Warning! Warning!! WARNING!!!
Under no circumstance should the flywheel or clutch carrier on any model be removed without first blocking the crankshaft from moving forward!! http://bmwmotorcycletech.info/flywheelremovalwarning.htm
You must block the crankshaft! Do not take a chance on serious damage to the engine!
Many have removed & replaced an Airhead flywheel or clutch carrier without blocking the crankshaft with no problems. My advice, very strongly given here, is to take a minor amount of time & make & use at least my simple crankshaft blocking tool. If you do not use some sort of crankshaft blocking tool, & your crankshaft should happen to move forward enough (does not take much pressure nor does it have to move far!) to have one or both of the thrust washers fall off their pins, you could cause very serious damage as you attach & bolt-up the flywheel or clutch carrier. Even if you do not cause serious damage, if the forward thrust washer drops, you may be unable to get it back on its pins without a very considerable amount of work. Do not take a chance!
Since it is a must, in my opinion, to mechanically block the crankshaft from moving forward at any time during the process of removing or replacing a flywheel (or clutch carrier as it is called on 1981+ including some 1980 models), you need to know how to best do that.
This can be done in several ways. I recommend you do not use ‘a towel’ between the front cover & the alternator rotor, as is sometimes done. I recommend a simple & neat method …just make a tool out of a piece of Allen wrench material, weld a disc (fender washer) on one end, making the length such that the Allen end fits into the alternator bolt, & the disc end presses against the inside of the outer timing chest cover. Usually 3/4 inch overall. The length should be such that there will be some light pressure applied by the cover to the tool, the cover being screwed back towards the engine lightly (but not touching the engine case). The tool should be just long enough that the cover can not be fit fully home all the way. Obviously you don’t want to tighten the outer cover very much & you do not need to!
A further treatment of how to make this tool, & a photo of it, is in http://bmwmotorcycletech.info/tools.htm , as item #8A. Note that making the tool requires a very small amount of welding. If you do not have a welder, or do not wish to have the tool made that way, you can just use a piece of allen wrench. The tools article also has photos of the clutch disassembly & assembly tools …you may need three if you have an early model; although three common bolts work well.
At this point I strongly suggest you go look at: http://bmwmotorcycletech.info/flywheelremovalwarning.htm
Whatever tool you use, be sure it cannot rotate such as to loosen its pressure on the inside of the outer cover if you rotate the flywheel in either direction. The advantage of my tool is that it is unlikely to allow the alternator bolt to loosen if the tool is made and installed correctly, as you rotate the flywheel. Be sure the tool is not ‘captured’ by raised grooves on the inside of the cover, etc. Think!