Boxerworks.com

On this Mono rebuild I have fitted K75S forks, R100R wheel using my Mono discs and BMW 32/34mm 4 pot calipers I think from a R850(not sure as I bought them a long time ago).
With the old Mono's 14mm master cylinder (I came off a few times after locking up that front wheel!) the lever went back to the handlebar so I put a 16mm one from my '81rt on and the lever does nothing till it's halfway in but doesn't quite get back to the handlebar - so I think I may need a bigger master cylinder.
I am a little confused to how big I should go as according to the MAX BMW parts fiche the R850 uses a 20mm one, The early K1200 that use the 32/34 calipers uses a 16mm one and the Mystic 15mm whilst the R100R uses a 13mm one.
Can anyone shed any light on this for me?

Mucking about today after trying a vacum bleeder to ensure all the air was out I placed a 2.5mm spacer between the brake lever contact point and the master cylinders piston - and hey presto - all seems to work.
So can anyone foresee a problem with building up the brake lever with weld?

According to what I have read he R100R used a 12 mm MC with four 48 mm pistons, and Guzzi used an 11mm with the same setup, and no one ever complained about excess movement, so I would concentrate on the the lever.
Not all levers are the same, some have a longer nose on them and will contact the piston sooner, but I have no idea which bikes they come from.
My 75/7 has been converted to twin disks, and a 11mm sleeved handlebar MC and to get the movement I prefer I drilled and tapped the nose of the lever and inserted a adjusting screw to control the movement. There was already a similar hole in the perch to control the lever position to suit my stubby fingers.
As far as I know the problem with welding aluminum is that all aluminum is heat treated ( T6 or whatever) to give it its strength and it doesnt take much heat to remove this temper and weaken the it . So yes, probably no problem welding it, but how much will it weaken it - who knows,? Most critical items like brakes have a decent sort of factor of safety built in and it will probably still be safe, but the choice is yours.