Sealed Swing Arm Bearing Question

[Jeff in W.C.]

My 1988 R100 RT has sealed swing arm bearings. I think I know the answer to this, but I thought I'd ask. I had the swing arm bearings replaced about 15,000 miles ago and I didn't expect them to be bad. But, when I checked them, there was a lot of side to side play. That would be a side to side (left/right) with the swing arm on the bike. If you were staring down at the bearing in the swing arm, it would be an in/out or up/down play. I hope I explained this well. I don't there should be any play whatsoever. I really thought the bearings should last more than 15,000 miles, but if they're bad--they're bad.

[gspd]

Those are tapered roller bearings.
They should be cleaned and repacked once in a while.
Free play is adjusted with the pivot pins.
If you have the later 'sealed' type bearings, the 'seal' can be popped out (and re-installed afterwards) to allow inspection, cleaning and repacking.

[Rob Frankham]

Chaecking, lubricating and, if necessary, adjusting the pivot pins on the swing arm is a service task. If they are kept lubricated, adjustment is seldom necessary. If kept adjusted, they will last a very long time. The grease shields are helpful but you still need to grease the bearings regularly. If they've been left unadjusted and unlubricated for 15,000 miles then all bets are off and you need to check them.

Adjust the bearings in the normal way..

1) Loosen the lock nuts
2) torque the central pin to 20 ft lbs
3) Loosen the pin and retighten to the working setting of 11 ft lbs
4) Re tighten the lock nut to 110 ft lbs
5) Make sure the swing arm is central in the frame. If not loosen and try again using the threads on the pinms to adjust the position of the swing arm.

(Special tool alert!... most sockets will not fit the lock nut because they won't fit into the recess in the swing arm. You can get (or make) special 'thin wall' sockets for the purpose. The BMW tool in the toolkit will fit the nut but will be a problem when it comes to setting the torque.)

6) Remove the rear wheel
7) Disconnect the rear suspension unit.
8) Lift and lower the final drive to the limits of it's travel. If there is any change in the resistance to up/down movement or increase in side to side movement, the bearings are 'brinelled' and will need to be replaced.

Comment... If the bearings have been kept lubed and there is substantial side top side movement after only 15,000 miles it suggests that they may not have been fitted properly in the first place...

Rob

[RPGR90s]

What you've described is mis-adjustment of the swing-arm and not necessarily bad bearings. Side to side movement of the swing-arm (installed in the bike) is controlled by the left and right pivot pins, and secured by the pivot pin lock nuts.

Since they are tapered bearings, the pivot pins need to be torqued (typically 7-9 ft. lbs.) with the swing-arm having identical clearance between the frame.

The procedure is listed in several manuals.

[Jeff in W.C.]

Rob/GSPD,
Excuse my lack of knowledge here, but I don't understand how you can clean and re-grease sealed bearings. I've cleaned and re-packed standard tapered bearings. But, with the sealed bearing(s) in the swing arm, I just don't see how that works.

GSPD, if I remove the removable dust seal, you can't see the bearings. Just another smaller black seal just like the one below (the official BMW part from MaxBMW's website).



I do plan on reinstalling the swing arm and check the movement and play as Rob suggested. I won't be able to get to that until later today or tomorrow.

[Kurt in S.A.]

Can you just used the unsealed version of the bearing?

Kurt

[gspd]

GSPD, if I remove the removable dust seal, you can't see the bearings. Just another smaller black seal just like the one below (the official BMW part from MaxBMW's website).

Those seals can be removed from the bearing for cleaning and repacking. Use a dental pick or tiny screwdriver to lever them out.
It's just as easy to re-install them.
If everything is well repacked with grease the seals are sorta optional anyhow.
Press the bearing inwards as hard as you can with your thumb and rotate it. Should feel free and smooth.

[Jeff in W.C.]

FWIW, Boxer2Valve indicates that these sealed bearings do not require any periodic adding of grease and are greased for the life of the bearing since they are sealed. See the following video and go to 7:50 min for his discussion on the bearings.

[gspd]

FWIW, Boxer2Valve indicates that these sealed bearings do not require any periodic adding of grease and are greased for the life of the bearing since they are sealed. See the following video and go to 7:50 min for his discussion on the bearings.

They're only 'sealed for life' until somebody unseals them.
They should not need replacing at 15,000 miles.
They were improperly installed, improperly adjusted, or they're just plain faulty.
I'd 'unseal' them for inspection before deciding if they need to be replaced.

[Rob Frankham]

Rob/GSPD,
Excuse my lack of knowledge here, but I don't understand how you can clean and re-grease sealed bearings. I've cleaned and re-packed standard tapered bearings. But, with the sealed bearing(s) in the swing arm, I just don't see how that works.

GSPD, if I remove the removable dust seal, you can't see the bearings. Just another smaller black seal just like the one below (the official BMW part from MaxBMW's website).



I do plan on reinstalling the swing arm and check the movement and play as Rob suggested. I won't be able to get to that until later today or tomorrow.

The bearings with grease seals aren't the only ones supplied for post '84 machines... they were introduced to reduce maintenance tasks in the shop (and IMO they weren't totally succesful). From what I remember, they only have seals at the front, (i.e. the larger diameter or, in this case, the outside) not at the rear and, assuming i'm right (I have unsealed bearings on my Mono RT) they can be greased in the same way as the earlier bearings... that is by forcing grease down the centre of the bearing pin with a suitable grease gun. To my mind, it is always worth getting grease into even a fully sealed bearing periodically. The action of the bearing itself will tend to push grease away from the bearings themselves and this is particularly true of bearings with limited rotation (like swing arms and steering heads) where grease can be pushed into the area not normally used by the bearing elements.

I have some respect for the B2V videos but I don't always agree with everything they say... in this case, I don't agree that the swing arm bearings are so weak that they have to be replaced every time you take the swing arm out of the frame... examined, yes but not replaced unless there is a problem. Given proper lubrication and adjustment, the taper bearings will last for tens of thopusands of miles.

In this case, the issue is that the bearings are obviously out of adjustment. As GSPD says:

"They were improperly installed, improperly adjusted, or they're just plain faulty."

If they have been out of adjustment for 15,000 miles then there is every possibility that they will have received brinelling type wear (as shown on the B2V video) simply because of movement of the swing arm in use. If that wear is present, the bearings are toast and need to be replaced (again). The rough and ready way to check for excessive wear is as described in my earlier post.

Rob