I am just after the spec for the front and rear wheel bearings for my '88 K75.
Anyone happen to have them to hand?
Thanks.

BooG,

The standard size front wheel bearing for the K100 & K75 is 25mm x 47mm x 12mm (Haynes manual), however, the K75S changed to a three spoke wheel design from 1991 onwards and that seems to have a different size bearing on RHS (25mm x 47mm x 16mm). Don't know if you have the standard wheel of the 3 spoke type.

Some more details at:
https://www.james-sherlock.co.uk/component/virtuemart/?page=shop.browse&category_id=366

I bought a pair of wheel bearings for my K100 front wheel, but keep shying away from fitting them because I don't have a slide hammer or other puller to extract the old ones and no easy means of heating the wheel to 100 deg C to fit the new ones. Both Haynes & Clymer manuals talk of difficulties due to a very tight fit in the hub. Maybe this will be a job for my local bike shop when I need a new tyre!

The rear wheel has no bearings - it is bolted directly onto the flange of the final drive crown wheel. Providing it is mounted securely, any play in the rear wheel will be due to worn bearings in the final drive assembly itself and that's a different game altogether!

Go to www.realoem.com and search for your bike and for the appropriate page with the wheels you have on your model, Y spoke or three spoke. The catalogue will often show the industry standard number as well as the dimensions of the wheel bearings, left and right.

In the states the front wheel bearings are very inexpensive from a BMW dealer.

"I bought a pair of wheel bearings for my K100 front wheel, but keep shying away from fitting them because I don't have a slide hammer or other puller to extract the old ones"

The tubular spacer between the wheel bearings is located to centre by 2 thin metal collars.  If you put a large screwdriver through one bearing with the end about half way to the other and give a good heave sideways the thin collars will collapse and you can get at the bearing on the other side to knock it out, then knock the other out and straighten the collars and then I grind part of the tubular spacer away so that next time it doesn't need to bend the thin collars.

RicK G wrote:"I bought a pair of wheel bearings for my K100 front wheel, but keep shying away from fitting them because I don't have a slide hammer or other puller to extract the old ones"

The tubular spacer between the wheel bearings is located to centre by 2 thin metal collars.  If you put a large screwdriver through one bearing with the end about half way to the other and give a good heave sideways the thin collars will collapse and you can get at the bearing on the other side to knock it out, then knock the other out and straighten the collars and then I grind part of the tubular spacer away so that next time it doesn't need to bend the thin collars.

Thanks Rick - I do keep considering the "brute force & ignorance" route. The bearings I want to change (only slight play in them) are in my spare front wheel but it still has a few 1000 miles of tread on the tyre and remains useable. Sods law says that if I start butchering the bearings, I'll need it as a spare and I'll regret it. 

I do like a challenge though and your description removes some of my ignorance from the equation.

RicK G wrote:The tubular spacer between the wheel bearings is located to centre by 2 thin metal collars.  If you put a large screwdriver through one bearing with the end about half way to the other and give a good heave sideways the thin collars will collapse and you can get at the bearing on the other side to knock it out, then knock the other out and straighten the collars and then I grind part of the tubular spacer away so that next time it doesn't need to bend the thin collars.

I've read this is another method to remove wheel bearings without a dedicated puller.

Get an expanding bolt/Loxin/Dynabolt and expand the end of it into the bearing.  Then use a punch to drift it out from the other side.

So for this size, you will need a 25mm Dynabolt.  Not sure how easily they are available.  Most hardware shops probably go no bigger than maybe 16mm? 

And a heat gun/paint stripping super hairdryer should give enough heat to heat up the hub to help release the bearing.