Wheel Bearings

[rinkydink]

Bike is a 76 R90/6 with 20k miles. I am the third owner and am wondering if I should do some preventive replacement on the wheel bearings. I have had no problems with them to date but am I living on borrowed time? I have refurbished/replaced almost everything on this previous garage queen and just wanted to know. TIA

[ME 109]

First thing would be to pull the bearings and clean the outer races and clean the inner race. Once everything is clean you can inspect the outer races for wear. These tapered bearings are capable of many thousand miles if they are cleaned and regreased at each tyre change. More often depending on whether ones rides through water etc etc.
Bearing life is also heavily dependent on having correct bearing pre-load.

[Ken in Oklahoma]

Duane Ausherman has educated a lot of people here (including me) about the (Timkin) tapered roller bearings used on our airheads. A visit to his website in the bearings section will be illuminating.

http://w6rec.com/duane/bmw/wheel_bearing/

Once the principle of our airhead bearings is grasped you will start feeling very comfortable around them. For you it will be particularly important to discover how to remove the bearing "stack" from the rear wheel. Also you will be disappointed to learn (if you haven't already) that different spacers (wedding bands) are needed for preloading the bearings. But, having said that, far more often than not, if the preload was correct, the old spacer is the same one needed for the new bearings. Duane used to sell thin shimming washers that could sometimes be used if a thicker wedding band was required. I don't know if he still does that. Otherwise you'll have to "guess" the thickness wedding band you need and order it. (You will need a micrometer or a set of digital or dial calipers for measurement.)

While the principles of the BMW Timkin bearing stack seem rather complicated I've figured out how to relate it to a car bearing. Most of us have replaced the Timkin bearings on the front spindle of the older cars. And you know that the bearings are adjusted by tightening the spindle nut until all of the clearance is removed and then tightening or loosening the castellated nut until the hole in the spindle is in alignment, and then inserting a cotter pin.

Now imagine that, instead of inserting a cotter pin, you insert a sleeve over the spindle which separates the bearing inner races. The sleeve will be a precision length such that when the nut is tightened, the proper reload is attained on the bearings. That's the principle and you just have to mentally correlate the BMW hardware with the automotive method.

And whatever you do, when removing the stack from your rear wheel, or "pressing" an outer race into bare aluminum you must be sure to heat the hub properly. As Duane points out, removal of any aluminum there can be very expensive metal indeed.

Seriously, when you "get it" on the bearings, you feel empowered.

Ken

[Major Softie]

And all that talk about bearing replacement is something you likely won't have to yet deal with, but you should definitely do the clean and lube deal

[Ken in Oklahoma]

But Wait, There’s More

I have found an easy way to determine if the preload is right on our airhead wheels with their tapered roller bearings. Duane Ausherman has talked about his “shake the wheel” testing on the bike. This is the way I like to do with the wheel is off the bike.

With the wheel on the bench and fully assembled all you really need is a threaded rod and a couple of nuts. I use a spare airhead axle (17mm) with some home made spacers. But a length of 5/8" fine threaded “All Thread” rod and a couple nuts and flat washers would be perfect. I slide the threaded rod where the axle goes and put a flat washer and nut on each end. (It’s immaterial whether you choose to use the “top hat” external spacers because they are outside the bearing “stack”.) Now, using your fingers, you’re going to tighten the two nuts until the clearance goes away.

The feel you’re looking for is not unlike tightening the spindle nut on the front of an old car. As you run the nuts by hand on the read the bearings will be too loose. It’s easy to see and feel since the tapered inner races will wiggle with sideways pressure. There will come a point where the “wiggle” goes away and it feels like the bearing clearance might be taken up. At this point I will grab a couple wrenches, not because I need a lot of torque, but because I need more than my fingers can provide. What you’re going to do is to turn the nuts going from loose to the point where all of the bearing stack clearances are taken up, and then go a little further to evaluate.

What I do is to rotate the threaded rod itself with my fingers with the nuts loose. It won’t rotate totally free because of the heavy weight lube on the bearings. You should be able to see that the bearings have not seated yet, that is, the stack is slightly loose. You keep “tightening” the nuts now gently with the wrench until the clearance goes away. You also keep turning the theaded rod with you fingers to feel how easily it tuns.

(During this procedure I would say not to use more than 10 ft-lbs of guestimated torque on the nuts. You won’t need more to make a determination.)

If the clearance doesn’t quite go away that’s your clue that the inner wheel spacer with wedding band is too long. You’re going to need a thinner wedding band.

Just as likely is that the clearance does go away. What you’re going to do is to feel the tightness of the bearings by rotating the threaded rod with your fingers, then apply a little more torque to the nut with the wrenches. What you’re looking for is the point when additional tightening of the nuts with the wrench does not make the threaded rod harder to turn with your fingers. That means all of the slack has been taken out of the stack. What you want to determine now is whether additional torque to the nuts will make the threaded rod harder to turn with the fingers. If additional torque on the nuts doesn’t result in a harder to turn threaded rod that tells you that the stack has bottomed out and the bearings are preloaded to some degree. If, on the other hand, more torque on the nuts makes the threaded rod ever harder to turn, that tells you that the stack hasn’t bottomed out and you’re going to need a thicker wedding band.

Once you develop the “feel” it will be evident where you stand on wedding band thickness. (Keep in mind that on the bike tigtening the axle nut does put a lot of pressure on the bearing stack. But you’re not going to need anything near that much “tightness” to make your evaluation.) The next trick will be to judge how much thinner or thicker wedding band you need to buy. I would use a micrometer or caliper to measure what I had and order the next two thicker or thinner sizes I figured I would need.

If you need a slightly thinner wedding band than the one you have you might want to try honing the sides of the wedding band on a whet stone (preferably something like a coarse diamond whet stone which is really pretty fine). If you go this route you must be very careful to keep the sides of the wedding band parallel to each other. Often there are machining marks they will serve as a rough guide. I would also want to use a micrometer (not a caliper) to ensure that I’m keeping the sides parallel.

The impact of not keeping the wedding band sides parallel is that it becomes more difficult to determine when all the clearance is taken out of the bearing stack. The bearing stack now has more “spring” to it.

If you should happen to have one of Duane’s shim kits you can, in effect, make a wedding band thicker.

Years ago, when I figured I was going to be in the airhead business for a while I bought a small assortment of wedding bands to keep on hand when I needed them. Unfortunately there are a lot of different sizes available and they are not inexpensive. As I recall I called the size I had in my hand “normal” and ordered a couple or three sizes thinner and thicker. So far I’ve been able to handle my needs with what I have on hand. And as I mentioned earlier, often the size I took out when changing bearings was the same size I needed for the new bearings.

If anybody who comes to the Boxerworks rally at my place in a few days wants to see it, I can demonstrate.


Ken

[rinkydink]

Thanks for the replies. Great stuff Ken, I have some work to do. I have owned the bike since 12/09/2001. They haven't been looked at since I've owned it....maybe 4 tire changes. I'm a bad bad bad man.

[Major Softie]

Thanks for the replies. Great stuff Ken, I have some work to do. I have owned the bike since 12/09/2001. They haven't been looked at since I've owned it....maybe 4 tire changes. I'm a bad bad bad man.

Clean and re-grease every tire change is crazy talk in my book, but not touching them for a dozen years is definitely not the best service interval either.

[Roy Gavin]

http://www.cycleworks.net/index.php?mai ... h=29_41_44

CycleWorks has the shims, but if you order the kit it might be wise to measure your original wedding band and tell them which way you want to go.

[ME 109]

Clean and re-grease every tire change is crazy talk in my book

In most cases you're right Major.
Consider though the GS rider, and those who get phenomenal mileage from their tyres.
I don't do mine every tyre change, but I would every second.
Add the situation of our quirky preload requirements, that could smoke a pair of bearings very quickly.

[Deleted User 62]

http://www.cycleworks.net/index.php?mai ... h=29_41_44

CycleWorks has the shims, but if you order the kit it might be wise to measure your original wedding band and tell them which way you want to go.

They also have a tool for greasing the bearings while still in the wheel.