ok i have found myself that i dont need to block anything.

yes it only spins half a turn. but with a flywheel, and no crankcase
pressure it will return to the top if the air/steam injection is timed.

i have fitted the flywheel and made a timed valve that will get air
or steam in just after TDC. one quick punch of gas. i have also drilled
out a glow plug and just need to work out the plumbing.

after sitting down with this little motor and blowing through a fuel line
into the spark hole ( compressor isnt with me) i reckon it should work.

i appreciate the comments
i will try to search what i can, more info would be great.
cheers again.
monster.