select a set of shims that JUST results in a perfect fit with no preload but no play either. Then use a shim that is 0.05~0.10mm thicker

 

Bob.

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Bob,

There is a special fixture (33 2 601) for measuring the bearing and determining the tapered bearing preload. You are ONLY affecting the preload on the bearings, NOT the gear mesh. The pinion/ring gear mesh is set by varying the spacer on the 'other' side of the ring gear. You have not changed this relationship. Unless you removed the pinion gear, the depth hasn't changed there either.

I'd go for the zero clearance + 0.05mm shim. Forget the prussian blue. smile.gif

 

Mick

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Bob,

There is a special fixture (33 2 601) for measuring the bearing and determining the tapered bearing preload. You are ONLY affecting the preload on the bearings, NOT the gear mesh. The pinion/ring gear mesh is set by varying the spacer on the 'other' side of the ring gear. You have not changed this relationship. Unless you removed the pinion gear, the depth hasn't changed there either.

I'd go for the zero clearance + 0.05mm shim. Forget the prussian blue. smile.gif

Thanks for the fixture reference. Actually, I already figured out that the shim under the tapered roller was for setting the gear lash, then once that was established, the shim next to the big ball bearing is then adjusted for bearing preload.

 

You are probably right... prussian blue is not needed. Since the pinion is not changing, selecting a shim that results in the correct gear tooth clearance will automatically put things back where they should be. No need to obsess about tooth contact patch location.

 

Of course this still leaves the problem of measuring the interferance fit of the bearing, since I suspect that the special fixture you mention is probably cost-prohibitive. But this just means spending a little more time to do this the hard way, and I have the time grin.gif

 

Again, thanks for your comments.

 

Bob.

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