Don't know if they are still in business but may be worth a try.
Saturated Steam. P.O. Box 4175 Miami Lakes, Florida 33014. 800-749-7832, Tangye No. 2 steam engine casting kit.
Or this thread may help...
When I looked at the title of your post the first thing that entered my mind was this, :confused: didn't think about the steam engine which you have a good collection
When I built my Wyvern gas engine I had a similar problem, I did a similar repair as the one Jason suggested but instead of Loctite I used JB Weld smeared on the threads the repair was a success.
Mike.
Peter.
Have a look at this link Stuart Twin Oscillator - Stuart Models | Steam Engines | Model Engineering ... not cheap but a nice engine suitable for a boat of the size you have in mind.
Mike1
Hi Steamchick,
Nice to hear the article brought back memories for you, it also explained for me why the case of a very old brass barometer we have, also has small cracks.
Mike1
I don't think the plans are a free down load, however there is a PDF available of the the original article of the engine build which will give you the size of the model and description Link
Mike1
One engine that you may be able to adapt for your project, is the Centaur gas engine there are plans and castings available for this engine in the UK see link.
Link
Mike1
Hi K2, The engine is blowing back all the time as it has no exhaust valve, basically the flame size and it's position has to be adjusted so the blow back doesn't blow the flame out.
Mike 1