A Bit of a Wobbler
When out on the BMW sidecar outfit at the weekend I noticed a trace of steering wobble that was not there before.
Once back home I checked things over.
First check was tyre pressures, especially the front wheel. These checked out in spec.
Next was steering head bearings, and the front wheel bearings while at it, these were all free and had no play so that was something else crossed off the list.
Next in line came the rear swing fork and wheel bearings. Some play was found in here in both horizontal and vertical planes.
This cleared the swing fork bearings, if these had been at fault the play would have only been found in the horizontal plane, so new rear wheel bearings were indicated.
Thing is that the rear wheel in my combo is an EML unit and NOT a BMW one so the bearings in it are different to those shown in the spares book, and, as I wanted to have the new bearings “in hand” before I started work, I needed to know what they were.
An email to EML themselves failed to receive an answer so I tried the BMW lists on the internet. I received an answer from a member in the States who has an EML outfit with the bearing numbers and I soon managed to get a set from a local bearing specialist.
So, to work!. First thing is to get the bike up onto it’s centre stand. Not as easy as it sounds because the reduced tyre sizes I run have lowered the bike. It’s only by about an inch but the roll-on action of the centre stand no longer works, you need to do a dead weight lift of the bike to get it high enough to lower the stand and it’s b—-y heavy, in fact it needs the use of a jack to remove the risk of a rupture!
Next is that as I am running a non-standard tyre, a wider section car tyre, on my rear wheel the normal BMW quick removal system does not work, the tyre will not clear the brake shoes and drive hub, I have to remove the wheel complete with the rear bevel box and this is not as simple a job as it seems.
First is to disconnect the rear brake rod, next drain the oil from the drive shaft housing, undo the 4 nuts securing the bevel box to the swing arm, remove the lower mounting bolt from the right hand suspension unit. (Oh and it gives more clearance to work if you remove the offside silencer to start with)
Now you can remove the rear wheel spindle and pull the entire assembly back out of the frame, and it’s heavy!!.
Once I had the assembly clear I could lift the wheel away and have a look at the bearings. Sure enough they had been fitted with the bearing numbers facing inwards so I could not read them! Typical!!.
As my rear wheel is literally a car wheel bolted onto the bike hub the next step was to remove the wheel from the hub, just a case of undo the three lug nuts. (The wheel I’m using is from a Citroen car, typical French skimping on an engineering job! Just use 3 lug nuts when everyone else is using either 4 or 5!!).
With the hub clear it was now just a case of using a long drift to punch out the old bearings, heart in mouth moment as I checked the bearing numbers then the relief of finding I had the correct bearings in hand!.
Replacement was simple just thoroughly clean the hubs bearing seats and bore, grease up the new bearings and the spacer and hub bore and fit the new bearings in place, the old bearings make a good pressure bush for this and all that’s left to do is re-assemble everything and find that the wheel is locked solid when I nip up the spindle nut but will turn when I ease the spindle nut!
Guess who forgot the spacer between the hub bearings and the drive?.
On the original BMW hub this is captive, held in place by a separate grease seal between the (open) bearing and the drive. EML widened the gap between the bearings by substituting sealed bearings for the bearing/grease seal pair and using a loose spacer on the spindle instead. An improvement giving a stronger hub for sidecar use BUT!.
This resulted in blue air and a frantic search for the missing spacer!.
Once it had been found and installed, the wheel was now turning easily and I could look to refitting the assembly onto the bike.
Simple way was to put a 4 inch piece of timber down and stand the wheel assembly on that. Doing this brought the bevel box up into near its correct alignment with the rear fork and made it a simple matter to bolt it in place and refit the suspension unit and the rear wheel spindle, not forgetting the rear brake actuator rod.