Regular inspection and lubrication of the BMW Airhead input shaft splines is essential for reducing wear on the splines but it also makes a huge difference when it comes to everyday shifting. It’s hard to get a BMW gearbox to ‘snick’ into gear at the best of times, but keeping the spines lubed sure goes a long way to reduce the ‘character’ of these motorcycles. Every little bit counts.
In this quick series you will see how to easily inspect and lube the input splines without being overly invasive. With this method there is no need to remove the driveshaft bolts, so the terror and uncertainty of that operation is taken out of the equation. The swing arm still has to be disconnected from the frame, but that is easy and fairly fool proof overall.
Of course the best method for gearbox and clutch actuation inspection etc. is to remove it entirely from the bike, but we don’t always have time for that nor is that always really needed. Maybe you already know the gearbox is fine because you just had it rebuilt two seasons ago and all you want to do now is lube to splines. The method below describes this quick, intermediate spline service. Note you’ll need a torque wrench good for 110 Nm during reassembly, so don’t rip into this until you have one.
Remove all the usual stuff for working on the business end of an Airhead: The tank, the seat, side covers.
Remove the carburetors.
Remove the airbox, the battery tray, and the speedometer cable as shown by the red arrows.
Disconnect the shock absorber(s). Make sure the rear wheel is supported so you do’t hyper-extend the driveshaft.
Remove the rear brake wing nut so the rod can be withdrawn from the brake lever. On disc brake models you need to remove the brake pedal with master cylinder. Just remove the mounting bolt so the pedal can move a bit when it is time. No need to remove or disconnect any brake hoses.
Remove the bolt from the clutch actuator so when the gearbox is pushed back there is some ‘give’ when it hits the frame. Every little bit counts here.
Disconnect the shift linkage.
Remove the swing arm pivots. Note that you need a torque wrench capable of 110 Nm to get this back together correctly, so if you don’t have one, turn back now.
Now you can remove the two lower gearbox bolts. Remember the right side is a bolt and a nut (13mm) so you will need a wrench over there. The left side is an allen key affair. The bolts shouldn’t be stupid tight, but be careful not to strip the drive head on the allen bolt. The tool seats pretty shallow. Make sure your rear wheel is still blocked and gently pull back on either the rear wheel rim, the swing arm, or the gearbox itself. The gearbox should move about an inch, allowing you enough room to see the splines.
The splines revealed. These look good, but do need some lube.
From the other side…
Using a long-handled artist brush THAT DOESN’T SHED BRISTLES, you can reach into the crack and carefully paint the splines with lubricant. Remember this is not regular wheel bearing grease here. You need the special stuff. You don’t need to load the brush heavily. Just enough to paint a film onto the splines.
Here you can see the brush gently and slowly and carefully painting lube onto the splines. You DO NOT want to drop a load of grease into the clutch, so go slow and use a little bit of grease at a time. Go all the way around and rotate the shaft if needed.
From here you can push the gearbox back into place and start the reassembly process. Don’t forget you’ll need to re-center the swing arm and torque the bearings, etc.