BMW Airhead Gearbox Removal

The BMW Boxer gearbox can be removed as a separate unit without the need to remove the engine from the frame.

The process shown here removes as little as possible from the bike to make a gearbox swap as quick as possible.









The gearbox is held to the engine by just four bolts. However to lift the gearbox free from the clutch splines it is necessary to move the swinging arm back and remove the battery. It is also necessary to disconnect the drive shaft, speedo cable and clutch cable, and the airbox has to be removed.









Loosening drive shaft bolts.

To start, the bike was secured on the centre stand and the gearbox and drive shaft oils were drained.

After peeling back the drive shaft gaiter, the four drive shaft bolts were undone by holding the back wheel on the brake and undoing each bolt in turn. The bolts have twelve faces rather than the usual six and so a 10mm ring spanner is the best tool for the job.

These bolts are stretch bolts and so should be replaced during re-assembly.









Next the rear wheel arch with light assembly was removed, the speedo and clutch cable disconnected. The brake pedal assembly was also removed........









..... followed by the swinging arm bolts.

These were removed using a box spanner to loosen the locking nut and then an Allen key to remove each pivot bolt.

The back wheel was now free to swing backward on the rear shocks and was strapped to the rear of the bike fame out of the way.









The battery was disconnected and removed in its mounting tray by undoing the 4 cushioned mounting nuts









The airbox was removed by first detaching the inlets to the carbs; then working on the left side first, the long clamp bolt was removed, then the air filter element. The clamp bolt on the right released the RHS

Long airbox clamp screw

RHS clamp bolt.









The clutch arm was removed by prising the circlip off and extracting the pivot shaft.

Then the arm, piston and thrust bearing assembly could be lifted out.

Removing clutch arm pivot

Removing clutch arm









The remaining gearbox nuts were removed and the gearbox slid from the clutch splines. The box was removed from the left-hand side of the frame as shown.






Re-assembly notes.

Inspection showed that the clutch actuator rod and thrust washer were badly worn and the felt oil ring was missing.

These parts were replaced.

Worn clutch rod (swashed area).









Fitting a new felt collar was done by first soaking the collar in oil and then placing it on the shaft.

The shaft was re-inserted into the gearbox from the clutch side where an internal chamfer made it much easier than installing from the other end.

Inserting clutch rod with new felt.









Before connecting the drive shaft, the airbox was replaced to run the engine and test the gearbox in situ. With the engine running the clutch was adjusted for correct free play and all gears checked for selection and quiet running.

When connecting the drive shaft the four stretch bolts were tightened to 43Nm with the home made BMW tool.

New oils were added to the gearbox and drive shaft before test riding.

Gearbox = 800cc Hypoid GL-5 SAE 90

Drive shaft = 150cc Hypoid GL-5 SAE 90