When you remove your flywheel for such as to replace a mainseal, etc., it is CRITICAL that the crankshaft be BLOCKED from moving forward. This blocking is usually done by some sort of makeshift tool that places a bit of pressure against the alternator rotor center bolt. This can be done in many ways, from a piece of lumber such as a 2 x 4, bungeed to the cylinders and with a screw to press against the rotor bolt. A small easy to make tool can be made of a piece of allen wrench with a welded or brazed fender washer on one end, over-all about 3/4 inch. The outer cover holds it in place with a slight amount of pressure. A picture of this sort of small tool and a description of it and its use is on Snowbum's website, at  www.bmwmotorcycletech.info

If you do NOT block the crankshaft, you run the risk of the crankshaft moving forward a small amount... probably it could possibly move a bit under 1/4", and the HIDDEN thrust washer COULD move off its pegs. If that happens, the washer will not align back on those pegs as you tighten the flywheel bolts, and you run the risk of MAJOR DAMAGE to the thrust washer....even the engine casting. You will find that the crankshaft will essentially nearly freeze up as you tighten those bolts. You REALLY do NOT want that happening. If you forgot or did not know about blocking the crankshaft, and you want to know IF the crankshaft has moved, this sketch of Tom's will give you the information. The dimensions need to be as shown, in order to know that the crankshaft has not moved. The only way to see and get (however slightly) onto the hidden thrust washer, if it has moved off the pegs, is via removal of the right cylinder.....or disassembling the engine!

Snowbum

http://bmwmotorcycletech.info