I mounted the engine in a drill press vice and put the stub of a socket head wrench (about 1") in the drill press chuck. I lowered the spindle and the wrench into the socket head bolt, and added moderate downward pressure. I then slowly turned the chuck by hand just enough to loosen the bolt. (It goes without saying, the switch to the drill press was not turned on.) I found this useful in removing phillips head screws also. To get a good grip on the chuck, I inserted the chuck key for leverage.
Good luck,
Cajuncharley