Wheel bearing pre-load - '83 100RT

[H. Huester]

Bottom line up front: Is it really that important to adjust pre-load on the wheel bearings, and if so, what is an easy way to do that?

A bit of a disclaimer. I know all about over-thinking, over-engineering, and over-talking... most any issue. I'm comfortable with that... I'm German... it is simply my (and my fellow countrymen's) cross to bear - end of conversation! Having said that...

I'm installing bearings (and races) into the snowflake wheels of an '83 100RT - the front ones are new, the rear ones are the ones that came out. Have done this lots of times in my cars - it's a no-brainer. Of course, those were not BMW motorcycles that I was working on, but Triumph and MG sports cars. Now that I'm reading the rest of the procedure... I'm encountering the concept of "bearing pre-load" and the purpose of the spacer and "wedding band" inside the hub (between the bearings). Having read two manuals over and over (they don't really tell you how), searching multiple websites (that tell you how to extract the ore to make the mold, that makes the tool...), and chatting with the BMW mechanics (who want $97 per wheel to do it themselves), I got to ask myself... WTF - does it really have to be SO difficult?

I've looked a numerous sites attempting to explain the concept, and walk you through the process. Just by reading their procedure, I quickly pick up on the detail-oriented nature of these well-meaning folks. If they are not already German by birth, their obsessiveness (bordering at times on the side of lunacy), certainly qualifies them for honorary membership.

I've changed bearings on numerous cars over the years... and quite frankly, I NEVER expected them to last 2+ million miles (like is advertised IF you properly adjust the pre-load on the BMW bearings). I can also "what if" with the best of them (what if the bearing seizes in a fast left-hand sweeper with a group of drunk skinny-dippers walking in the oncoming lane...)... the truth is, I have NEVER had a bearing fail on me - PERIOD.

So, help me out here - I don't get it! How important is pre-load? How does one do it without spending 42 hours, six special tools, or $200 to do it? What happens if one simply leaves out the spacer and wedding band and torques down the spindle nut like you would on most EVERY OTHER vehicle on the planet?

Thanks in advance, for all your help!!!
Heinz

OBTW - a couple more things: My apologies to all those well-meaning, detailed-oriented, obsessive owners of BMW motorcycle-related websites - I appreciate what you are doing to further the knowledge of those (like me) that are lees-inclined.

Also, if your answer involves the use of mathematics, a slide rule, or anything close to a computer... it's not what I'm looking for.

Love you guys - I learn a ton on this site!!!!!!!!

[Rob Farmer]

This has come up in a previous thread http://www.advrider.com/forums/showt...=wheel+bearing

It's not difficult at all once you work though it. The official BMW tool isn't available but a small torque wrench does the trick. I bought a couple of very cheap presettable screwdrivers on Ebay and a calibrated gauge for setting them up. It probably cost the same as having a dealer do one bearing to get set up but now it's very cheap and easy.

The only real pain in the arse is having to have a selection of the "Wedding bands". You get an awful lot of them for $97 though.

If the bearings are too tight the grease squibs out and the bearings fail in a very short period of time so it's worth getting right.

[StephenB]

There is plenty of information out there.Take this for example as the long answer: http://w6rec.com/duane/bmw/wheel_bearing/index.htm
Need more info, search google for BMW bearing preload and you'll find plenty to read.

The short answer is: all single row tapered roller bearings (correct technical name for that type of bearing) need preload to work properly, not just no play -> preload. It is used in swingarm, steering head and wheel bearings and needs pre-load in all three cases, including the steering head! Read about that in every text book.
Not getting it right can lead to serious problems such as speed wobbles ... both ways, too loose or too tight in swingarm,/steering and/or wheels. Get it right! Don't take it lightly. No need for special BMW tools, but you need a variety of "wedding bands" that are not very costly and some time plus some HomeDepot type special tools.

[StephenB]

There is a similar thread on Boxerworks as we speak: http://boxerworks.com/phorum/read.ph...49382&t=249382

[One Less Harley]

I just did the bearings on my G/S which had tapered roller bearings and noticed the wedding band spacer #10 (6.3-7.7mm) was to thick allowing to little preload on the bearings, so what I did was measure the existing band and order some thinner ones.

Remove the bearing seals and put your wheel back on the bike and and push and pull it at the same time at the 3 and 9 oclock positions to judge the amount of play. If there is play then the spacer will need to be thinner if no play and wheel spins with resistance or grittiness the spacer will need to be thicker. This is assuming that the bearings are good. Measure the spacer then order a few smaller or bigger ones. Slowly work your way up or down in size. I prefer to work from the wheels being loose with a little play and going till the play is just gone.
No measuring preload this way, I'm sure others may prefer actually measuring the preload, but this is the way I've done cars and bicycles for years.

[Rob Farmer]

So nobody is interested in the correct way of doing it then? Very strange.

[kixtand]

Originally Posted by Rob Farmer

So nobody is interested in the correct way of doing it then? Very strange.

I beg to differ. Please elaborate on the correct method .

kix

[Andy-Gadget]

If you go into the BMW agent to buy different shims (wedding bands), take a micrometer or vernier caliper with you, the size from the part number isn't always the actual size

I solved this by making my own
I was working as a tool maker at the time, '90 to '94, and am still running on the shims I made then.
They are better than the BMW ones to, in 0.025 mm jumps, not the BMW 0.05, and make of hardened silver steel.
But I was lucky to be able to be able to do this.

I have always just taken the free play out, not what the book says to do, but I do mine more often than most people.

BTW the historical reason for the tapered rollers being fitted is thanks to side cars, shallow groove ball bearings (normal ball bearings) don't like too much side load, but tapered roller bearings are designed to take just such a load.
Even if they were angular contact balls, we would still need to shim them

Originally Posted by Rob Farmer

This has come up in a previous thread http://www.advrider.com/forums/showt...=wheel+bearing

It's not difficult at all once you work though it. The official BMW tool isn't available but a small torque wrench does the trick. I bought a couple of very cheap presettable screwdrivers on Ebay and a calibrated gauge for setting them up. It probably cost the same as having a dealer do one bearing to get set up but now it's very cheap and easy.

The only real pain in the arse is having to have a selection of the "Wedding bands". You get an awful lot of them for $97 though.

If the bearings are too tight the grease squibs out and the bearings fail in a very short period of time so it's worth getting right.

[H. Huester]

Originally Posted by Rob Farmer

So nobody is interested in the correct way of doing it then? Very strange.

Actually, I'd love to know... preferably, in a way that makes sense though.

[H. Huester]

Originally Posted by Andy-Gadget

BTW the historical reason for the tapered rollers being fitted is thanks to side cars, shallow groove ball bearings (normal ball bearings) don't like too much side load, but tapered roller bearings are designed to take just such a load. Even if they were angular contact balls, we would still need to shim them

Do they make sealed bearings that replace the whole package in there now?

[RandyB]

Timely thread as I am rebuilding my 84.

Is is possible to pull everything out and repack the bearings then replace the seals without messing up the preload?

Or does disassembly mess it up?

[One Less Harley]

disassembly won't mess things up. but if your bearings are worn....

[Boon Booni]

Originally Posted by Rob Farmer

So nobody is interested in the correct way of doing it then? Very strange.

I see your "screwdriver torque wrenches" and raise you the diameter of your axle, a piece of string, a spring loaded weight gauge, and a few calculations involving torque.

Originally Posted by RandyB

Timely thread as I am rebuilding my 84.

Is is possible to pull everything out and repack the bearings then replace the seals without messing up the preload?

Or does disassembly mess it up?

Absolutely, but I'd try and keep the two bearings separate. Make sure the left goes back in the left side and the right goes back in the right side.

[Wirespokes]

Back in the old days (I'm probably dating myself here) the old trucks and cars I drove required front wheel bearing servicing. That meant cleaning out the old grease, repacking and then readjusting the bearing tension. There was a large, loose fitting washer under the nut that held everything together, and when the tension was correct, that washer could be forced to slide when pried on with a screwdriver.

That was how you did it. Rocket science!

Our beemer bearings are the exact same bearings, but don't have nuts with washers to secure them. But they need some pressure on them to operate properly.

With our wheels there are two forces to consider - the force holding the outer races (of the two bearings) apart, and the force compressing the inner races together.

The outer races are held apart by the hub - not much you can do about that. It is what it is.

The inner races are forced together by the torque on the axle (don't overtorque the axle nut!), which compresses the inner races against those inner spacer pieces.

The idea is that those inner spacer pieces allow some tension on the bearings so they don't run loose. If you've ever adjusted wheel bearings you'll know what it feels like when it's right. But just like using a feeler gauge adjusting valves, the first time may be awkward, but once you've got the 'feel' it's easy.

[StephenB]

Originally Posted by Wirespokes

The inner races are forced together by the torque on the axle (don't overtorque the axle nut!), which compresses the inner races against those inner spacer pieces.

The hub fixes the location of the two races (you were correct there) together with a large outer spacer. The preload and therefore the position of the rollers (centered) is determined by a combination of (from the outside to the inside) two compression rings, the two bearing hubs (with rollers), an inner spacer and correct size wedding band The axle torque does not matter in this equation. It squeezes the a.m. parts and that's it. It can not bee too tight (unless you apply such a torque as to deform the steel !). You had it nearly right there.



Parts are shown as they are assembled. The assembly is called a stack because if you assemble all the parts and line them up and cool them down, you can actually drive this stack into the heated hub. I think that is true for all rear hubs.

The outer races are held apart by the hub - ...

That is incorrect, the outer races on the rear hub are held apart by an outer spacer. The hub holds the complete stack by means of holding the two outer races in a slight pressfit. Your statement is true for the front wheel where the outer races are driven into the hub until they bottom out. There is an outer space apparent in the front hub but I don't think it is being used.



Sorry for the large picture (both representing rear (top) and front (bottom) bearing stack of a /5.

Front and rear drum-type hubs were actually the same. The only thing that did change was removing the reduction sleeve(allowing the 14mm axle to be usd on /5s) which lead to the intruduction of the 17mm front axle on drum-type front hubs.

I am not sure whether the information is true for later front wheels, but I think you get the picture about bearing preload in general.

I hope it helps.