I came across this recently and thought it may be of some intrest to members, they are selling units for $1500 USD

2 cylinder, 10 hp engines

Specs:
Each engine weighs about 25 lbs.; dimensions, with the drive shaft, are 21”L x 8”H x 13”W. Materials are brass, aluminum and stainless steel to prevent corrosion. The engine may be installed in any position and uses approximately 22 cubic inches of steam per revolution. It yields about 10 hp from 100 psi of steam at 300 rpm’s. Optimal operating range is from 200 to 600 rpm and 60 to 150 psi.
Operation:
For the full 10 hp from this engine, we recommend using a boiler in the range of 2.5 to 5 boiler horsepower capable of producing 100 psi to power this engine. Lower pressures may be used for applications requiring less horsepower. Speed is controlled by a simple ball valve.



[www.greensteamengine.com]:


regards,
Dave Hume
locosurrey

hi,
these sound like they'd be perfect for my pick up.
Do you have anymore info?
cheers
JB

I've attempted to build one from plans for a friend and I hated it. The plans comprise mostly pictures with photo shopped dimensions. The dimensions don't add up which results in a lot of rework.
The claims scattered round the internet are farcical and or meaningless. 23% efficency, being tested by the United States military, three factories in China, up to 500hp units etc etc.
The plans built units rely on a soldered compression olives hand filed to a ball shape used as a swivel. The pistons are thin and rely on an o-ring to seal which unless slathered in rubber grease sticks in the bore. There is no provision for lubricating the cross head guide. The cylinders are uninsulated. The rotary valve has convoluted passages and miserable valve events with no way of adjusting cutoff.
The so called flex rod innovation is unnecessary as if built geometrically correctly a single universal joint would be sufficient and the latest CNC machined engines have in fact abandoned the flex rod.
Any product like the Green steam engine that is advertised looking for investors or area franchises automatically pushes my "hello hello hello what's all this then meter" up to maximum worry reading.

I doubt anyone has achieved anything other than fractional hp out of the two cylinder unit.