Next stage get the 1970/80's swing arm to fit a 1959 frame - read angle grinder.....
So the 5 series swingarm was seleceted on a couple of fronts - choices of bevel box ratios and longer wheelbase + it looked like a challenge and the 5S arm would match up the new wheels 19mm wheel spindle plays 17mm spindle. Other considerations -5 inch wide slick tyre and its space requirements within the swingarm both side to side and also front to back around the pivot end. Wheel alignment - would be nice to have both front and back wheels on the sametrack. The swingarm will not be doing any swinging in its new home and the rear of the bike will be a hard tail with rigid struts in place of the plunger shocks.
The first part and main part to sort out was the width of the 5S arm at the pivot point which was around 20mm to wide for the frame, and a side issue from this was the drive shaft center line plays the gearbox drive flange location and getting these to play nicely. With the engine and box in the frame we moved them over to the drive shaft side and put in some washers to take up the small gap between frame and engine inner mounts to help our cause.
After some measuring and marking out we had a plan, first was to remove the drive shaft side pivot bearing then cut down this side tube by around 10mm effectivly moving the drive shaft when viewed from the rear 10mm to the right this bringing the gearbox and drive shaft center lines to almost perfect alingment. The plan is to replace this side bearing with a solid steel bush pressed in place more of this later...
The next step was the gussets that formed part of the design around the pivot tube these needed to be removed to help with clearance the tyre would need - clearly BMW put this gusset in for a reason to strengthen up the arm in this location and the long term plan will be to weld in place a tyre friendly gusset when its all finished but at this stage its get as much room as possible.
So as BMW intended + some grease and dirt.
Final job on was to cut 10mm out of the center of the swing arm this is how it ended up.
Now its in a pile of bits the drive shaft side was offered up with bevel box and wheel hub at this stage very much a jury rig but still we looked to have a almost perfect hub to center line of frame alignment, but with a lot of variables at this stage its just a hopeful light at the tunnel end.
What has also come out is the driveshaft is too short at the gearbox end and we will need to make up a spacer / spider again more on this later.
Mocked up in the frame.
Next stage will be the rebuild, making up various parts and alignment jig so this will be a strong as BMW intended and hopefully it may even fit when were finished.......