Front Wheel Bearings

[No_Twilight]

I have the folloing specs for front wheel bearings:

 

Front left wheel bearing 25 X 52 X 20.6 3205.2RS, 36.31-2 310 972

Front right wheel bearing 20 x 47 x 14 6204.2RS, 36.31-2 310 520

 

The left bearing is shown as 25mm ID but the axle is 20mm and I have one of these bearings in my hand and it is indeed 20mm ID. There appears to be a sleeve pressed into the bearing? If I order one from BMW will it come with this sleeve or do I need to press it out and reuse it? I don't like pressing against the balls like that.

 

I was just about to order a replacement bearing from bearingsdirect.com for $15 vs $30+ from BMW. And I bought some very nice right wheel bearings on E-bay for $1/each. They were the same manufacturer (skf) as the ones I took out.

 

I'm thinking that if I need to provide the sleeve I'll just make one myself and loctite it in instead of pressing it. I can always easily achieve a better that .0005" fit which is much better than the fit on the axle. Thanks,

 

--Jerry

[Ken H.]

Don't press it in. Heat the wheel hub enough to drop it in.

[ShovelStrokeEd]

Beware of too tight a fit when sleeving the bore of a bearing. You will wind up taking up the internal clearance in the bearing necessary to maintain oil/grease film. On a 25mm hole, you should probably not go tighter than 0.001". This depends, of course, on the fit of the outer race in the hub. If that requires heating or a press fit, the fit of the inner should be a sliding fit. A look in the Machinests Handbook or in the bearing mfg's catalog should give you the proper fits. You violate them at your peril.

[MCDenny]

If its the ID you are concerned with you will need to freeze the insert, not heat the hub. You can press in the insert to the new bearing by carefully supporting the bearing on its inner ring only. That way the pressing force will go from the insert to the inner ring to the workbench and not go through the balls.

 

A good support tool is the inner ring of the old bearing if you can get it apart. To do that you pop out the seals with an awl, remove the cage separating the balls (if its plastic it will pop off, riveted metal will have to have the rivet heads ground off and punched out). Then push the balls together on one side and pinch the rings together on the other side. Last step is finding all those little steel balls on the floor before you slip on one.

 

You can use the old outer ring as an insertion tool to get the new bearing into the wheel. If the tool has to go into the hub too grind or sand a few thousandths off the OD of the old outer ring. Note the rings are rockwell C64 and can't be filed.

 

Probably more than you wanted to know, eh?

[No_Twilight]

Thanks. I'm afraid I've made a mountain of a molehill here. My real concern is that the 3205 bearing is actually a 25mm ID bearing and the one on the front axle of our motorcycles has a sleeve in it. Does BMW supply the bearing with a sleeve in it or do I have to make one. I've about decided this is a non-issue since I can buy the bearing for about $25 savings from Johnson bearing and make my own sleeve. I'll make it the same ID as the 6204 bearing which I believe is very close to 20.00 mm.

 

Thanks,

jerry

[Art..]

I have a 3205 in my hand and it is a 25mm ID.

 

I believe that the sleeve is #8 on the diagram below, BMW part # 36312312285 - "Bush Left". It is a flanged bushing.

 

I could measure it if you like. It costs about $7 from MAX. It appears to be a light interference fit.

 

 

 

Also note that you need #6 - "Pipe" #36312312485.

[ShovelStrokeEd]

BMW doesn't supply the sleeve with the bearing. The sleeve is already there on your bike and should be a sliding fit in the bore. You should be able to push it out with your thumbs. The sleeve not only adapts the 25mm bore to the 20mm axle but also provides spacing, along with the inner 'pipe' to keep the compression load from tightening the axle nut from placing any load on the inner races. You should stay with the assembly as designed from the factory using the 3205 bearing.

[No_Twilight]

Nice drawing Art, thanks. Also very interesting that the pipe shows a spacer on both ends but the disassembly procedures always tell you to push the pipe aside and drive out the bearing...not gonna happen with it well centered on both ends. And both wheels that I took apart had a spacer on both ends just like shown. I made an expansion mandrel go go inside the innner race for "tapping".

 

So Ed, I agree with you that this bushing should be a looser fit but BMW seems to be pressing it in. I can't imagine that local shops are set to do this. Anyway, I can press the one out of the old bearing and reuse it or I can make my own with a lubricated fit. Haven't decided which to do yet. Now I've got all the info.

 

I've got the pipe that came out of one of the other wheels ready to go back in.

 

Thanks,

Jerry

[ShovelStrokeEd]

It is likely corroded. Every wheel I have ever taken apart has that center spacer captured between the bearings, it's a function of the squeeze they get from the axle nut. A little adventure with a long punch to pry it to the side will allow it to get out of the way.

 

When you do get things apart, just lightly sand the sleeve until it's a sliding fit in the new bearing and you'll be good to go. I have had my front wheels off numerous times on my various BMW's and the spacer has always come out with just my fingers pulling on it or with a light tap, once the 'pipe' is moved from a long punch on the other side.

[Art..]

Also very interesting that the pipe shows a spacer on both ends but the disassembly procedures always tell you to push the pipe aside and drive out the bearing...not gonna happen with it well centered on both ends.

 

 

I've got the pipe that came out of one of the other wheels ready to go back in.

 

Thanks,

Jerry

 

Yeah, I know what you mean.

 

The new pipe that I have in my hand isn't actually flanged, it has two thin spacer rings pressed on that look like they're made of spring steel. These appear to be merely there for locating purposes.

 

I have looked at the bushing again this morning. I don't have my good mic with me, but I cleaned it up with 150 (it's a new bushing and a new bearing) and it still appears to be light interference (sorry to contradict you Ed - not trying to cause confusion ) It is possible that I have a bad bushing................

[Art..]

The sleeve not only adapts the 25mm bore to the 20mm axle but also provides spacing, along with the inner 'pipe' to keep the compression load from tightening the axle nut from placing any load on the inner races.

 

Not on mine it doesn't. The bushing, from inside the flange to the end of the bushing, is 19mm. The bearing is 20mm wide.

 

Which means that the flange pushes the inner race, which solely pushes the pipe.

 

Maybe we're seeing a revision here. Maybe BMW originally supplied these with sliding fit, and then spun a few inner races that weren't torqued down properly.

[ShovelStrokeEd]

Another point here, the inner spacer, the one that goes inside the wheel between the bearings and bears on the inner race, may well be wheel specific. It is vitally important to the life of the bearings that the length of this spacer be slightly longer than the distance between the internal flanges of the wheel into which the outer races of the bearins seat. If it is too short, you will place a side load on the bearings when you tighten the axle nut and they will quickly fail. I have seen this happen a couple of times on a stock wheel, maybe Hans had a bad day.

[No_Twilight]

Art, since you have all the parts in your hand, does that mean you're getting ready to put a wheel together? If so, what did you and do you plan to heat the hub with? I know it would be easier with a hotter hub but I don't want to burn the paint off with a torch. I used an industrial strength hair dryer that puts out 500 degree air but Al is such a good conductor of heat that you almost have to heat the entire wheel. Freezing the bearing is very important to.

 

--Jerry

[Art..]

I have an adjustable heat gun.

[Art..]

Another point here, the inner spacer, the one that goes inside the wheel between the bearings and bears on the inner race, may well be wheel specific. It is vitally important to the life of the bearings that the length of this spacer be slightly longer than the distance between the internal flanges of the wheel into which the outer races of the bearins seat. If it is too short, you will place a side load on the bearings when you tighten the axle nut and they will quickly fail. I have seen this happen a couple of times on a stock wheel, maybe Hans had a bad day.

 

Good point.

 

I have a new pipe here, part # 36312312485.

 

For reference, it measures 2.29" (58mm)on my cheapo dial caliper.

 

This is for a 3 spoke, 1997 spec wheel.

[No_Twilight]

I have a new pipe here, part # 36312312485.

 

For reference, it measures 2.29" (58mm)on my cheapo dial caliper.

 

This is for a 3 spoke, 1997 spec wheel.

 

I just measured mine with a calibrated micrometer and got 2.285". 58mm is 2.2835 which I think is close enough to conclude that is the spec. However, a quick and dirty measure of the distance between the bearing lands in the wheels is 2.268" so I have to do a little work to figure out the difference here.

 

--Jerry