R100/7 front axle specs?

Discussion in 'Airheads' started by Twin headlight Ernie, Jan 12, 2013.

  1. Twin headlight Ernie

    Twin headlight Ernie bar napkin engineering

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    I'm working on a new to me 1978 R100/7. I just mounted up a fresh front tire. What's the torque and procedure for the front axle? This is the first bike I've had that used tapered roller bearings. I figured someone here could walk me through it.

    Thanks.
    2HE
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  2. supershaft

    supershaft because I can

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    If your bearings are adjusted correctly your axle nut torque will not effect your bearing adjustment. The axle nut is not a bearing adjuster nut. It is an lock nut for the axle. If your bearings are too tight with the axle nut torqued to spec (32ftlb??), your bearing preload needs adjusting. After tightening the axle nut, tighten the axle pinch bolt on by the axle nut. Then go around and pull back out on the other fork slider and let the slider move around on the axle and find its on position with no sticking on the axle. Then tighten that axle pinch bolt.
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  3. Twin headlight Ernie

    Twin headlight Ernie bar napkin engineering

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    How do you know if the bearing preload needs adjusting?
    2HE
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  4. supershaft

    supershaft because I can

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    The best way IMO is to make a spacer for your axled that takes place of the fork slider and torque your axle nut down with your axle in a vise and see how it feels. It takes some experience IMO. I have seen a lot of those bearings F'ed up for not adjusting them right.
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  5. disston

    disston ShadeTreeExpert

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    I think the axle nut torque is 25 ft/lbs. I'll look it up later.

    Tapered roller bearings are installed with preload on them. This means that the nut pushes on the bearing a certain amount. A plain ball bearing is installed with 0 preload but the design of the tapered roller bearing allows and demands the addition of a certain amount of preload. I think the actual preload is only 3 or 4 lbs, it might be a little higher but it is not the torque we are applying to the nut.

    The design of the axles provides for a calculated amount of wheel hub holding the outer races in place and the adjustment of the spacers on the inside, these are holding the bearings, adjusts the preload of the bearing. When learning to do this you will hear mention of the wedding band. There is a long spacer on the axle that the bearings are resting against. This is aided by the smaller spacer we call the wedding band that comes in several sizes. We can change the wedding band and sometimes add little shims to it or even lap the wedding band on sandpaper to make it thinner.

    I should go read this thing myself again. It is really a lot but Duane Ausherman covers everything, I think. After you read this you might have a better appreciation of what's going on with axles and wheels. It's good stuff to actually understand instead of just trying to blindly follow directions;

    http://w6rec.com/duane/bmw/wheel_bearing/index.htm
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  6. supershaft

    supershaft because I can

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    I do not recommend Duane's article. For obvious reasons IMO it has people thinking that the axle nut is a bearing adjuster nut. That and he goes on and on about how BMW shipped every bike out with tapered wheel bearings adjusted wrong. Wrong! I worked at a BMW dealer part time when those bikes were sold brand new. Complete BS! Our dealership and three neighboring dealerships that we were in constant contact with back in the day had no such issues.
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  7. Paul_Rochdale

    Paul_Rochdale Been here awhile

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    You Merrycans and your damned torque wrenches. Just do the nuts up. You'll know soon enough if you haven't got it right.
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  8. chollo9

    chollo9 Screwed the Pooch

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    No kiddin'

    Wait, I'm a Merrycan. :huh
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  9. chasbmw

    chasbmw Long timer

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    Most of Duane's experiance is with /5 and early /6 models, I think that he closed his dealership in about 1975, before your time SS I would guess.

    He has revised his site recently and it is well worth a read.

    He does not state that that the axel nut is a wheel bearing adjuster, but he does make the point that you can't tell whether or not the bearings are adjusted properly, unless thay are under load.

    Adjusting wheel bearings is one of those situations where slapdash Pommies might be advised to use a torque wrench:clap
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  10. supershaft

    supershaft because I can

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    I started working in a BMW motorcycle dealership in '75 the day after I quit my paper route but I already new the place pretty well for hanging out and working there on my dirt bikes and stuff. Besides Duane says all the tapered wheel bearing models came with maladjusted wheel bearings. As I understand it, he had what we would have called a ghost dealership after '75 selling new bikes to independent shops. If that was what was going on, sometimes a get a chuckle thinking about what the owner of my dad's dealership would have done to any poor smuck trying that in his retail area. There would have been a very high likelihood of some physical altercations. He was that kind of person and had a lot of experience with such stuff.

    He use to have people check the bearings with the axle nut. I think that was the start of the confusion. Then he would recommend not fully tightening down the axle nut. I have read many people reporting running loose axle nuts after reading his article and I can understand why if you didn't know any better while reading that article.
    #10