This is the best small steam engine around. It is available as a casting kit from Gary Hadden up in Holly, Michigan who has been making these little engines for years. He has successfully run both steamboats and small steam vehicles with them. This is the 3” bore and 3” stroke engine, double acting.
Before explaining the fine features of this engine that make it the best design around one needs to know what the competition is for small, meaning 5 hp to 20 hp steam engines. Most available casting kits are old fashioned sliding (also known as “D” valve) engines with harmonic drive to the valve train. Much better are piston (also known as “spool” valve) engines. The best are poppet valves. There are other issues that have to do with uni-flow, counter-flow, and clearance volume, and cutoff control.
It would take a book to explain all of the subtleties of steam engine design and what we are doing here is simply making a bald statement of what I have learned.
This engine is double acting uni-flow with a three-dimensional cam, roller cam followers, and poppet valves. The crank system is exposed using the rod frame design and using sealed ball bearings. The crank throws are over-hung with a chain sprocket in the middle of the crankshaft.
In consequence of these design decisions the engine has the greatest potential for thermal efficiency of any other contemporary available steam engine. It is also designed to be fairly low revving and using low pressure steam of about 200 psi. The over-hung crank design is not all that strong and the connecting rods are cast aluminum and so the engine is not designed for heavy high pressure use. Of course it can always be engineered differently with more time and money.
The 90 degree cranks are intrinsically impossible to balance. Therefore above 1,000 rpm there is a lot of shaking. However, this is designed to be self-starting, a very important steam engine feature.
The three-dimensional cam means that by moving the shift lever the engine can run forwards and backwards and be varied from low to high torque at any time.
This is a good place to start for any small backyard or small steamboat or small Locomobile-type of road vehicle. It will put out 10-15 horsepower. The water rate should be close to 10 pounds and should be compared to a Stanley steam car water rate of close to 30 pounds. When pounds of water rate are bandied about by steam people what is meant is the amount of water that needs to be boiler per hour to produce one horsepower. It is a common, although approximate, method of showing thermal efficiency.
Gary also makes a 2” by 2” engine casting kit.