Front wheel bearing spacer question

NicD

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Have removed bearings to replace. Spacer seems marginally longer (about 1+mm) than the space between the two bearing seats. I assume that when I replace bearings the spacer will be tight against the inner races. As the spacer is used on lots of BMWs there is clearly a gap in my understanding - why design it this way as will side load bearings surely? Or have I mis-measured?
 
My first thoughts are as there is no clamping force on the outer race of the bearings it should be fine, the inner race is clamped onto the middle spacer as the axle is tightened, if it was an exact fit the same size as the wheel and the outer race was tight on the wheel, side load could be put onto the bearings.



I may be talking bollox but it sounds right in my head
 
Ideally the spacer should be exactly the same length as the space between the bearing seats. But a short spacer would lead to rapid bearing failure so they are usually made slightly longer. It's best to avoid knocking the bearings in too hard against their seats as they will need to be pushed apart when the spindle is tightened.
 
Will be interesting to see on reassembly. I suspect the bearings need to be seated fully, and looks like the spacer and inner races will turn together - certainly the feedback I had asking around today. I also would have imagined that the spacer would be exactly the length of the gap but, either that is wrong or my measuring is wrong!
 
If the spacer is the original one that came out, and assuming the new bearings are identical to the old ones, it should go back together. Either you haven't seated the new bearings fully or you have something like dirt or a burr somewhere.
 
I think the spacer is a dead match to the space face to face of the inner races. Sounds like something is wrong.
 
Would be good to hear from someone who knows the answer. Easy to theorize and go the wrong way

Measurement of spacer length is longer than void between bearing seats. I measured it because end of spacer appeared proud of bearing seat when I removed first bearing

Have reassembled now. Spacer sits tight between both inner races. As you seat the second bearing you need to check spacer alignment, and last two taps the spacer goes from having small free play to being tight to both inner races.

In case anyone still wondering, there were no burrs or damage to any of the relevant parts. If anyone knows why it's engineered like that I'd be interested to know
 
That sounds no different to just about every motorcycle wheel I’ve had apart, the front axle spacer needs to be a proper fit between the inner races to support and prevent side loading.


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Yeah it may be peferctly normal. Never noticed before. As I wrote above, likely a gap in my understanding. I posted the question to try to learn something
 
Put the first bearing on side where seat is shallower, than spacer and the second bearing just to gently touch spacer, forget seat on that side of the hub.
 
What is the reason you say that? I'm not saying it's right or wrong - I do need a good reason though not to seat a bearing fully, preferably an instruciton in the BMW manual or similar
 
1 mm longer spacer is reason, bearings may not have any preload. The seals must be aligned with the outer edge of the hub, measure everything, and it will be so, see BMW Reprom. The left bearing goes first:
 
For seals to fit flush the bearings have to be fully seated.

Am getting a copy of bmw workshop manual to see
 
Seems like they want you to use a draw bolt to pull the right bearing in snug against the spacer and not bash it fully home.
2018_10_02_2.png
 
Thanks for posting that. Very useful.

The only thing is that the manual doesn't make clear the answer to the question I am asking.

The manual states: "Pull in bearing until seated against spacing bushing." The wording for other side: "Pull in bearing until seated."

In both cases the instruction is to 'seat' the bearing.

In my experience, which is far less than many on here, seating a bearing does not mean 'just touching'. It means full contact - the sound and feel of a seated bearing is different from one that is 'just touching'.

Hence when I see the same 'seated' instruciton for both bearings, my interpretation would be that the bearing needs to be tight to the spacer, not just touching it, or not only partially seated.

Do others disagree? Would be interesting to hear from a BMW tech.
 
I am independent BMW mechanic and also GS owner, forums serve for advice. BMW is very specific and not completed very often, must have prior knowledge. It is pretty clear, " pull ,left, bearing until seated, pull,right, bearing until seated against spacer".
 
Been watching this thread and thinking it's all a bit complicated.
Me, if i was doing the job i would seat one bearing install the spacer tap the other bearing
in ensuring the spacer was something like cenral then put the wheel in place, spindle through,
tighten the spindle in and let it complete the job.
too simple? perhaps but, i like the KISS way of doing things.
 
Thanks Tony, I read that comment and I did it differently for two reasons. The axle would load the inner race, not the outer race, and that could mean there is small movement (or forces) between the races. Also, if the two inner races and spacer are supposed to move as one - which is what I suspect the answer is - then that would not happen if there was a small gap between the parts.

Perhaps this is overly complicated. Nonetheless I don't like to do things without understanding them, and on this issue I posted because I didn't understand
 
The important part is ,washer A,. It is sharing the load evenly between the outer and inner bearing tracks. Once the bearing is pulled into contact with the spacer there will be no side loading forces.
 
Is washer A not part of the BMW draw tool assembly to seat the bearings?
 


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