Restoration of BMW R90S
This is not a restoration blog. Indeed, I have not "restored" the bike. I did not remove the motor from the frame and nearly all the paint is original, the wiring is original and very few parts were replaced. Instead I partly disassembled the bike including the frame, suspension and brakes, in order to detail them carefully and assure myself of the condition of everything. Parts I did routinely replace were those parts made of plastics and rubbers, including cables, grommets, hoses, seals etc. As well I disassembled the carburettors for cleaning and replaced gaskets, o rings, needles and seats and jets. I also paid special attention to the wiring loom. In my experience the only thing that can be relied upon to give trouble on a BMW is the loom. Electrical connections degrade simply because we live in an oxygen atmosphere. On all my bikes I perform a routine annual maintenance routine to break and clean every electrical connection. Afterwards I coat the connectors in vaselene. This page is just a library of photos I took along the way with the "rennovation" of my R90S that may be of interest to restorers of these wonderful old motorcycles
Handle bar clamps
The handle bar clamps were easily restored by first stripping the old finish (using paint stripper). Next, after thoroughly cleaning them, the surface was prepared using 1800 grade wet and dry paper. An etching primer provided an undercoat and after waiting several days for the undercoat to properly cure, numerous coats of two-pack base coat paint (BMW code 086) were applied from a pressure pack preparation. Several days were allowed for it to harden, then the clamps were lightly buffed with 2000 grade wet and dry. I polished the central ribs more heavily to remove the black base coat, taking care to roll over the edges and create the same result as originally produced by the factory. Finally after washing well with Prepsol, 4 coats of clear finish were applied and the painted pieces were buffed with a fine cut polish to a smooth mirror shine.
All instruments were badly weathered. They were removed from the bike and sent to an instrument builder for professional restoration. New instrument cases are now available again, although expensive.
Rear Light Assemblies
I took photos to assist with re-wiring
Swing Arm Assembly
The swingarm was unmounted and repainted. New bearings were fitted and correctly adjusted to the same gap on each side.. As the photo shows there is a very close fit between the arm and the rear tyre. I believe this to be caused by fitment of an incorrect tyre size. The rear tyre should be four inches wide. The rear tyre is 110mm wide. That is approximately 10mm too much. There are two possible solutions: fitment of a 4" tyre or use of a spacer inside the rear hub to move the wheel 10mm to the left of the differential.
Front Forks Assembly
I took photos to assist with re-assembly. A pair of new springs were order from MaxBMW. As can be seen, MaxBMW supplied un unmatched set of springs. Regrettably they have not responded to my requests for replacement. I have six BMWs to restore. I will continue sourcing my parts from other suppliers in future.
When it came to reassembly of the headlight cabling, I was sorry I did not take more photos because there seem to be many varieties of the documented wiring design in these motorbikes. Although the old wiring on this machime is original and unmodified, it is unlike any of the R90S wiring diagrams I have seen.