Tech Tips: Wheel Bearings
This tech tip was published in the Vintage BMW Owners Bulletin Vol. 37 No. 2
Removing, adjustment, repacking, and re-installation
Wheel bearings should be checked and greased every 10-15,000 miles. In order to check your wheel bearings, you;ll need to get a special tool called a pin wrench, which is used to remove the threaded bearing seal cover. There are at least two types of pin wrenches commonly used -- the old factory type that is held in a vise, and the other is held by a threaded rod that goes through the wheel where the axle assembly was. They both work well and both have good points to them. For this article, I'll focus on the vise-held old factory type. This wrench has a post in the middle to help center the hub onto the wheel. The center of the pin wrench is small enough to fit the 1974 /6 front axle hole, and has a collar for the later larger axles, and bigger collar for the Earls fork bikes. The 4-hole pin configuration is the same for all of these bikes.
Remove wheel from the bike. Note: On the front wheel you will need to tap out the intermediate bushing with an appropriate tool. Clamp pin wrench into vise. Install wheel (hub cap side down) on pin wrench so that it mates with the holes in the threaded bearing seal cover, fitting onto the pins of the wrench (Photo 1). Then screw out the seal cover by rotating the wheel. The weight of the wheel keeps it aligned onto the pin wrench, and the wheel diameter provides the leverage required to unscrew the seal cover. This is the advantage of the vise-held pin wrench tool. The threaded rod pin wrench tool also unscrews the seal cover but relies on the threaded rod torque to hold the pin wrench in place. You then have to strike the arm of the pin wrench to get the bearing seal to unthread. In doing so, you're also loosening the threaded rod because they unscrew in the same direction but with different thread pitches. (This is why I prefer the vise-held tool).
Once the bearing seal cover is loose enough to remove with your fingers (do not completely unthread it because all of the internal wheel bearing contents will fall out) flip the entire wheel assembly over and remove the threaded bearing seal cover (Photo 2), the hub cap, and the large wave washer. Please note that there are two styles of threaded bearing seal covers. One has a felt seal on the inside, the other has a rubber seal on the outside (Photos 3 and 4). The spacer between the tapered timken bearing and the axle needs to be removed and set aside. Then remove the tapered timken bearing, the internal collar with the spacer, and set them aside on a clean surface.
Next, flip the wheel over so that it is brake-drum side up. Remove the felt seal and separate the spacer out from there. Note: You cannot drive the seal and spacer out through the hub. There is a collar inside the felt seal unit that prevents this, and if you try to force it, you'll break the hub casting.
For the next part in the process, I have been using a /5 or /6 rear axle (Photos-5 and 6) with a front wheel bushing from an Earls fork bike to clamp the whole assembly together, with a spacer for the rest of the axle so that the axle nut can be torque to hold the wheel bearing assembly together to be driven out. Now take your axle from the drum side, so that the threaded side goes down into the wheel bearing assembly, turn the wheel over, and insert the small collar; spacer; and timken bearing and wheel seal spacer onto the axle. Put the axle spacer that takes up the space between the threaded portion of the axle and put your washer and nut together and tighten it like you would to put it back on the motorcycle (Photos 7 and 8). On the brake side of the wheel drive the whole assembly out (Photo 9). I use a dead blow hammer for this so as not to destroy the end of the axle this axle has been in use for over 30 years.
Now clean the whole assembly being careful not to mix the taper bearing assemblies. Once it is clean and dry, look at the bearing shell for unfavorable wear. Also check the roller for the same, and make sure that the rollers are not read y to fall out of the races. Reassemble the whole unit to check for correct amount of play in the assembly (Photo 10). Compress bearing assembly by tightening the nut to same torque as for installing the wheel on the bike. The bearing is properly adjusted when the outer spacer bushing between the two taper roller bearing outer races may, without any side play, with moderate pressure be displaced within the diameteral play. Otherwise install a new spacer and test fit again until it is correct. There are over ten different-sized spacers for this. With wear a smaller spacer is needed. If you replace one or two bearings, you'll have to repeat this process several times until the play is correct.
In layperson's terms this means when the whole thing is torqued together you can spin the assembly with play but still have some preload on the bearings. If you have never done this, have someone you trust show you this - it's a feel thing. With too little play, the rollers will push the grease out the bearings and destroy the bearings; too much play and the wheel will wobble on the axle.
Now pack new grease into the roller bearing assembly then assemble back onto the axle in the same order that it came out of the wheel. To do this, clamp rear wheel axle spindle with soft-metal jaws into vise and install the complete bearing set consisting of left taper roller bearing, spacer washer, inner spacer bushing, outer spacer bushing and right taper roller bearing upon the axle spindle. Then tighten to hold everything in place, align the outside inner collar with the bearing shells; before reinstalling bearings into the hub, check for freedom of play again.
To install the whole assembly back into the wheel hub I like to heat the hub rather than just drive it back in with a dead blow hammer. If done correctly, the whole unit will slide in. Then just a slight tap is needed to seat it. Then replace the felt or rubber seal in the threaded hub ring, the wave washer on the collar of the hub, the hub cap on top, centered, and the bearing seal cover. Start screwing the threaded bearing seal cover by hand, then tighten with the pin wrench. (If this is the front wheel do not forget to replace the inner bushing.)
Note: I prefer to use anti-seize on the threads.