Well I couldn't find my original thread about engine spacers and a possible solution to a misalignment of my transmission output coupling and the the drive shaft coupling so I'm back with additional information on this odd to me problem.
The bike: 1979 R 100S VIN 6165010, one owner bike complete with extensive service and repair records. No documentation or visual indication of a bent frame or accident. The frame has undamaged factory paint and all components line up and assemble with no need to pry or persuade to install.
The problem: The output flange of the transmission does not line up with the drive shaft flange unless I adjust the swing arm pivots nearly all the way to the left, this leaves the wheel out of whack at the fender and the right side pivot pin almost to its stops. if the swing arm is centered the drive shaft binds in the tube.
Findings so far: All motor spacers are correct and in place as installed at the factory. The output flange of the motorcycles transmission (finned later model case) is located approximately 10mm further to the left in relation to the trans body than output flange on my spare transmission that has a smooth early style case. This is just the way the castings have measured out and is not due to damage or modifications.
Additional information: I had a chance to visually compare the output shaft locations and general clearances of drive shaft couplings and transmission dimensions when mounted on a number of '75-84 airheads and the one in my R 100S is clearly not the same as the others I inspected just last weekend.
I have installed a new larger tube swing arm from a later model RS bike but the stock swing arm and drive shaft assembly had damage consistent with a misaligned swing arm that caused the drive shaft to bind inside the tube.
My questions: Do I have the wrong transmission in my bike? Is there a difference between a mono shock transmission and a dual shock one in regards to the location of the output flange? Does an early GS have a transmission that has the output flange located differently? What about an R 65 transmission, are they different?
My quandary: I'm a /2 guy and somewhat new to airheads, this is an extremely nice and well documented bike and its a keeper and rider but I want it to be correct. I have been told all the airhead transmissions are the same and interchangeable so just what am I missing here?
There may be a reward for the solution to my problem!!!