After I got the engine installed in the frame, it’s time to get the transmission installed. I had refinished the transmission earlier, but did not rebuild it. You can read about these parts of the project here.
I used the following references to plan my work.
- Bob Fleischer: BMW Airhead Clutch Information
- Bob Fleischer: Serving Transmission Input (clutch) Splines, Throwout Bearing, Clutch Arm
- Duane Auscherman: BMW Motorcycle Clutch Removal, Inspection and Repair
I installed the following new parts that I purchased from Hucky’s.
|23 41 1 232 116||Shift Lever Boot, 4 Speed||1|
|21 51 1 230 109||Clutch throw out lever rubber cup/seal||1|
|21 52 1 020 109||Clutch throw out Seal||1|
|23 21 1 230 440||Clutch throw our rod felt ring||1|
|23 21 1 230 106||Clutch thrust rod /5, 4 speed||1|
Install Clutch Throw Out Rod Assembly
The clutch throw out rod assembly has to be installed into the transmission in the housing to the right of the kick start lever.
Below are the throw out lever, pivot pin with cotter pin and return spring on the left. The throw out lever pushes on a piston with rubber gasket in the middle of the piston. The other side of the piston contacts the flat face of the throw out rod. The throw out rod passes through a a circular ball bearing race and it’s outer race. The throw out rod has a felt oil seal that fits in a groove to keep water and dirt from getting into the clutch housing. The throw out rod goes through the center line of the clutch and the tapered end of the rod pushes on the clutch pressure plate to disengage it from the clutch plate.
This is the front face (towards the transmission) of the outer bearing race with the hole for the throw out rod.
This shows the back side of the outer race with the groove that rides on the ball bearings which are shown behind it. The grooved back side of the outer race fits on top of the ball bearings, not the flat front side.
The ball bearing race presses against the piston assembly that has a large gasket ring in the middle and a pin on the other that goes through a rubber boot into the cup on the lever arm. The clutch lever adjuster pushes on the pin of the piston assembly to adjust the clutch free play.
The cup in the clutch lever holds grease to lubricate the piston pin. There is also a zerks grease fitting that is used to lubricate the pin holding the clutch lever on the ears on the back of the transmission.
Install the Felt on the Throw Out RodThe felt for the throw out rod is slit on a diagonal so it fits in the groove on the throw out rod. It is often a bit too large to insert into the transmission and needs to be trimmed. I trimmed a small amount and test fit the throw out rod and continued trimming until it was snug but I could still push and pull it in and out of the transmission Here is how much I removed from the edge of the slit.
Then I oiled the felt with engine oil.
Greasing the Transmission Input Shaft SplinesThe Transmission input splines need to be greased. I use Honda Moly-60 Paste and use a toothbrush to put it on the transmission splines but I don’t overdo it.
CAUTION: Do not put any grease on the internal splines of the clutch plate as it will get throw off and will lubricate the clutch plate. ONLY put grease on the transmission spline.Install Clutch Throw Out Rod In the TransmissionIt is easier to put the rod in from the front of the transmission (the end that mounts to the engine).
I also put a VERY SMALL dab of grease on the point of the throw out rod which presses on the clutch pressure plate.
Install the Transmission Into the FrameI added padded the frame with some sponge matting that was used to warp my powder coated parts so I won’t scratch the frame as I install the transmission.
I pushed the clutch throw rod all the way into the hole in the center of the transmission input shaft spline. I also removed the kick starter for more clearance but didn’t remove the shift lever. I used it to help hold onto the transmission as I carefully guided it into the frame from the left side. I found that tipping it about 45 degrees from the horizontal made it easier to clear the frame members. I put it down inside the frame tipped on the side so I could then get behind the frame and easily pick it up and hang it on the upper left stud.
Transmission Mounting HardwareThe left side of the transmission mounts with two Allen head cap screws that go into tapped holes in the engine. One bolt has a polished head and goes on the bottom. The other with the knurling on the head goes on top and holds the left side air box cover on. It goes through a metal tab and a thick spacer to offset the tab from the engine case.The right side mounts to a stud on the top left of the engine with a nut and on the bottom it mounts with a long Allen head cap screw that goes through a hole in the engine casing and the transmission.
I aligned the splines by spinning the transmission input shaft a small amount until the transmission slide into the clutch carrier splines.
Then, I slide the transmission firmly into the back of the engine case and put a nut and wave washer, finger tight, on the upper right stud to hold it in place.
I added the lower left bolt and wave washer, then the bottom right bolt leaving the top left bolt with the thick spacer and metal tab for last, again finger tight.
Finally, I assembled the upper left bolt, bracket and spacer finger tight and test fit the left air box cover to ensure it would fit correctly. The edge of the cover slides between the transmission housing and the metal tab and under the bottom of the transmission bolt.
Install Throw Out Rod Bearing AssemblyThe throw out rod is visible from the rear of the transmission. The throw out rod bearing assembly goes over the throw out rod inside the throw out bearing housing.
The bearing stack is inserted, as shown below, with the outer bearing plate with the hole in it going in first, followed by the circular bearing race and then the piston with rubber gasket last. I lubricated the bearings before installing the assembly.
When the bearing assembly is installed the pin on the end of the piston extends between the ears that hold the clutch lever.
Attach the Clutch Lever AssemblyThe clutch lever has a rubber cup installed as shown below. Note, the rod at an angle extending from the cup is really a screw driver on the floor and not a part of the throw out lever 🙂
The pin on the end of the piston assembly goes through the hole in the rubber cub when the clutch lever is inserted between the mounting ears.
The clutch lever is secured with a pin that is pressed through the holes in the mounting ears on the transmission and secured with a cotter pin. There are two grooves in the pin. It is inserted until the outside groove is flush with the outside of the mounting ear.
The cotter pin slides into the holes in one of the mounting ears and passes through the first groove in the pin securing it in the mounting ears.
Finally, the return spring is installed on the pin on the clutch lever and the pin on the outside of the transmission housing.
Torque the Transmission Bolts & Install Kick Start LeverWith everything assembled, I torqued the transmission bolts to 17 FOOT/pounds.
I checked again to be sure the left side air box cover slides behind the top left metal tab.
Install Kick Start LeverI installed the kick start lever with the beveled pin and torqued the nut to 15 FOOT/Pounds.
Here is the transmission installed in the frame.