wheel bearing pre-load question

[gtgt_bangbang]

Not sure I have the patience or the fixturing to do my first guess of proper "pre load spacer" in the usual process ; namely "assemble the wheel with best guess shimming and weigh the break free loading with strings and scale."

I probably still do that as a final check, but sure seems there is a physical INTERFERENCE range that would get the preload real close ,
and not all that difficult to do with the wheel on a bench.

My question is ; does anyone have a value for the the interference range , in other words how much " crush" is correct for proper bearing preload?
The Crush in DISTANCE, not break free load ...

I figure proper interference / crush will be nothing less than zero (must have actual contact through entire spacer stack ), and upper tolerance at some extremely small interference value.

I plan to swap in various shims while measuring the upper bearing recess, the depth in hub , with a depth mic , to find when it raises a fraction of a mil off its race.


Not clear? as if MORE words will help, ;

I drove both bearings outer races in , with the original distance piece & wedding ring inside ( I'll skip heating the hub next time; its useless with that steel hub liner , but it did help melt some of the distance piece plastic spools, so now the distance piece will be a little sloppy , come time to insert axle...


I set the wheel horizontal on a stable flat surface , with inner bearings inserted , and with a socket under the bottom side bearing to force it up in the race, seated like normal. iow, The wheel is sitting horizontal and able to spin on the lower side bearing.


Then , I measure how "recessed" the inner race of the TOP bearing is in the hub.... ( a depth micrometer will do great , or calipers on a stiff bridge across the counter bore.)

Now try various shims until the upper bearing rises just barely rise off the race. I figure a fraction of a .001 would be enough crush ....sure would like ot know though ...


This is working cos at the start of my set up, using only the old spacer & wedding ring with the new bearings, it is obvious the the spacer stack is NOT in contact with both bearings, so I need to add stack height , iow, my spacer stack is starting with a tiny bit of a gap.


knowing that bearing life is much better when slightly OVER (pre) LOADED (some small positive interference) than UNDER pre LOADED ( no interference, a slop condition), Ill err on the side of higher crush , need be.

The proper crush should be measureable, ANY ONE KNOW IT ? many thanks

 

[6322]

I’ve wrenched on airheads for fifty years and have never found plastic, distance spacers in the wheel bearing assemblies. Using the proper, existing steel spacers, wheel bearing preload is applied when torquing the the large axle nut to the proper specification.

 

[gtgt_bangbang]

there are 2 PLASTIC SPOOLs , little off-white thingees in my snowflakes , which fit snug around the distance piece ( the ~2"ish metal tube) inside every airhead wheeel you ever looked at , afaik, see example; pn 36 31 1 237 595 ok bmw calls em RINGS. They sure spooled me !


Im talking about the one spool that hangs off the end of the distance piece a little bit, keeps the wedding ring (and any shims) from bouncing around the hub ,
and both spools have little ribs around them that keep the distance piece ~somewhat centered up~ inside the hub, to help the axle pass through the distance piece .

I melted one a bit with the ol heat gun, trying to expand the wheel hub, to help fit the bearing race in wheel.
my " there be dragons" warning was - It wasnt worth it ( fitting steel in steel ... the outer piece would need to be EXTREMELY hot to work, the CTE is so low) ) but never mind , thats not the issue anyway. I pounded em assisted by my dandy Plate Puller !



it is clear how these wheel bearings assemblies actually work ?

The OUTER RACES ( plain races) are fixed in the hub; held a fixed distance apart from each other (which will only vary a little bit, as the hub heats & expands .. the crush wil be less when the hub heats up, ANOTHER reason to run a bit more interfere I suppose )

This means the INNER RACES ( roller races) are also going to to sit at some fixed distance apart , when resting full "home" in the outer races.

If there was NO (or too short) distance piece inside ( forget the plastic for awhile) , torquing down the axle nut would push the inner races inboard ,
crushing them into the outer races, limited only by how tight ya can crank the axle nut. Not good for several reasons.


So The DISTANCE PIECE inside ( plus wedding ring & any spacers) is a solid stop , resting against the roller races, blocking unwanted / excess inboard movement.
The DP takes on most of the load from the nut/axle squeeze.
The rollers should be bearing some , but not all of the nut / axle compression load.

I assume a zip point zero clearance fit is actually best, but thats hard to guarantee or maintain, so some limited tiny bit of crush is next best..
SO the fit has to be somewhere between ZERO play and juuuuuuust right, which is probably a fraction of .001" or so, I'd guess. but I dont want to guess.
And too-tight is better than too-loose , within reason (take quite a GRUNT on the nut to really dent a bearing but the lube issue costs life)

Just wondering if someone ever heard of the wheel bearing pre-load (this amount of crush . the amount of interference fit , which is technically the "pre-load"

I want to set my wheels up on the bench, swapping shims in/out until the bearings just begin move apart measurably
( measurable the way I was describing ;supporting wheel horizontal , resting on the lower bearing complete, and measuring the depth of the upper bearing which will vary with the distance piece stack height.

actually I dont even want to use the shims in the finished wheel since they are getting rare, I just want to use them to determine the correct wedding ring and I'll buy those , there are supposed to be scads of heights available.

 

[slowpokepete]

Not sure if this is what you need or what you are trying to avoid, but Brook Reams posted this a while back...

https://www.youtube.com/watch?v=l-AmUmOissM

SPP

 

[gtgt_bangbang]

thanks, am familiar with the concept,

Im not doubting its possible to indirectly measure the "PRE LOAD"
(fact; we REALLY want to know is the bearing "crush" or interference fit , within the fully installed, wheel-on-bike , assembly)
by directly (but , with low accuracy & precision) measuring a "break-free" force (ok; break-free TORQUE , for pure-ists).

But you STILL need to pick the "correct" wedding ring / spacers/ shim / whatever you want to call them to begin with,
( im going to name it here a DPA , Distance Piece ASSEMBLY, consists of the Pipe + wedding ring + any shim-stock spacers) - ,
then you get to assemble the axle & string , yadayada , and perform the rough & coarse but admittedly inaccurate "pull my stringer" test with a Not-Accurate-For-Trade fishin scale.

Im gonna try take That Hill by saying ; its prolly better & easier to measure the interference fit of the bearings.
by conveniently measuring the actual interference of the bearings , for instance use a depth micrometer.


MY bench-top set-up will lightly seat one bearing "home" (seated into its race) , by placing the wheel horizontally and supported only through the 'lower' bearing ,
using a block / socket / ect placed between the lower bearing & table.

Then , placing the other ( top side ) bearing , also just "sitting home" in its race,
its easy to accurately measure the RECESS DEPTH of the TOP bearing [/B (with respect to the hub bore LIP ) .
Easy with a depth mic anyway ...

THIS arrangement will be the " ZERO CLEARANCE" ,or perfect-fit, for the bearings, assuming no contact between the DPA & both bearings.

The wheel Im working on now , with new bearings & previous DPA stack, the DPA is now too short
(excess clearance, would cause the mis-named "preload" or BREAK FREE TORQUE to be too high when built).

You can actually see / feel this clearance, using a little probe to push the wedding ring back & forth , inside the hub, with no axle inserted. Loose slip fit.

By swapping shims into the DPA ( I have a few of those shim-stock rings, like .005, .004 .002" thick rings ) I'll be able to measure - directly-
at what point the increasing length of the DPA finally contacts both bearings, by measuring the top bearing lift up in bore from the contact.

Since these shim stock rings are currently NLA, I'm not going to permanently install any in the hub, I just want to use as measure tools,
determine the ideal height / determine the correct wedding ring, & try to order that up.
MAXBMW indicates they have a stash of wedding rings in various heights.


So my only question was ; has anyone come across the correct (linear measurement) , the proper amount of " CRUSH" ?

If not . I'll guess

A taper bearing runs near its 'best' ~ basically max life, equal to a few million miles or dozen of Bike Lifes, when running a true ZERO clearance.
It will be kind of hard to hit & maintain that zero clearance though ...

With TOO SHORT of a DPA ( clearance > 0) , the rollers will try to crush into the races, perhaps excessivly, when loaded up by axle nut.
The wheel bearing & race is definitely hard/strong enough of metal to NOT be damaged with some degree of interference / crush fit,
and I've seen mfgr's graphs showing some amount of EXCESS CRUSH is better than INSUFFICIENT crush.

With TOO LONG a DPA, the bearings wont be crushed, but being too far apart, will have some slop between rollers and races,
perhaps to point of wheel wobble or unusual wear. wont take much when the slop is multiplied by the wheel radius.




for NErDs OnLy

another consideration; the thermal expansion of the aluminum wheel hub.

Assuming the bearings are held apart by 70mm of aluminum hub,
and with a ball-park aluminum Thermal Expansion Coeff. of 23(10^-6) M / M*C,
and pretending the brake discs are able to heat the aluminum hub to 100C , ( anybody know the usual hub temperature ?)

thus " hot " wheels will force the bearings to move APART a bit under 0.001".
The (steel) DPA expands about 1/10 that much, ~ negligible .

In other words, a near 0.001" of interference / crush at room temp is justified just to keep the bearings in a state of actual "pre-load" during hot running.

I'll assume a small fraction of a 0.001" is an acceptable crush just out of respect for bearing material strength,
but adding ~ .001 crush for thermal effects,
and just roll with it, nyuk nyuk nyuk


non-nerds warned off again ;
not to burrow too deep, but the dynamic method a ( fishin scale & string) actually (attempts to) measure the tug required to transition from stopped (a state of static-friction) to a moving condition ( here , call it "rolling" friction, cos it aint either exactly static or sliding friction . )
Maybe with a "max reading" slide, which adds its OWN error, blahblah

or better yet (and much more difficult to perform) , should be reading the constant force required to keep the wheel rolling at steady speed.
again very difficult to do "right".

 

[melville]

This has been my go-to process for BMW wheel bearing adjustment:

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

The plastic bits you were dealing with were added for the later models and are not strictly necessary but they do make life easier.

I'll be doing this soon on some snowflakes on my 1979 R100RS.

 

[nickrides]

For the Ultimate, lengthy, long winded, verbose, detailed, repeated 10x, in-depth, detailed, endless monologue, sleep inducing, repetitive, long winded, endless, did already say endless? sorry, discussion and direction on BMW Airhead Wheel Bearings I suggest doing a Acapulco style swan dive into:

Snowbums website

https://bmwmotorcycletech.info/

The Go to Place for everything Airhead

gtgt this might be right up your alley.

Nick
zzzzzz

 

[gtgt_bangbang]

For the Ultimate, lengthy, long winded, verbose, detailed, repeated 10x, in-depth, detailed, endless monologue, sleep inducing, repetitive, long winded, endless, did already say endless? sorry, discussion and direction on BMW Airhead Wheel Bearings I suggest doing a Acapulco style swan dive into: Snowbums website

gtgt this might be right up your alley. Nickzzzzz

RIGHT ON DUDE ! go for a ride, instead .

I balled the Hecker Pass today over in to Watsonnville , then homelegged a darm near empty 17 North from SCruz to SaintJoe on a 400 CVT Maj. freekin sublime.
Scrubbed the chicken strips up a bit. not my bidness to spend your time, but maybe read The Hobbit first, then 'Da Return Of Da King 'will make a lot more sinse

 

[gtgt_bangbang]

For the Ultimate Nick zzzzzz

lolz

 

[craydds]

The proper crush should be measureable, ANY ONE KNOW IT ? many thanks

Talk to Woody about this. https://woodyswheelworks.com/collections/parts-tires .
He will get you fixed up. He has new bearings that totally eliminate any worries about "pre-load", etc. I have two pairs of wheels (R90/6 and R90S) that Woody will be rebuilding. This will include brand new the brand new bearings, etc.

 

[gtgt_bangbang]

[ed]

 

[stevenrankin]

Airheads Club

You may have better luck getting answers in the dedicated Airheads Club forum. St.

 

[gtgt_bangbang]

LOL didnt really need any answers , but sure got a lot of them for questions I didnt ask , or even have !
no worries, sometimes feels good to let the kids sitting in back get more involved with a thread ¯\_ (ツ)_/¯

did a little read up on bearings ( some site that dont expect Identifying as an Airhead to be there !

wrap up schmeer -

Zero clearance is ideal. ie spacer (pipe+shim ) = exactly bearing-to-bearing "B2B" distance,
ie axle nut torque doesnt "crush" through the rollers bcos the spacer supports races

Bearing in "crush" (interference fit) is usually next best. ie spacer < B2B distance. A loose slip inside cold wheel. .001" short (or a 1/2 thou PER bearing) is fine.

Bearing itself runs fine w/ slight slop , (pipe + shim > B2B distance ), but not every application has a tire whirling around it , so I'll aim for 'crush" mode.

Hub Thermal Expansion will increase bearing-bearing spacing in wheels, maybe ~0.0005". This has effect that the pipe/shim "act shorter " so adding length to counter.

With the depth mic and a little trick set up and a few of those very thin shims, , its easy to measure these numbers and have eng.fun doing it ,
I have to thrash out all those rules bcos some of the signs (+/- effects) almost seem counter intuitive.

The depth mic was best $25 I dropped in awhile. bless craig and his little list.
Prolly cheaper than a crappy scale with few gram range no good for nothing after this task except a minnow tournament fishing.

( some day Ill maybe trick guys into reading, okK maybe not , how to use one of those cheap ass HF digital scales to measure low gram torques! ;
it worked pretty cool setting up a axle with out a spendy micro range torque gauge..

Linear measurement (ie a mic) set up is way better than dynamic or torque tests, which do indeed correlate to bearing preload , but while "easy" to do is hard to do 'right'
if you understand whats really going on. Reading a steady state moving spring scale ... hm

BMW made shims / wedding rings on .002" / 0.05 increments, implying their set-up Specs were limited to +/-0.001" .
Almost guarantee THEY were using mics of some sort LOL

The pipe & shim stack NEED to be dead square ends or all bets are off, & again why bother . Worth checking.
On of my shims was off square, some body probably diddled sanding it on a kitchen table .
Anyway really helps to know the exact spacer to peg it; dont know how to get that number without measuring.

I'll prolly target a slightly sub 0.001" spacer gap (aka ~ . 001 bearing crush) .
and finally its not my bad if you read this far but didnt really want too;

 

[pglaves]

After I bought my first K75 in 1986 I gave up needing to bother with this esoteric nonsense of sanding or grinding little spacers to properly install bearings. Never had to do it on any car I owned either, going back to a 1953 Dodge. German engineering might not have been all it was cracked up to be.

 

[henzilla]

Hey, what happened to that “simple by design” thing

gt, it’s what we do… enjoy

 

[stevenrankin]

miles

in the few times in 50 years and over 200K miles on one bike alone, I have never spent a whole lot of time fussing with such intricate measurements of bearing pre load the couple times I have had to change wheel bearings. I followed directions in the Chilton's manual. I have yet to have a failure of a wheel bearing or wheel.

While not a member of the Airheads Club, I like their motto, "Simple by Choice". If I had to resort to space shuttle tolerances and procedures to keep my two bikes on the roads, they would have been long gone and replaced with a dealer serviced unit.

Then again, everyone has their own thing and ways to do things. St.

 

[gtgt_bangbang]

Hey, what happened to that “simple by design” thing

gt, it’s what we do… enjoy

the happy sage Confuz Dem says
there is simplicity in perfection .


and perfection in simplicity
https://www.youtube.com/watch?v=_whFGulmKbU

 

[migrant]

My R90S came with Lester wheels installed. The seller also provided the original wire wheels. I'm in the process of swapping out the wheels and installing new wheel bearings. I bought the tool for removing the front wheel outer races and a couple shim kits from Cycle Works.

https://www.cycleworks.net/index.php?main_page=index&cPath=29_51

Starting with the rear wheel, I used the method found in this video for setting preload...using "moderate" two-thumb pressure to slide the outer spacer. Boxer2Valve also covers this method in their videos.

https://www.youtube.com/watch?v=IXj01hUKJBg

https://www.boxer2valve.com/bmw-r906-airhead-2-valve-tutorials.html

The front wheel required buying the proper length spacer that fits between the inner races. The Lester wheel had been installed with a custom one-piece spacer that was too short for the shim kit to resolve for the wire wheel, and too long to be used with a wedding band and shims. I found the proper spacer at EME along with the bearings and seals. If I had access to a lathe, it would have been easy to cut the spacer to the proper length.

Setting the preload using only measurements obtained through depth micrometer and stack length (outside mic) can get me close to the desired dimension, but at some point I have to involve my personal "feel" to accept the job I've done. That's where the .002" shims come into play.

 

[gtgt_bangbang]

in the few times in 50 years and over 200K miles on one bike alone, I have never spent a whole lot of time fussing with such intricate measurements of bearing pre load the couple times I have had to change wheel bearings. I followed directions in the Chilton's manual. I have yet to have a failure of a wheel bearing or wheel.

While not a member of the Airheads Club, I like their motto, "Simple by Choice". If I had to resort to space shuttle tolerances and procedures to keep my two bikes on the roads, they would have been long gone and replaced with a dealer serviced unit.

Then again, everyone has their own thing and ways to do things. St.

well thats explains a bit - you're a Chilton man !
prolly more comfy with threads that read like " 1) Removal is Obvious and Easy. 2) Reinstallation is the Opposite of Removal. 3) Find a local Specialist. "

Meanwhile I learned to read by recycled oil lamp with just the Haynes Manual Method, where "every manual based on a complete teardown & renovation! "
(if too often written with a Oxford accent!). I swear , first time coming across " Open the bonnet with a two handed grasp and insert your spanner" , I nearly lost it

Heck, some of those early Haynes manuals were just so darn good, I'd get the book first, and if I liked how it ended, I'd run out to buy the matching vehicle!

Thats a lot of miles though. Very Cool. I haven't ridden near as many miles let alone stay loyal to one machine , nevertheless a long time ago I figured it out ;
if I drove down a road by my own free choice, and the road didn't make me happy as I thought it would, that it was a DRIVER error, and not a problem of the road builder.
HE might have have been headed somewhere I didn't know or care about. Pretty much same same with my threads; if your experience and wisdom renders them boring or useless, feel weclome to skip on by, maybe re-re-review ol'time honored Best-Of threads instead of my fresh blatherings.


Im just writing to enjoy the act, same reason for building this BA beemer; This is my bike; there are many bikes like it, but this one is mine !
And if you kept yours running to da moon & back with naught more than a satchel of hard biscuits and some channel-locks, well thats a pretty cool hand my Lukes.

Still out of respect for the neighbors; if any one knows where to find the check box that DOESN'T force reluctant readers to visit my posts, who then not only want their 3 minutes of life restored after reviewing, but also feel compelled to dump MORE precious time into pounding out a " I really didn't want to read this" reply, then share with the Board pls.


I started many blurbs back up there ^^ with a "inclusive" softball question about a spec, (which was located via 10 seconds of duckduck'ing, cos F Google) ,
and between scowling "what you wanna mess with that river for, boy?" or instructions how to find easy to-find & already-well-trod Classics that didnt address my lil Q anyway, with the implication that " every thing possible to invent , has already been invented" , a bold statement that didnt age well for the Patent Office either.

But RE: measuring an interference fit with, gasp ..... a micrometer ! .... thsi is not what I think of as "Alien Technology " .
If it feels like it, free advice (& worth the price!); head down to that magical place called Harbor Freight to see for self the rows of 20 buck plastic digital calipers BEFORE cracking the spine on a Mitutoyo catalog !

While just measuring spacers in situ (instead of guessing with muy gusto & Go-Fish methods, lol) is easier & more enjoyable for me personally (as one who paid my dues and posts my crap for free) and better too, but only according to the people that make taper bearings for a living, I dont recommend it for anyone else , BUT if you insist trying an other worldy method like this, maybe I can save somebody a few minutes set up time and fire off a few fun jibes too.

 

[stevenrankin]

Insult?

well thats explains a bit - you're a Chilton man !
prolly more comfy with threads that read like " 1) Removal is Obvious and Easy. 2) Reinstallation is the Opposite of Removal. 3) Find a local Specialist. "

Hey pal, I read the Chilton's books and Hayes and BMW books on repairs back in the day when there was no internet where every one regardless of experience or smarts can make mountains out of mole hills or mountains into mole hills.

I have been reading and responding to your posts and to be honest I don't think there was a need, even as a jest, to be insulting in your reply to me.

I don't see at any point where I insulted you. I first suggested you might get better answers at the Airheads club forum, They cover "airheads" and have a larger data base and and number of members who turn wrenches on these bikes. Second I gave you MY experience and MY opinion. Saying on the forum I like the airhead motto Simple by choice is NOT an insult to you and if you take it that way, I am sorry for you. It is far different form the crap you wrote that I have copied here. St.