K100 and K75 front wheel bearing preload

rawdonball · 1 K100 and K75 front wheel bearing preload Sun Mar 20, 2016 3:42 am

rawdonball

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I have finally forced my old 'older' brain to comprehend (I think) what I am actually doing when I tighten the bolt which screws axially into the left hand end of the front wheel mounting shaft.

Went looking on the Forum for confirmation - TWB puts it well in his 'Big Block' blog around post 35

To help get my head around the design concept, I had to remove the wheel from my K100RS and thread the axle through the left hand fork eye from inside to outside. Then I slide spacer, wheel bearing, spacer tube, wheel bearing, and other spacer onto the axle. The distance from end face of axle to end face of last spacer, was what one normally sees to end face of left fork when screwing in the axial bolt with bevel washer on normal front wheel assembly. The more one tightens this axial "spacer clamping" bolt, the closer the two bearing inner races will be to each other (by the amount that the inner tube sleeve is compressed)

When I fit the new wheel bearings to my front wheel I'm going to see if I can detect additional bearing drag after TORQUING the M10 x 20 bolt...

Has anyone noticed a variation

Until I understand this better, this is one bolt I won't be doing up "BY FEEL"

Rick G · 2 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 4:26 am

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You would need to put 150ft/lb before you even stand a chance of compressing that sleeve. You would most likely strip the thread before any compression took place. Ball races like that should not have ANY preload.

rawdonball · 3 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 10:30 am

rawdonball

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What got me thinking about preload and ball bearings was doing another steering knuckle replacement on a '94 Corolla for a Mate. With that, the M24 nut that gets tightened on the threaded section of the drive shaft stub, initially draws the splined stub shaft into engagement with the internally splined hub and the inside and outside 'inner' races into contact with the spacer tube which in this case is integral with the corresponding 'outer' races. Final torquing (+- 150 ft lbs) sets the preload to the balls which results in noticeable drag - not quite as much as is set on a crown wheel in a final drive.

The old style R series steering head bearings were ball type - anyone know whether they were also designed to be preloaded?

Like you Rick - I've generally associated measured preloading with taper roller bearing arrangements. Thinking about it now, I guess the theory is the same for all paired rolling element bearing arrangements . i.e - if you want to carry the load on more than one rolling element then you guarantee the absence of any clearance by applying an axial pre load?

As for compressing the spacer tube between inner races on the K front wheel - I can do it with my puny pen pusher (once upon a time) fingers! It's just hard to measure the minuscule amount of length reduction with the average cheap micrometer....
I'm going to try measuring the distance between the outer edges of the two outer races on my test set up - before and after tightening the axial loading bolt from snug to full torque.

Can anyone come up with an accurate way of measuring the same distance between the two races when they are mounted up against the retaining shoulders in either side of the wheel hub when the wheel is off the bike?

All academic interest I know but what the hell! Those of us not learning a foreign language have got to keep the grey matter active somehow...

Rick G · 4 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 10:54 am

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If you are using angular contact ball races which is what were used in the steering heads of bikes many yeasr ago but they are designed to take the load in a very different way to a conventional ball race like in the front wheel of our Ks
Here are a couple of pics or google "angular contact ball bearings" and check it out
Don't preload a conventional ball race or they will tear them selves to bits very quickly.

K100 and K75 front wheel bearing preload Double10

K100 and K75 front wheel bearing preload Drawin10

rawdonball · 5 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 11:19 pm

rawdonball

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Cheers Rick,

Your first pic is the Corolla set up exactly. I must have had a memory problem again as it is clear that this arrangement is pre loaded by axial compression of the inner races.

I'm keen to establish exactly what the situation is with the design for the k front wheel bearing config in regard to axial clearance or preload - i.e : just how critical is the torque of that axial bolt that we do up to 24 ft lbs (33Nm). I'll set the bearings and spacers up on the axle again (without the wheel) and measure the distance between outer races with axial bolt snugged and again with full torque so at least we know where we stand as to the extent of axial compression. The next thing will be to come up with a way of accurately measuring the distance between the two shoulders which locate the outer races in the wheel bore.

Rick G · 6 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 12:34 am

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What that bolt does is hold the axle into the fork leg and all the components in place then you tighten the 4 bolts on the bottom of the sliders to hold the whole lot in the forks. You should not be able to put any preload on the ball races using that bolt if you do preload them there is something wrong.

K75cster · 7 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 4:33 am

K75cster

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What are you aiming at with the front axle, do you think the ball race should be shimmed to perfection or something like that?

charlie99 · 8 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 7:00 am

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RicK G wrote:What that bolt does is hold the axle into the fork leg and all the components in place then you tighten the 4 bolts on the bottom of the sliders to hold the whole lot in the forks. You should not be able to put any preload on the ball races using that bolt if you do preload them there is something wrong.

agree rick ....wasn't there something about bouncing the front end to settle the forks in the right place (which makes sense to me) .....yes I know about the legs to triple tree bounce as well .

rawdonball · 9 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 10:20 am

rawdonball

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I removed a set of front bearings from the wheel of one of my K bikes just the other day, so held the inner tube spacer in my hand for the first time - realized I didn't fully understand how the set up is designed to work.

My interpretation of what Rick is saying is as follows :- The design of the wheel hub is such that when the two outer races are seated up against their respective locating shoulders, the inner races are in contact with the inner race spacer tube. When the axle end bolt (with the beveled washer) is tightened the length reduction of the inner race spacer tube is less than the combined internal clearances (measured axially) of the two wheel bearings and therefore no pre load is applied to the bearings.

On refection, I think he is probably right in this regard.

He also maintains that no amount of over tightening of the axle end bolt will compress the inner race spacer sleeve to the point at which an axial pre load is applied to the wheel bearings - I think this claim is probably wrong.

So in all likelihood it's no big deal for people who have a feel for these things or for people who regularly use an accurate torque wrench. For a one time pen pusher like me (who likes to think he can figure out when a stated torque is critical and when it's not) it's better if I understand how a thing is designed to function so I can spend the half day looking for my suspect torque wrench when it is sufficiently important. When I'm trying to understand something, I've learned that its best to ask and listen in addition to pondering over theoretical alternatives. I've got quite good at asking but am still pretty shit at listening... (as Rick is discovering no doubt).

To answer K75cster's question, I'm not into shimming for the hell of it!!!!!

Charlie 77 - your reference to 'bouncing' the front forks doesn't (as I see it) affect the way anything is already arranged in terms of position of axle with respect to left fork or position of any spacers or inner bearing races on the axle. It seems to me that these are positioned when the axle end bolt is tightened and that the left fork pinch bolts might as well be tightened at this stage. As TWB put it, bouncing encourages the right fork to 'float' on the large journal end of the axle and find its optimum position relative to the left fork before it is clamped to the axle by tightening the respective pinch bolts.

charlie99 · 10 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 12:55 pm

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yes exactly rawdon ..lets the right leg find its home, whilst the pinch bolts are loose

as for preload I don't think that that exists in this case , it is simply applying a constant of applied pressure to the whole assembly including the inner bearing race at a gap predefined by the spacer tube. spacers either side ...as you describe keep it all tight , an incorrect relative location of the outer bearings in the hub could add additional and unwanted preload for the bearings ....if it was preload you may not be able to turn the wheel as the axel bolt is tightened and the bearings wouldn't last long at all if it did . I believe that the type of bearing used in this application is described as a deep groove type ball bearing ,
preload might be a better description of a bevel type taper roller bearing use and application rather than a plain ball type bearing.

Holister · 11 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 10:05 pm

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I looked into this last year when I replaced my wheel bearings and found no reference to pre-load.
As far as I can see, when tightening the axel you are applying force between the axle collar on the r/h side to the bearing race, thru the inner spacing tube to the l/h bearing race, to then rest against the l/h spacer. All held in place with the bevelled washer and M10 wheel bolt. The only way pre-load could be applied is if the length of the internal spacer could be reduced by applying greater presure. The is no mechanism in that arrangement to allow for this to happen.

In tightening the front axle, I found it was important to get the correct alignment of the forks as they attach to the axle. The very slightest variation in alignment will mean that the front discs will rub in the calipers. Once all was in position with fastenings all slack, I applied and held the front brakes to ensure the disc/wheel was suitably aligned in relation to the forks. I then nipped up the fork bolts very slightly till there was just a little tension from the forks on the axle. I then rotated the axel a ¼ turn 2 or 3 times to make sure the forks were seated on the axel. Tightened the axle to spec and then the l/h fork bolt and lastly the r/h fork bolt. It should be noted that untill the r/h fork bolt is tightened, the r/h fork is floating. The l/h fork is held in place as part of the spacing on the axle but the r/h fork needs to find its own position before it's tightened and has to be done last.
(Note: l/h and r/h are as you are sitting on the bike ie; the wheel bolt and bevel washer are on the l/h side)

Last edited by Kaptain Holister on Mon Mar 21, 2016 11:03 pm; edited 1 time in total

rawdonball · 12 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 11:02 pm

rawdonball

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"There is no mechanism in that arrangement to allow for this to happen"

Hi Kaptain,

Thanks for your thoughts / experience...

You agree with Rick in regard to the inner race spacer tube being incompressible as compared to the axial clearances in the wheel bearings. If I was the calculating sort I would try and verify this by looking up the internal clearance in a bearing catalogue, multiplying this by two and comparing it with the calculated elastic deformation of the tube using its length, cross-sectional area, young's modulus and the compressive force generated by the M10 bolt torqued to spec. Being lazy, I prefer to do it by practical measurement but i'll use extra spacers on the shaft instead of the actual bearings as this will make it easier for me to use my outside micrometer. Plus I won't be messed around by the internal bearing clearance when measuring between outside edges of the bearing outer races as I originally envisaged.

Holister · 13 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 11:50 pm

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Rawdon, just my opinion based on my uneducated and visual assessment of the inner spacer tube, but I feel its not substantial enough or well enough engineered to maintain any forces that would be great enough to "deform" it. I may be wrong but from memory I think it is just a piece of seam welded pipe. I think if BMW had intended the bearings to be pre-loaded then they would have designed something more substantial that would take that force and hold it within fine tolerances. I'm no expert in this matter. Just my thoughts mate.

It'll be interesting to see what you come up with and I'm happy to be proven "out of my depth" K100 and K75 front wheel bearing preload 2Q==

Point-Seven-five · 14 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 2:12 am

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Assuming the width of the inner race of the bearings is the same as the outer race, the critical dimension is the length of the pipe/spacer. It should be as close as possible to the distance between the shoulders in the wheel hub that the outer bearing races rest against. The rest of the parts are not as critical as long as the pipe can prevent side loading of the bearings by the rest of the axle components. At 24 ftlb compression on the pipe is negligible, if not essentially zero.

The torque on the screw at the end of the axle is just enough to take up the slack in the stack while putting minimal compression on it. Clamping the large end of the axle in the bottom of the right leg allows for a wide tolerance in the distance between the fork legs.

K75cster · 15 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 2:18 am

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I would very much like to know how you get on Rawdonball, as it is interesting to know if the operation of our front forks over the last 30 years has caused the inner and outer race surfaces to not be at optimal. Same goes for the forks, when they are seated or fully compressed that is the best place to see if the spacer is the correct spacer for that fork, I remember many boy racers going to great lengths to improve the performance of their forks years ago, certainly our forks would be or could be improved by attention to detail and it is all the little bits that add up to an exception ride No?

rawdonball · 16 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 3:42 am

rawdonball

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Got to fill out personal details for a job application - shit load of paper work for one week of night shift. At least it might be an opportunity to get back to East Coast (Qld) and pick up mirrors from Rick G... (plus fairing bits from the Kaptain)

So 0.75 - aren't you going to commit as regards how the 'minimal' compression of the spacer sleeve might compare with bearing internal clearances (axial)???

Kaptain - I take your point, the sleeve does look a bit piss willy for something that has a critical job to do...
But - if it has anything to do at all, it is either to resist the minimal compressive force (which it can only do by deforming albeit only slightly) or it can control the extent of pre load by deforming slightly more than the axial internal clearance of the bearings

rawdonball · 17 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:23 am

rawdonball

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K100 and K75 front wheel bearing preload Photo-10

You can see this measurement was a bit rough and ready!
I'm using two of the narrow spacers together in the one end in order to be able to get access as best I can for now, with the micrometer. I found reasonable repeatability despite the flange on the spacer being a little out of true.
At this stage it looks like the compression in the tube spacer, two inner races and one narrow spacer, is about 0.1mm (4 thou)

rawdonball · 18 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:28 am

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K100 and K75 front wheel bearing preload Photo-11

Reading with axial bolt snugged

rawdonball · 19 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:43 am

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K100 and K75 front wheel bearing preload Photo-12

34 Nm on my now suspect 30 year old Britool

K100 and K75 front wheel bearing preload Photo-13

Opposite end of micrometer on single wide spacer flange

rawdonball · 20 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:47 am

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K100 and K75 front wheel bearing preload Photo-14

This reading with the axial bolt (a slightly longer one - bit tight in the threads) torqued to 34 Nm

Sorry to drag you guys through this exercise of me giving myself practice at posting photos

Point-Seven-five · 21 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 9:31 pm

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I am puzzled. What do you expect in the way of precision measurements by putting the micrometer on the dirty dust cover of the spacer?

If I was doing a quality audit of the front end parts I would first spotlessly clean all the parts and then measure from the end of the axle where the beveled washer is installed to the shoulder on the other end.

Then, I would measure individually each of the parts stacked on the axle including the bottom of the fork leg. The bearing inner races, spacers, and the spacer between the bearings. The sum of these measurements should be exactly the same or within .001-.002" of the first measurement. I would not expect them to be much greater than the first measurement as that would result in undesirable side loading on the bearings.

Another measurement that I would make is the distance between the shoulders in the wheel hub that support the outer races of the bearings. That dimension should be the same as the length of the spacer pipe that goes between the bearings. Differences here would result in static and dynamic side loading of the wheel bearings.

If, and only if, the stack measurement was greater than the length to the axle shoulder I would assemble the axle in the forks with the pinch bolts loose. I would put only enough torque on the cap screw to take out the spaces between all the parts. Then I would tighten the pinch bolts on the bottom of the left leg. Torque the cap screw and then work the forks several times and tighten the pinch bolts on the bottom of the right leg.

If the goal is to have zero wheel play on the axle with minimal side loading on the wheel bearings these are the only measurements that have any meaningful relationship to the static side loading of the wheel bearings in the assembled front end.

As far as the torque on the cap screw. I would guess that is what is required to insure that the screw never loosens. After all, it is installed in an unsprung location subject to all the shock and vibration coming from wheel contact with the road surface.

Personally, barring a 60's or 70's vintage British or Spanish machine, there are things I am willing to trust to the machine's builder, and unless I was going through wheel bearings more often than rear tires I wouldn't give all this stuff even a second thought on a BMW.

rawdonball · 22 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 10:17 pm

rawdonball

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The chastisement is accepted (as gracefully as possible!!!)

The primary objective of this part of the exercise was to induce others who might not normally give it a second thought, to maybe give it a go. So far I've enjoyed it and it's prompted me to read up on the relation ship between radial and axial clearances in deep groove ball bearings and why pre load is important. Not everyone's cup of tea but fascinating to me.

Feedback much appreciated in principle - I'll read it again when my slow brain can get to concentrate. Got to secure the four nights of shift work first!

Point-Seven-five · 23 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 10:43 pm

Point-Seven-five

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Yeah, it's fun as a mental exercise, but the beauty of these machines is that we shouldn't have to worry about things like that and just enjoy the final product. As long as we follow the maintenance procedures with diligence these beasts seem to be really easy to live with.

No harm meant, mate. Just a bit of friendly ragging. You brought up a topic that few, if any, of us would otherwise ever think of.

rawdonball · 24 Re: K100 and K75 front wheel bearing preload Wed Mar 23, 2016 10:26 am

rawdonball

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Point-Seven-five wrote:I am puzzled. What do you expect in the way of precision measurements by putting the micrometer on the dirty dust cover of the spacer? I am lazy! I was after a comparison of the distance between the two spacer flanges in the two different conditions. a) with the axle end bolt just snugged and b) with the axle end bolt torqued to spec. I didn't want to bother with cleaning until I could see that there was a significant difference between a( and b). When I discovered the difference was significant I also discovered that the readings varied very little when I repeated the exercise - hence I never got to do the cleaning

If I was doing a quality audit of the front end parts I would first spotlessly clean all the parts and then measure from the end of the axle where the beveled washer is installed to the shoulder on the other end. I'm not doing a quality audit - I trust the quality unless I can see evidence of abuse

Then, I would measure individually each of the parts stacked on the axle including the bottom of the fork leg. The bearing inner races, spacers, and the spacer between the bearings. The sum of these measurements should be exactly the same or within .001-.002" of the first measurement. I would not expect them to be much greater than the first measurement as that would result in undesirable side loading on the bearings. The two measurements you describe, differ by about 5mm at least..

Another measurement that I would make is the distance between the shoulders in the wheel hub that support the outer races of the bearings. That dimension should be the same as the length of the spacer pipe that goes between the bearings. Differences here would result in static and dynamic side loading of the wheel bearings. I haven't thought of an accurate way to measure the distance between the outer race locating shoulders. I think we can safely assume that this dimension in the 'as designed' condition, will be equal to the spacer tube length +- 2 x bearing internal axial clearance (when installed)

If, and only if, the stack measurement was greater than the length to the axle shoulder I would assemble the axle in the forks with the pinch bolts loose. I would put only enough torque on the cap screw to take out the spaces between all the parts. Then I would tighten the pinch bolts on the bottom of the left leg. Torque the cap screw and then work the forks several times and tighten the pinch bolts on the bottom of the right leg. Interesting

If the goal is to have zero wheel play on the axle with minimal side loading on the wheel bearings these are the only measurements that have any meaningful relationship to the static side loading of the wheel bearings in the assembled front end. Agreed (If that is the design objective)

As far as the torque on the cap screw. I would guess that is what is required to insure that the screw never loosens. After all, it is installed in an unsprung location subject to all the shock and vibration coming from wheel contact with the road surface. It's a reasonable guess

Personally, barring a 60's or 70's vintage British or Spanish machine, there are things I am willing to trust to the machine's builder, and unless I was going through wheel bearings more often than rear tires I wouldn't give all this stuff even a second thought on a BMW. I trust the design and the production methods. I like to understand the design where possible - e.g to minimize the chances of me resorting to tightening by feel, in a case where a specific torque is critical to meet the design objective

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1 K100 and K75 front wheel bearing preload Sun Mar 20, 2016 3:42 am

rawdonball

2 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 4:26 am

Rick G

3 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 10:30 am

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4 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 10:54 am

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5 Re: K100 and K75 front wheel bearing preload Sun Mar 20, 2016 11:19 pm

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6 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 12:34 am

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7 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 4:33 am

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8 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 7:00 am

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9 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 10:20 am

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10 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 12:55 pm

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11 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 10:05 pm

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12 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 11:02 pm

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13 Re: K100 and K75 front wheel bearing preload Mon Mar 21, 2016 11:50 pm

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14 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 2:12 am

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15 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 2:18 am

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16 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 3:42 am

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17 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:23 am

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18 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:28 am

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19 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:43 am

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20 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 6:47 am

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21 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 9:31 pm

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22 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 10:17 pm

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23 Re: K100 and K75 front wheel bearing preload Tue Mar 22, 2016 10:43 pm

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24 Re: K100 and K75 front wheel bearing preload Wed Mar 23, 2016 10:26 am

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25 Re: K100 and K75 front wheel bearing preload

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