Fellow Airheads that have done this conversion (a 1983 5-speed to a 1971 4-speed ) of swapping early and late transmissions, any tips, tricks, problems or ingenuity that you have come across from swapping transmissions. Before anybody asks why I'm doing this...I don't let any handicaps keep my face out of the wind. When I kept falling over with a bad leg, attached a sidecar, solved that problem. When I had a hard time (arthritis) pulling hand clutch, fabricated a foot clutch and hand shift. Now I'd like to install a kick starter (for emergencies). Any advice would be greatly appreciated. :blink: 🙂
No information on gearboxes, but lots of encouragement to keep on riding !
😉
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
If your 1983, R100 has the heavy fly wheel, it will work, but you will have to deal with the shifter being fitted to a splined shaft that emerges from the transmission as opposed to the shift mechanism your bike came with originally.
If your R100 has the later style clutch carrier, you will run into potential trouble with the input shaft and the clutch driven plate because the distance that the input shaft protrudes from the front of the transmission is not the same. This leads to trouble with the clutch push rod length and action.
As a general rule, smooth sided transmissions and ribbed sided transmissions do not interchange . I know for sure that a ribbed transmission will not work in a bike that originally came with a smooth sided transmission because of the clutch release issue described earlier.
Any transmission will bolt up to any motor. It's the flywheel/clutch set up that will give you trouble. You will definitely want to have the clutch push rod from the 4 speed, and one from a smooth sided 5 speed on hand in case there is trouble with the actuation related to the spring diaphragm inside the clutch assembly.
There is a lot of "funny stuff" going on related to the engineering change from flywheel to clutch carrier. Your best bet would be to locate a GS transmission with a kick starter from a same year bike.
Also, with respect to gear ratios, 4th gear on a 5 speed is between 3rd and 4th gear on a 4 speed. High gear on both transmissions are the same. 4th gear on a 5 speed is only slightly lower that 5th. I would think that would be more desirable with a side car.
former Airmarshal, IL.
The 71 has a heavy flywheel, with a 8 tooth starter. The 81 uses a clutch carrier with a 9 tooth. The input shaft on the 71 is longer than the 83. The flywheel may or may not bolt up the the 83 crank. Flywheel bolt changed sizes somewhere along the way.
With a hack, you can carry a complete set of every BMW tool ever made-well almost. Carrying a jump box to start the engine in case of a dead battery would be far easier than converting to earlier gear box. Also can you kick start with the bad leg?
Before making a decision on this project I would ask on the airlist. A similar discussion was on another forum with an airhead section. Snowbum is a good source of information on differences between the years.
This information is based on reading forums, Snowbum and service manual not on personal experience.
Best of luck with your continuing to ride whatever route you take.
Bob
Thanks JAMES for your wisdom, greatly helpful......Sam
Thanks BOB for your knowledge and incite......Sam
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