On my last project I replaced the wheel bearings but left the tyres as they were pretty good, but on the 75/5 I really wanted to completely rebuild the spoked wheels. The old spokes were badly corroded and I didn’t think they would be able to polish up that well. The tyres were also very old, cracked and didn’t have much tread on the edges.
I’ve never changed the tyres on a motorcycle or rebuilt a spoked motorcycle wheel, however I have done both those jobs many times on bicycle wheels so how hard can it be right? It ended up taking most of a weekend.
I started by removing the old tyres and tubes. This requires some kind of tyre levers (I got some from eBay) and some good protectors for the rim. It also helps immensely if you heat the tyre up first (I used a heat gun) and make sure the tube is completely deflated and the tube nipple retaining screw is removed. I don’t have many pictures of this process but it takes a fair amount of elbow grease and some swearing- break the bead all the way round both sides of the tyre and then introduce the tyre lever under one side, using the rim protector for levering on. Then work your way around and lift the bead of the tyre off the rim. Then flip things over and kinda lever the rim out of the tyre. If the tyre is warm enough you can often just pull it out. When the tyre is off you can remove the rim tape underneath which covers the spoke nipples.
Once the two wheels are out, remove the hubcaps from the left hand side (the non brake side) and set them aside. The same bolts that hold the hubcaps on also hold the oil/grease seal holders on and these may come loose. There is a top hat (thrust sleeve) stuck in them so keep an eye out for that. On my front wheel the sleeve reducer, outer top hat thrust sleeve, seal holder, paper gasket and inner bearing cone and wedding ring spacer all came out- don’t worry this is normal but replace the inner bearing cone in the outer race before proceeding as it makes it easier.
Next step is to remove the old bearings. I did this working on a bench. The idea is that you remove the two bearings and all the sleeves etc as one package. I followed William Plam’s video on Boxer2Valve which is excellent. The rear axle is introduced into the hub from the brake side (the wrong side) and some kind of spacer applied to the axel on the other side which allows the nut to be replaced and some pressure kept on the contents of the hub. As a spacer I just used a piece of stainless steel pipe. The hub is then heated up with a heat gun on both sides until it’s around 75 degrees (centigrade) and then a moderate tap on the brake side end of the axle should knock everything out as one package as shown.
When you remove the axle take a note of the order and orientation of all the parts and take some photographs. There is a really good picture in Duane Ausherman’s page about wheel bearings. There are two grease seals to remove- on in the hub on the brake side and one in the seal holder on the hubcap side. These come out with a standard seal puller but take a few photographs of them as there are a million different BMW wheel seals and you will want to get the correct replacements (they say you shouldn’t reuse the seals)
After removing the bearings front and back I went ahead and removed the spokes. To do this I sprayed everything with WD40 and let it soak. Then I used a special tool- a screw driver with a slot ground in the end to remove the nipple from the spokes. When the hubs and rims were apart the hubs were taken for vapour blasting and the rims cleaned up with 600g sand paper followed by 1000g and then Autosol aluminium polish and 0000 steel wool.
Replacing Bearings
Now it’s time to rebuild- first I replaced the bearings mainly because it’s easier to heat the hubs up while they are not attached to rims (cause they fit in the oven!) and you really have to get the hubs hot for this part (at least 100c). Holding the rear axle in a vice put the components back on as they came out- that is inner thrust washer (small top hat), brake side bearing cone and cup, inner and outer centre spacers, wedding band spacer and then outer hub-side bearing. To get the bearing preload in the right ball park adjust the thickness of the wedding band spacer- either by having a whole heap of these in 0.05mm increments (who has that?) or by using 0.05mm shims in a shim kit. I got one from CycleWorks. Add thickness and then use your spacer (piece of pipe) to do a trial of torquing the nut. Feel how tight things are- you should be able to move the outer centre spacer with moderate thumb pressure and the bearings should spin well. Err on the side of under-tightened. When you have a package made up with about the right thickness of spacers then you are ready to put the lot back into the hub, in a reversal of the removal process. Put the hub in the oven as hot as it will go for about 15 minutes and put the bearing package in the freezer. When the hub is hot the package should be able to just drop in from the hub side- there should be no tapping needed. Then let everything cool down.
Next entry will be about rebuilding spoked wheels! Stay tuned…
