Fudmucker
Grey Hound
I have been researching two aspects of the Airhead gearboxes that have interested (read troubled) me in the past. The first one is the change of pitch angle from 15degrees to 17,5 degrees:
"In March 1982 the tooth profile of the helical gears (input shaft gear and the 5th gear wheels on the intermediate and output shaffts) was changed; these are referred to as the 15° (early) gears and the 17.5° (later) gears. The 17.5° gears are marked with an X, and many people refer to these as X gears.
The first few years of the 17.5° transmissions are particularly susceptible a problem where the shock coupler ears break off the input shaft gear. In March 1985 BMW upgraded the input shaft and gear, eliminating this problem. Here (on the right) is an early 17.5° shaft with broken coupler teeth on the gear. The original part is available as a replacement and is much less likely to fail, or the entire shaft can be upgraded."
Longer top gears are only available in the 17,5degree format, so if you have a G/S with an '81 box, forget it.
I'm still trying to find out if one can identify the changeover from the gearbox serial number...
The second concern is the Circlip issue and resultant bearing failure, particularly on higher power output (1000cc) bikes.
(All the Siebenrock upgraders should read up on this one!)
I found these interesting reading:
https://www.largiader.com/tech/airtrans/
https://www.largiader.com/articles/circlip/
"In March 1982 the tooth profile of the helical gears (input shaft gear and the 5th gear wheels on the intermediate and output shaffts) was changed; these are referred to as the 15° (early) gears and the 17.5° (later) gears. The 17.5° gears are marked with an X, and many people refer to these as X gears.
The first few years of the 17.5° transmissions are particularly susceptible a problem where the shock coupler ears break off the input shaft gear. In March 1985 BMW upgraded the input shaft and gear, eliminating this problem. Here (on the right) is an early 17.5° shaft with broken coupler teeth on the gear. The original part is available as a replacement and is much less likely to fail, or the entire shaft can be upgraded."
Longer top gears are only available in the 17,5degree format, so if you have a G/S with an '81 box, forget it.
I'm still trying to find out if one can identify the changeover from the gearbox serial number...
The second concern is the Circlip issue and resultant bearing failure, particularly on higher power output (1000cc) bikes.
(All the Siebenrock upgraders should read up on this one!)
I found these interesting reading:
https://www.largiader.com/tech/airtrans/
https://www.largiader.com/articles/circlip/
