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Old 09-12-2009, 04:23 AM   #1
woody's wheel works OP
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Joined: Jun 2004
Location: 39*40'33.86N 104*59'54.69W
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BMW F800GS rear wheel Bearing failures and solutions

FYI,,i was lurking in the new posts this morning,,,Ya'll have a serious problem going on so i'm posting this in the hopes it may help all of us getting to the bottom of the rear wheel bearing failures,,

there was so much speculation and mis-information and groping in the dark that i decided to help you all get a better handle /understanding of what you are up against...PLEASE remember there is nothing generically wrong with BMW's basic design or the 6204 bearing used...

On the outside possibility that it was a bad run of bearings,,[highly unlikely] we can better trace that by you all collating the following info ie:

A,,sprocket carrier bearing/brand
B,,inner bearing of hub/brand
C,,outer.disc side bearing/brand

then we can ascertain if bad bearings are the cause that yielded the chronicled effects...

FYI,,what i failed to mention in my PM to tmex was the incredible importance of the proper bearing bore size in the hub itself,,,the lil bit of info relating that the disc side bearing drops in partway and then needed hammering in the rest of the way after the hub was heated and bearing frozen,,get's my crap detector going BIG WTF TIME..properly dimensioned bores allow the bearing to BOING drop down all the way....tis a thing of beauty heat and favorite technique,,,,no chance of ruining your bearing

a rough rule of thumb i use in building my hubs is .0005'' per inch of bore,,so that would equate to circa .001'' for a 6204 bearing.. any smaller bore size would invariably yield notchy/crunchy bearings. hence ,,you could check this easily by taking a new nice n smooth turning bearing ,,,installing it per factory guidelines ,,letting the hub cool to room temp ,,turn the bearing with your finger,,, it should be smooth,,,if not you have located the problem.....,,realize there may be other issues as related below,,,

I just realized IF the bearing bore is the problem ie too small ,,ya'll have a major problem on your hand,,since there are NO wheels OR hubs available as of this minute,,, the Rx would be to re-bore the hub, a good machinist in your neck of the woods could possibly handle this on a mill.,,we routinely perform that service circa $60 per side plus parts and $20 bearing R&R...any guinea -pigs in the denver area,,,come on by and we'll check this out!!!

Some inmates have asked how much to do this: $99 Advrider special both sides speced to .001'' and a pair of doubles sealed bearings..will install yor pick up your parts from BMW or your favorite bearing house if it is important to you...

OK,,,here's a lil tip for you bearing installers,,,often after hammering/pressing in the bearings,,you test the bearing and WTF !!!!they are binding /notchy,,panic not !!!you may have a tiny bit of pre-load on them,,just insert the axle give it a slight rap with your hammer ,,do the same from the other side and VOILA 90% of the time your bearings will loosen and feel just like you had hoped for!!!

OK,,,here's the gist of a PM i sent to tmex and his thread; if this data doesn't make it over to his thread[i can not post outside of vendor forum],,,then possibly some F800GS owner could let the guys in that thread know we are working on a solution to their problem by getting a post or link established...this problem needs to be solved ASAP before someone gets injured!!!

first i empathize for all you bmw riders with issues like these motorad is notorious for sandbagging and not admitting culpability for fear of litigation and having recalls is a given with these folks..

ok,,here's what you need to keep in mind....

1. 6204 double sealed bearings regardless of manufacture have been used by everybody on front and rear wheels for a long time without any major issues...true some don't have as much grease as others,,,we know which brands are skimpy,,, and routinely repack them with upgraded hi-temp wheel bearing grease,,,and for dual sport adv riders even offer waterproof grease for the water-crossing species,,,so the odds are against you looking to the bearings as the culprit....

2.cocked bearings would be fairly noticeable and show signs of wrong installation in the one has noticed or reported eliminate that too.

3,here's where it gets interesting,,,there are two basic approaches to wheel-bearing set-ups.,,,i'll call them:

type A,, probably the most common,,,uses precisely machined lateral flanges on the ID of the hub to locate the inner spacer is used to prevent crush when tightening all the components /spacers on the axle... this spacer needs to be minimally .010''+.002-.000/steel or .020'' +.003-.000/aluminum to be effective.... so the hub essentially has a little bit of lateral float built in... a simple elegant fairly bullet-proof technique which fails only when :

a,,,the manufacturer uses too soft axle spacer BWOE KTM several years ago on the rear dirt bikes,,too much torque would crush them resulting in many blown up rear hubs

b,,someone specs a spacer the same size or smaller than the inner lip dimension.,,has happened,,,but highly unlikely!!

type B,,used by Kawasaki,Honda,BmW,Triumph etc, uses some means of retaining one bearing on one side [usually the side where the disc brake is on. ie to make sure the wheel consistently is spaced /aligned properly with the disc],,Kawasaki,KTM and BMW routinely use a circlip to retain that bearing in place,,,honda and triumph usually use a nut to hold it.,,,what usually happens next is that on the other side the bore in the hub often doesn't have an inner lip or the lip is usually bored far deeper than the width of the inner spacer...VOILA you have no worries about proper inner axle spacer dimensions because the bearing should self adjust....

FYI..notice this leaves the captured bearing be responsible for all the lateral loads imposed by that wheel,,,this technique is usually utilized for front hubs,,,although i have seen it on some honda rears BUT for lighter machinery dirtbikes the bigger stuff ussually had bigger/beefier bearings installed on that this could be an outside probable cause for the disc side bearing going bad

Rx,,,,this would leave the following areas to be scrutinized in my estimation:
1..the simplest is to first ascertain if there is an inner lip on the side opposite of the captured bearing....if there isn't well we have to look somewhere else,,,,IF THERE IS,,,install the captured bearing first ,,,get your calipers and measure the distance from the bearing to the lip,,jot i down and then measure your spacer,,like i wrote HAS TO BE LONGER minimally by those specs!!! if it's smaller or the same well you are on to another probable cause of your symptoms and their consequences.

2,,FYI i'm inserting this here as an edit .. the next probable cause has to do with too tight bore,which i discussed in detail above and IMHO is the first thing i would be checking!!

3,,the last probable cause is a matter of improper bearing installation...BWOE,too much pressure creating preload conditions symptomatic of some of the observations of the fellow who cut up the bearings ,,,or BWOE that if in type A the spacer was too big as well as type B...IF the bearing installer had his stops wrong and compressed the outer races beyond the inner spacers dimensions

hope this shines a little light on the subject,,i'll double check the next rear wheels i get and report back in....

OHHHh,,,heed the advice of the fellow who suggested you all get BMW to do the work,,he's ABSOLUTELY right,,until you get a work order written up by just minimizes their number of ''problem cases'',, it' is counterproductive to fix their problem on your time and dime....

i can rest assure all i am on your side and will assist getting to the root of the problem...i'm fairly positive that the above info should put you on target .

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woody's wheel works screwed with this post 11-06-2009 at 09:24 AM
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