Another method that I've heard of is to feed a length of cord (starter rope for a lawnmower engine is the right size) in through the spark plug hole, then turn the engine by hand untill it becomes difficult to turn. The idea being to use enough cord to allow the piston to pack it in against the valves. It's cheaper than buying an air compressor, and has an added advantage in that the cord will not suddenly force the piston to the bottom of its stroke, as air will do if you're off TDC by a few degrees.

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1989 300 SEL that mostly works, but needs TLC