Snowflake balancing and wheel bearings.

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CaptAirhead
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Snowflake balancing and wheel bearings.

Postby CaptAirhead » Fri Jan 11, 2019 12:20 pm

A break in the weather let me have a crack at one of the last remaining jobs to do in an effort to get Lucy back on the road before Spring.

The plan was to get the back wheel off, get the new BT45 fitted then check out the bearings and refurbish the wheel. I got the front tyre fitted last year but didn't fit the wheel so as to make getting the back wheel off easier:-

ImageBMW R80/7 rear wheel removal by Ian Beat, on Flickr

The first part went well and the old Michelin Macadam cleared the bottom shock absorber bolt with a gentle tug. 5 minutes later, the wheel was in the local bike shop ( Murrays, Dundee)to get the BT45 fitted with the new tube. I went to collect the wheel yesterday and was informed that there was a slight problem in that the machine couldn't balance the wheel. I took the wheel home and checked out the bearings which I had planned to do anyway. The first thing I noticed was that the spacer and wedding band were both very loose inside and I could wiggle them around very easily with my finger. This of course meant that the pre-load was not right. Once I removed the seals it was obvious that the twenty year old bearings were shot. One was a bit rough and the other was rusty and barely moving. The races were in a bit of a mess too so a quick phone call and the new bearings were ordered and arrived this morning:-

ImageBMW R80/7 rear wheel bearings by Ian Beat, on Flickr

So, the next job is to remove the old races and fit the new bearings. Happily the Snowflake wheel has the steel insert in the hub so that's not a worry but I'll have to do some reading to figure out how to set the pre-load properly as I've never done this job before. Any suggestions and hints welcome.
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Re: Snowflake balancing and wheel bearings.

Postby barryh » Fri Jan 11, 2019 12:37 pm

There are two methods to set the pre-load.

One involves measuring the torque to rotate the wheel using a length of string wrapped around the spindle pulled with a spring balance. The other is Duane Aushermans shake the wheel test which basically involves torqueing the wheel nut whilst feeling for all play in the bearing being eliminated. The aim is for play to disappear just before reaching the recommended torque although you'll find which ever method is used, the shim sizes won't usually allow a precise setting. I find the latter method quite adequate and it improved the pre-load no end over how the factory had set up my bike which was with grossly excessive pre-load. I wouldn't obsess over it, The factory didn't and unless you lap the wedding ring, the shim size increments won't usually allow you to reach perfection.

If you don't have a balancing rig it's possible to do a reasonable job of balancing the wheel on it's own bearings. You need to wash off any grease and lightly oil the bearings which you should be doing anyway to set the pre-load.

https://w6rec.com/the-5-wheel-bearings/

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Re: Snowflake balancing and wheel bearings.

Postby CharlieVictor » Fri Jan 11, 2019 1:30 pm

Never balanced the wheels.
Never felt the difference. On either bikes. 8-[
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Re: Snowflake balancing and wheel bearings.

Postby CaptAirhead » Fri Jan 11, 2019 2:22 pm

UPDATE:-
Thanks for the replies chaps. I've drifted out the bearing outer races and cleaned up all the bearing components ready for refitting:-

ImageBMW R80/7 Rear wheel bearing stack by Ian Beat, on Flickr

I've popped the outer races in the freezer to make them easier to press in. While that is happening, I decided to give the brake drum a good clean as it was quite badly contaminated with grease and gunge ( it looked a lot worse before I soaked it with white spirit):-

ImageBMW R80/7 Rear snowflake wheel cleaning. by Ian Beat, on Flickr

Ten minutes later and the wheel was ready for the new bearings:-

ImageBMW R80/7 Rear wheel Cleaned. by Ian Beat, on Flickr

I've brought the wheel indoors to warm up and dug out my heat gun to help getting the outer races pressed in. While the races are cooling down in the freezer, time for a cup of coffee and reflect on the next part of the operation. I've read up on the Duane Ausherman shake method and it's very similar to what I used to do when checking car wheel bearings so that is what I am going for. The wedding band fitted is 6.75mm which is about middle of the road and hopefully, with the new bearings, I won't have to change that. I'm going to balance the wheel and check run out etc myself and have ordered up a selection of balance weights. I'll check the front wheel while I'm at it.
So chaps, thanks for the input and I'll let you know how it pans out.
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Re: Snowflake balancing and wheel bearings.

Postby windmill john » Fri Jan 11, 2019 4:39 pm

Never balanced the wheels.
Never felt the difference. On either bikes. 8-[

You're not going fast enough......

There's a lot of weight in an Airhead wheel, I imagine you'd feel the issue more with a lighter wheel; that's guessing by the way.
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Re: Snowflake balancing and wheel bearings.

Postby barryh » Fri Jan 11, 2019 7:55 pm


You're not going fast enough......

And it doesn't have to be that fast. At 70MPH an 18" wheel is doing approx. 912 RPM. In the worst case i.e. the out of balance being at the tread surface, 10 Grams out of balance produces a 3 Kg force. If the out of balance was at the wheel rim, the force produced by 10 grams would still be 2 Kg.
It's a square rather than a linear effect so the out of balance force diminishes rapidly at slower speeds. By 50 MPH the force is already halved.

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Re: Snowflake balancing and wheel bearings.

Postby CaptAirhead » Fri Jan 11, 2019 8:04 pm

Well the bearing outer races went in OK after freezing them for an hour and heating up the hub with the hot air gun:-

ImageBMW R80/7 Rear wheel bearing race. by Ian Beat, on Flickr

I test fitted the bearing pack on the wheel and even without any torque, it was obvious that the looseness in the spacer had gone and it looks like the pre-load will be OK when torqued up.

ImageR80/7 Rear wheel bearing Pack by Ian Beat, on Flickr

I'll check it anyway just to be sure but it looks like the job's a good 'un. As far as balancing is concerned, I can either do it myself or run it along to the local bike shop who will do it for free.

Next job re-assemble and test rear brakes.
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Re: Snowflake balancing and wheel bearings.

Postby Rob Frankhamr » Fri Jan 11, 2019 11:11 pm

I test fitted the bearing pack on the wheel and even without any torque, it was obvious that the looseness in the spacer had gone and it looks like the pre-load will be OK when torqued up.
How can you tell that the spacer is loose (or not loose). If you are looking at the components without the axle fitted, then you are getting a false impression. The spacer(s) should be loose. Tightening the axle nut forces the two inner races together setting the preload. Without the axle, there is no preload and all of the components will move about.

A lot of bike shops (and more particularly tyre firms) can't balance a twinshock boxer wheel. They don't have the right mandrels to load the wheel onto there balancing machines. Beware the shop that claims it can balance them on an automatic machine. If it's not correctly mounted, the wheel will move in relation to the machine spindle and the balance will be out .A long time ago, I built a balancing jig which allows me to do it manually the old way.

On fitting the wheel, be very careful tightening iot for the first time. If the preload shim (wedding band) is too small, simply tightening the nut to the correct torque can brinnel the bearings and you'll be back to square one. Tighten the nut progressively and check for resistance in the turning of the wheel, If it starts to get tight, stop and use a thicker 'wedding band'.

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Re: Snowflake balancing and wheel bearings.

Postby CaptAirhead » Sat Jan 12, 2019 12:27 am

I did state that I will check the pre load anyway using the method recommended by Duane Ausherman. Regarding the balancing, it had occurred to me that the tapered bearings may have caused problems with the balancing machine. The fact that the bearings were well and truly shot wouldn't have helped either. They did the front wheel a few weeks ago and didn't report any problem but I'll check the front myself when I do the rear. I'm currently working on a balancing jig which will load the bearings so the wheel runs true. I may have to knock up a couple of mandrels on the lathe but haven't worked out the fine details yet, I've been too busy upgrading computers for the last few days but I'll get round to it soon enough.
I'll try and check the pre-load over the weekend so it will be interesting to see if the current 6.75mm wedding band is correct or not. I'm guessing that it will be OK but if I'm wrong, I'll stand you a pot of tea and a sticky bun when we catch up at one of the meets.
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Re: Snowflake balancing and wheel bearings.

Postby Rob Frankhamr » Sat Jan 12, 2019 1:53 am

If it comes to the crunch, I have a bag of various size 'wedding bands'. Could always bring them over.

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Re: Snowflake balancing and wheel bearings.

Postby CharlieVictor » Sat Jan 12, 2019 11:56 am

Never balanced the wheels.
Never felt the difference. On either bikes. 8-[

You're not going fast enough......
Most likely.
You make me feel inadequate now. Quite unheard of for a Frenchman. :drunken:
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Re: Snowflake balancing and wheel bearings.

Postby Roy Gavin » Sat Jan 12, 2019 1:19 pm

Cycle Works in the US sell shims which let you dial in the gap if you have a undersized wedding band, and also a tool to grease the bearings easily.
Or they once did, tales on the net of problems lately.
All taper rollers need a little preload, Vincent's with a similar set up nominate 2 thou, which is around 1/4 of a flat turn from first touch on the axle nut.
But as that first touch should be when the torque on the nut is around 20 ft/lbs a delicate touch is required, as Rob has already pointed out.

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Re: Snowflake balancing and wheel bearings.

Postby barryh » Sat Jan 12, 2019 1:49 pm

I've always wondered why taper roller wheel bearings on cars typically have a small amount of play prescribed. Thinking about Duanes bearing diagram where point 3 is optimum but somewhere between 1 and 2 is not so bad, the cynical in me thinks it might be because play is much more easily measured by the average mechanic which is at least safe while pre-load is not so easy at all and if done to excess potentially dangerous. Anyone know if there is another reason like differential thermal expansion but it's all steel isn't it. Or is it simply that car wheel bearings have no means of controlling the pre-load by spacers that oppose the torque of the nut.
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Re: Snowflake balancing and wheel bearings.

Postby Roy Gavin » Sun Jan 13, 2019 1:42 am

Are we talking castellated nuts and split pins here?
If so the answer might simply be tolerances as - up to touch and then tighter up to the next pin slot - would usually overload the bearing.
Cars wheels usually have toe in too - so there are always more forces acting on the bearing than there might be on a bike wheel.
The brakes have a bit more work to do on a two ton car, so there is a lot more heat to transfer into the hub and they are probably less well cooled than exposed bike brakes so expansion may be a factor, probably a bit of all combined.

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Re: Snowflake balancing and wheel bearings.

Postby barryh » Sun Jan 13, 2019 11:36 am

I remember the castellated nuts and split pins on my early cars but on the Mercedes cars I've owned over the last 25 years they have used a nut that has a pinch bolt to clamp it in place. Adjustment is infinitely variable and yet they still specify .4 to .8 thou of end float. That is so small and difficult to measure I generally aim for close to zero. The amount of end float being so small still makes me think they are just playing safe. I doubt it would be possible to measure preload on heavy greased bearings even if that was the optimum setting.

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Re: Snowflake balancing and wheel bearings.

Postby Roy Gavin » Mon Jan 14, 2019 3:16 am

Ye gods, first bike bloke I have met who doesn't think he can measure to 1/2 a ten thou with a $20- gauge, or lives in a world where everything is made to zero tolerance, +_ nil!
Yes, the last time I did a car wheel bearing was a long time ago, bearings and lubes have improved a bit since then and doesn't seem to be needed as much nowadays, particularly if you can get it closer at the initial setting with something better than backing off a castellated nut.

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Re: Snowflake balancing and wheel bearings.

Postby warmshed » Mon Jan 14, 2019 10:36 am

I believe that Timken bearings used to say that you should not preload their taper bearings. Velocette use a 4 thou preload on their crank main bearings and were at odds with them. The idea was that when up to running temperatures the cases expanded to get to the no preload sate.
When setting up the preload make sure you do NOT grease the bearings, they should be clean and lightly oiled, just as supplied.
When you have finished the preload, this is the time to balance the wheels, ie without any grease and without the oil seals fitted. This will enable to balancing to be more accurate without any "stiction".
Once balanced that is the time to remove the bearings and apply the grease then seals.

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Re: Snowflake balancing and wheel bearings.

Postby Roy Gavin » Tue Jan 15, 2019 1:14 am

The advice to preload taper bearings was on the Timken site last time I looked , but no figures were given.
BMW advises preload on all the taper roller bearings on airheads, as do Vincent and Velocette, so it is a big call stating that they are wrong!
The graph previously posted actually shows bearing life higher at 2 thou preload than at one, and a life at 2 thou if properly treated that would take you over a couple of million miles, which is probably going to be enough to see most out!

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Re: Snowflake balancing and wheel bearings.

Postby warmshed » Tue Jan 15, 2019 10:50 am

The graph shown in earlier posting is different from the one on the Timken site, "near zero to slight preload" is now listed as maximum life. and at 4 thou prelad the graph hits the base line, hence why Velocette with their 4 thou preload raised eyebrows. Thermal expansion is the key here, often on wheels the hub can expand and give a high preload, some less, that's why \i feel that the manufacturers figures should be followed.

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Re: Snowflake balancing and wheel bearings.

Postby CaptAirhead » Tue Jan 15, 2019 12:05 pm

Found these 0.2mm shims on eBay. They may ( or may not) come in handy when setting the pre-load. Although Probably not, they are around 7 thou or thereabouts. Could do with finding some at around 1 or 2 thou.

Image0.2mm shims by Ian Beat, on Flickr

If not, they will be useful for something else,
Ian.
Last edited by CaptAirhead on Tue Jan 15, 2019 12:14 pm, edited 1 time in total.
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Re: Snowflake balancing and wheel bearings.

Postby Roy Gavin » Tue Jan 15, 2019 12:14 pm

https://www.timken.com/wp-content/uploa ... df#page=68

As a post script some light reading for anyone interested if the fact of the matter


Warmsled,Velos seemed to last OK with 4 thou preload, they still hold the 24 hour speed record for 500cc bikes, almost 70 years after they set it.
And Vincents got along nicely too, with 2 tho reload on their wheels- never heard of one failing, even at 150 MPH ,a record they held for 60 years.
Amazing how the managed that when they didn't even know as much about motorcycle engineering as you!
Remind us, how many world record holders have you designed and built -three is it ?

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Re: Snowflake balancing and wheel bearings.

Postby barryh » Tue Jan 15, 2019 1:41 pm

Found these 0.2mm shims on eBay. They may ( or may not) come in handy when setting the pre-load. Although Probably not, they are around 7 thou or thereabouts. Could do with finding some at around 1 or 2 thou.
BMW supplied the wedding bands in 0.05mm or approx. 0.002" increments and in my opinion even that is too big to get the pre-load where I would want it. 1 thou would be better. I finished up making my own shims which was a pain but I preferred to do that rather than having to buy and then lap a larger wedding band.

For what it's worth my bike survived it's first 28 years with the factory settings of 4 thou pre-load on one wheel and 2 thou on the other but boy could you feel the difference when they were reduced. I swear it felt easier to push the bike around the garage.

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Re: Snowflake balancing and wheel bearings.

Postby CaptAirhead » Tue Jan 15, 2019 2:44 pm

Well it'll be interesting to find out how the pre-load works out but it's just too cold, wet and miserable to go outside and find out. The weather forecast doesn't look too great this week so I'll just have to find some inside jobs to do. Even the cat won't go out today:-

ImageFatpuss by Ian Beat, on Flickr

Roll on the Spring.
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Re: Snowflake balancing and wheel bearings.

Postby warmshed » Tue Jan 15, 2019 4:31 pm

Roy Gavin, You did not read my post correctly, I said Velocette used 4 thou preload but then added take the manufacturers(velo) advice and thermal expansion plays a part. The velo cases, at running temperature, have next to no preload, even so bursting through the drive side cases is not unknown. The later cases were thicker and tempered to fix this. I own a Venom Clubman and a Thruxton so do have some knowledge in this. I have not stated I am an expert and think your replies are unnecessarily tinged with aggression? why? we are trying to assist someone with their restoration.

Back to the original post, renovating my bike I turned my own wedding ring fraction longer than the BMW one and faced it off in stages to get the correct preload, saving the need for shims, as you say you have a lathe you might find this way suits you. I used the string and weight method as per Snowbum and am pleased with the result, you need to turn a spacer the correct OD to do this but not hard to do.

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Re: Snowflake balancing and wheel bearings.

Postby CaptAirhead » Tue Jan 15, 2019 6:02 pm

@ Warmshed: Yes, I suppose turning a wedding ring to the correct dimensions may be a possibility. Since the weather is against any outside work, I may have a look and see if I have any suitable stock. I'm not particularly experience at turning but a simple wedding band should not present too much difficulty. However, the question is quite academic until I can get out and check the pre-load with the existing wedding band and the new bearings.
That may not be anytime soon according to the weather forecast. At least I am well on schedule to complete the rebuild by the Spring with only some minor wee issues to sort out. The most pressing, apart from the pre-load check, is the wear on the gear change pivot which I will have to shim. Once done, it is only a case of checking torque settings and going round with the grease gun and that , as they say, should be that unless something crops up on the road test.
Ian.
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