Converting 2-stroke motors to steam

[hartleymartin]

I've come across some YouTube videos showing the conversion of 2-stroke "Weed-Whacker" motors into single-acting steam engines. Does this actually work for steam-boating purposes?

What I find most interesting is the use of a check-valve where a rod inside the cylinder comes up and opens the valve to admit steam instead of using an eccentric and other valve gear. This seems rather attractive, as to reverse, one simple needs to close the throttle, spin the flywheel in reverse and then open the throttle again.

I can probably lay my hands on an old 2-stroke motor quite easily. Does this seriously work?

[Mike Rometer]

I presume from what you say that the steam is fed through the spark-plug hole, and exhausts through the crankcase (Exhaust ports blocked off) so that steam oil is carried to the crankcase bearings.

I'd have thought that a semi rotary or poppet valve could be driven from an outside eccentric on the crankshaft, with a simple linkage.

Sounds feasible, but not sure about efficiencies, there could be a problem with the steam left in the cylinder after the inlets close on the up-stroke. but the inlets could be cut further up to minimise that, at the expense of using all power available on the down-stroke.

[hartleymartin]

If it doesn't work out as the main launch engine (on a 16' launch) it can always become a secondary engine using the exhaust steam from the main engine to power auxiliary systems. It's probably one of the cheapest ways to get a working steam engine.

[hartleymartin]

Quite a few conversions seem to make use of a reed switch activated by a magnet on the flywheel in place of a mechanical valve gear, although this person shows some sort of mechanical valve.

https://www.youtube.com/watch?v=M1yqZ4rmvrk

And, of course, it turns out that this isn't an entirely new idea. Small airplanes have been run on very similar CO2 motors for some time, but electric motors are now powerful enough to have made most of these redundant.

http://www.animatedengines.com/co2.html

Presumably, as it exhausts at the bottom of the stroke, drain cocks would not be required and risk of water-lock would be reduced compared to a normal double-acting cylinder.

[Mike Rometer]

Probably still need some sort of drain on the crankcase as the large area would remain comparatively cool.

[hartleymartin]

I suppose the next questions to ask are:

1.) What bore/stroke is needed to make a powerful-enough steam engine?
2.) What sort of steam pressure is needed to operate at 400-500rpm? (this seems to be the speed of most launch engines)
3.) Aside from the valves, are any other modifications necessary for this to work?

[fredrosse]

I have built a small steamboat plant from a 4.7 cubic inch (77cc) chain saw engine. The machine drove a canoe sized steamboat, producing about 1/4 horsepower at 600 RPM with 150 PSI steam.

The low speed of this engine, compared to the thousands of RPM in chain saw service required a heavy flywheel, I used a 6 inch Schedule 80 butt weld pipe cap for a flywheel.

This engine is somewhat more complicated than the typical "Bash Valve" we see on You-tube, having a lube pump which fed the bearings, and a substantial gap between the steam piston and the crosshead, which was the original IC engine piston. A hard chrome cylinder from a pneumatic cylinder replaced the original ported cylinder, and the unit had a conventional piston valve for admission and exhaust.

Engines where the piston pushes open a steam admission valve at the top of stroke (commonly called "Bash Valve" engines), and exhaust thru typical piston uncovered cylinder ports for exhaust are simple enough, but difficulties with lubrication need to be better addressed, and I think this would be necessary if anything is going to last much beyond You-tube video presentations.

I have also made steam engines from four stroke IC engines, and this is a better choice in my view.

[hartleymartin]

I'm wondering if a propellor with a finer pitch would reduce the load on the engine but still give enough speed. It isn't really worth it unless you can get at least 4 or 5 knots. You need to be able to motor against currents and winds!

I would think that a displacement lubricator would take care of lubricating the cylinder and perhaps enclosing the crank-case and running in an oil bath should take care of the big end bearing.

[hartleymartin]

I wonder...

If a large 2-stroke engine was modified, can it work better on lower steam pressure?

The typical small 2-stroke motors are variously 25-30cc, then about 66-80cc and then there are some mower engines about 160cc

[barts]

At some point, a simple overhung crankshaft running in pillow blocks is easier than a conversion....

- Bart