Before going any further, I need a proof of concept.
Went into the local lawnmower repair shop and got an old 4 stroke Briggs & Stratton lawnmower motor (donated).
Now all I need is a piece of 2 to 3 inch pipe to use as the steam generation vessel.
I have an old VW Bug brake master cyllender I can use as the water injector.
The steam generator can be screwed into the spark plug hole.
I'll have to make up some sort of cam on the putput shaft to operate the water injector.
Another cam can open both existing inlet and exhaust valves so that they operate as the exhaust port.
May need a heavier fly wheel (the alluminium one wont be worth much)
Bodge up a frame to mount everything on, suspend it over the barbeque and see what happens.
I see a busy week-end ahead!
PS. Just got off the phone to a pal with an aluminium foundry who has a contact with a cast iron foundry about 3 miles from where I live (didnt even know it existed!). The cast iron guy says casting will not be a problem.
Looks like I may have a nice Christmas present for Nyrenere (my Malawian friend)