Bearing Stack Question - 1976 BMW R75/6

[b25bsaboy]

Good afternoon,

I always suspected that when I rebuilt my R75/6 wheels I really didn't understand the methodology of how and why. With working full time and travelling, one has to slow down and think, thus I am back to the front and rear wheel bearings install. Researched as much as I can and YouTube was helpful in helping me understand the process. I have several questions now that I have removed the bearing assembly I have failed to find and answer, thus I turn to the MOA Airhead section:

1. When you assemble everything on to the wheel spindle shaft, I have seen several examples of the nut being tightened hand tight or to reported torque value of 35 ft/lbs before you install back into the hub. Any thoughts on this? I understand the freezing the assembled unit and not to pack the bearings till after they are installed and to heat the hub up till 200 degrees F.

2. The second issue that I have when everything is assembled, torqued to 30 ft/lbs, I find the outer centre outer bearing spacer that is butted up to the back of the bearing cup is not snug. Thus I can put a .001 feeler gauge in between the two mating parts. Is this normal? I had a nice 16 second movie that I have tried to up load which illustrates what I am seeing. Does the wedding band need to be made thinner or leave alone?

Appreciate everyone's input.

 

[20774]

Matt Parkhouse has a write up in February's ON about just this subject. Also, Duane Ausherman has a webpage on this:

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

RE: 1) I don't think the torque of the stack before installation is critical. It just needs to be tight enough to keep everything together as it is inserted into the hub. The preload is done before any grease is added to the bearings. Once you've established the proper preload, then you should grease the bearings and freeze the bearing stack. After the hub is heated, drop in the stack. Matt discusses this.

RE: 2) Matt and Duane discuss how to measure the preload. It sounds like you might not have the right preload. If there is a gap or the middle spacer is easily moved, then the wedding band must be changed to a smaller size. Either you fit the new spacer, or you take the old one out and use a series of sanding motions (basically figure-8 patterns) to thin the spacer. You should be measuring the spacer as you do this.

 

[b25bsaboy]

Matt Parkhouse has a write up in February's ON about just this subject. Also, Duane Ausherman has a webpage on this:

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

RE: 1) I don't think the torque of the stack before installation is critical. It just needs to be tight enough to keep everything together as it is inserted into the hub. The preload is done before any grease is added to the bearings. Once you've established the proper preload, then you should grease the bearings and freeze the bearing stack. After the hub is heated, drop in the stack. Matt discusses this.

RE: 2) Matt and Duane discuss how to measure the preload. It sounds like you might not have the right preload. If there is a gap or the middle spacer is easily moved, then the wedding band must be changed to a smaller size. Either you fit the new spacer, or you take the old one out and use a series of sanding motions (basically figure-8 patterns) to thin the spacer. You should be measuring the spacer as you do this.

Morning Kurt,

First off Thank you for the expanded explanation. I went back and reread this month's article MOA by Matt and it does explain the preload issue. I then went to Duane Ausherman's web sit and found the answer to my question. This is a learning experiance for a guy that is pushing 70 and I am amazed to the amount of information out there and one just has to absorbe thus sorting it out the best course to take.

 

[kjmcd13]

Bearings

Found this, its not too bad.......http://steves-workshop.co.uk/vehicles/bmw/wheelbearing/wheelbearingindex.htm

 

[20774]

Nice link...here's another:

http://advrider.com/index.php?threads/installed-new-front-wheel-bearing-on-my-6.388220/

 

[30064]

Good afternoon,

I always suspected that when I rebuilt my R75/6 wheels I really didn't understand the methodology of how and why. With working full time and travelling, one has to slow down and think, thus I am back to the front and rear wheel bearings install. Researched as much as I can and YouTube was helpful in helping me understand the process. I have several questions now that I have removed the bearing assembly I have failed to find and answer, thus I turn to the MOA Airhead section:

1. When you assemble everything on to the wheel spindle shaft, I have seen several examples of the nut being tightened hand tight or to reported torque value of 35 ft/lbs before you install back into the hub. Any thoughts on this? I understand the freezing the assembled unit and not to pack the bearings till after they are installed and to heat the hub up till 200 degrees F.

2. The second issue that I have when everything is assembled, torqued to 30 ft/lbs, I find the outer centre outer bearing spacer that is butted up to the back of the bearing cup is not snug. Thus I can put a .001 feeler gauge in between the two mating parts. Is this normal? I had a nice 16 second movie that I have tried to up load which illustrates what I am seeing. Does the wedding band need to be made thinner or leave alone?

Appreciate everyone's input.

Rick,

First of all you need to realize there's going to be a lot of opinions regarding preload and procedure. I'm going to share my personal opinions and procedure as a direct result of my personal study, and experience.

What you're showing in the picture is my definition of static preload. First lets talk about your take-up collar ... the spacer with the blue tape on it. This is a very important piece of equipment when performing preload and axial tension to the bearing stack. The take-up collar ends should be precisely machined on a lathe so the ends are as close to perpendicular to the centerline bore as possible. If not you will experience radial stepping when the stack is torqued. Try to acquire a spacer with smooth perpendicular ends if you don't have access to a machinist. Take the stack when assembled as in your picture grasping both ends of the axle and roll it on a clean flat surface several times. This will align things and "basically" center the roller bearings and outer spacer. The rule of thumb for the static setting is with the stack assembled with clean and lightly oiled bearings (no grease) and a torque of ±28-30 ft-lb on the axle nut the outer spacer should slide back and forth with your thumbs with moderate resistance. This is not an analytical measurement but should get you close. If the outer spacer moves too freely you need to decrease the width of your wedding band. If it moves with too much effort or doesn't move at all you need a wider wedding band. It's preferred you don't hand mill the wedding bands. Even if you're very careful using a figure-8 motion on a flat surface it's very unlikely you will be able to decrease the wedding band width equally and perfectly flat. You can obtain different wedding band widths in increments of 0.05mm through many suppliers.

http://www.realoem.com/bmw/enUS/showparts?id=0304-EUR-06-1977-2474-BMW-R_100_7&diagId=36_0157.

I personally no longer use the 0.05mm stamped shims that are popular - just my personal opinion. I like to find the correct width wedding band in it's original form.

NEVER exceed 35 ft-lbs of torque on either of your axle nuts. Correct preload should be had at 28-30.

This should get you close. The final check should be with the bearing stack installed in the wheel hub, clean lightly oiled bearings, axle torque to 28-30 ft-lb. Many things can change with the stack outside the hub vs. inside the hub. I would recommend you visiting Snowbum's web site regarding wheel bearings. It's lengthy but he's gone to great effort taking you through the steps and operation of the tapered wheel bearing operation and proper preload.

I would also recommend if you have the inclination, time and diligence to obtain the necessary tools to do the string pull test that measures inch-oz's of rolling resistance for preload. It's all on Bum's site. This may seem like a lot of work and overly anal, but it will give you a very good idea of the correct "feel" of proper preload by actual analytical values so you can have that knowledge the next time you perform the job. Then you can speed up the process once you develop the correct feel.

I hope this answers some of your questions and doesn't muddy the water for you any further. Just my personal opinion - and recommendation. Your mileage and procedure may vary along with many others here on the forum.

-Mike V. / San Diego

 

[b25bsaboy]

Rick,

First of all you need to realize there's going to be a lot of opinions regarding preload and procedure. I'm going to share my personal opinions and procedure as a direct result of my personal study, and experience.

What you're showing in the picture is my definition of static preload. First lets talk about your take-up collar ... the spacer with the blue tape on it. This is a very important piece of equipment when performing preload and axial tension to the bearing stack. The take-up collar ends should be precisely machined on a lathe so the ends are as close to perpendicular to the centerline bore as possible. If not you will experience radial stepping when the stack is torqued. Try to acquire a spacer with smooth perpendicular ends if you don't have access to a machinist. Take the stack when assembled as in your picture grasping both ends of the axle and roll it on a clean flat surface several times. This will align things and "basically" center the roller bearings and outer spacer. The rule of thumb for the static setting is with the stack assembled with clean and lightly oiled bearings (no grease) and a torque of ±28-30 ft-lb on the axle nut the outer spacer should slide back and forth with your thumbs with moderate resistance. This is not an analytical measurement but should get you close. If the outer spacer moves too freely you need to decrease the width of your wedding band. If it moves with too much effort or doesn't move at all you need a wider wedding band. It's preferred you don't hand mill the wedding bands. Even if you're very careful using a figure-8 motion on a flat surface it's very unlikely you will be able to decrease the wedding band width equally and perfectly flat. You can obtain different wedding band widths in increments of 0.05mm through many suppliers.

http://www.realoem.com/bmw/enUS/showparts?id=0304-EUR-06-1977-2474-BMW-R_100_7&diagId=36_0157.

I personally no longer use the 0.05mm stamped shims that are popular - just my personal opinion. I like to find the correct width wedding band in it's original form.

NEVER exceed 35 ft-lbs of torque on either of your axle nuts. Correct preload should be had at 28-30.

This should get you close. The final check should be with the bearing stack installed in the wheel hub, clean lightly oiled bearings, axle torque to 28-30 ft-lb. Many things can change with the stack outside the hub vs. inside the hub. I would recommend you visiting Snowbum's web site regarding wheel bearings. It's lengthy but he's gone to great effort taking you through the steps and operation of the tapered wheel bearing operation and proper preload.

I would also recommend if you have the inclination, time and diligence to obtain the necessary tools to do the string pull test that measures inch-oz's of rolling resistance for preload. It's all on Bum's site. This may seem like a lot of work and overly anal, but it will give you a very good idea of the correct "feel" of proper preload by actual analytical values so you can have that knowledge the next time you perform the job. Then you can speed up the process once you develop the correct feel.

I hope this answers some of your questions and doesn't muddy the water for you any further. Just my personal opinion - and recommendation. Your mileage and procedure may vary along with many others here on the forum.

-Mike V. / San Diego

Mike,

Thank you for the in depth insight to my question.

As a newbie with Airheads there is a lot I don't know, want to know and need to know, as I have been messing around for a lot of years with British bikes and came over to the BMW side, with which I am glad I did.

To recap what I have done thus far:

I found that the outer spacer was somewhat lose and I have a piece of glass with 240 grit sand paper and did a figure 8 to take off some some excess thickness. The original thickness was .278". After I was finished the thickness is now less .004". The outer spacer after torque it assembled at 23 ft./lbs. was snug and with both thumbs I was able to click out of alignment. I assembled it twice to make sure that I wasn't being mislead. Greased the bearings, put into the freezer for 4 hours, heated the hub to about 175 degrees F and the assembly popped into place. There is without a doubt a simple science to this providing you know what you are doing.

I agree there is a lot of information out there and Snow Bums & Duane Ausherman's articles are OK, if you have the time to sit and digest what he is saying. I only wished there where pictures attached to what he is talking about as this would have helped but weren't included. I went into my library and pulled out the BMW R60/6, 75/6, 90/6 and 90S Repair Manual about the procedure and it too is somewhat lacking, but it does have the pictures showing what they are talking about.

I appreciate your insight and knowledge as with the rest of the contributors on this site.

 

[20774]

Glad your job went well! Personally, I don't work well with heat/fire!!

Duane used to sell very thin shims which could be used to adjust the preload on the bearings. The idea would be that you pick a wedding band spacer that results in too much preload. Then the appropriate sized shim could be added...from the outside without removing the stack...to bring the preload back into the proper range.

Duane talks about the "shake the wheel" test. I think it provides a pretty good indication of preload. The idea seems to be that you should feel some "slop" in the bearing stack at lower torque values...you grab the wheel at say 9 and 3 o'clock and try and move the wheel around the axle. That "slop" should just disappear as you approach that final torque value. The bearings are quite hardy...they will tolerate a modest amount of preload, but if there is no preload, the bearings will probably destruct in very short time.

 

[b25bsaboy]

Glad your job went well! Personally, I don't work well with heat/fire!!

Duane used to sell very thin shims which could be used to adjust the preload on the bearings. The idea would be that you pick a wedding band spacer that results in too much preload. Then the appropriate sized shim could be added...from the outside without removing the stack...to bring the preload back into the proper range.

Duane talks about the "shake the wheel" test. I think it provides a pretty good indication of preload. The idea seems to be that you should feel some "slop" in the bearing stack at lower torque values...you grab the wheel at say 9 and 3 o'clock and try and move the wheel around the axle. That "slop" should just disappear as you approach that final torque value. The bearings are quite hardy...they will tolerate a modest amount of preload, but if there is no preload, the bearings will probably destruct in very short time.

Thank you Kurt and to the others for their input!