I gritblasted the crankcases to get a uniform
finish and then glassbeaded it and covered the outside surfaces
in 2-components clear. Took a lot of time to very thoroughly
clean the cases before reassembling. Apart from the obvious
compressed air a good idea is to put the whole thing in warm
water with dishwashing soap to soak loose the grit and glassbeads
in the hard to reach places. And then more compressed air!
I assembled the engine on the kitchen table, BMW engines are
very easy to work on.