Building A Steam Engine From A Lawn Mower

Enlarge Image Image Gallery Convert a lawn mower engine to steam with this low-cost project. Courtesy of Fotolia/Eva Schinschke

Several years ago I decided to make a steam engine that could be made with simple tools. I thought I'd send it in so if someone else wanted a low dollar steam engine they could try my suggestions.

All you need is a 4-cycle lawn mower engine. It doesn't have to run — just be free — , a grinder, and someone with a welder (preferably wire feed). I got mine from the city dump one Sunday when no one was around.

The engine had low compression because of bad rings, but beggars can't be choosers, so I used it anyway. If you decide to make one, try to find an engine with good compression. I later found out that with bad rings the engine would run fine but the steam would slip past the rings and condense in the crankcase and push the oil out.

The carburetor and ignition can be removed and I took a chisel and cut the fins off the cylinder to help cut down on condensation. The spark plug stays to plug the hole and it would be a good idea to leave the recoil start or install a rope start pulley because when the intake valve opens it's running and it doesn't care what's in the way when it starts.

When I made mine I left the blade on, which I don't recommend, but I wanted to compare it to a gas job. So one day when Mom wasn't home to say 'no', I borrowed a garden hose for a steam line and tried it out. It seemed to work as good as a gas job plenty of power until the hose popped. It's amazing how fast neighbor kids can leave if they think there's going to be trouble!

The first thing to do is to take the camshaft out and have someone weld two lobes 180 degrees opposite the originals (figures A and B in the Image Gallery, figure A being the original cams). Now take the head off and decide which port is going to be the intake. The exhaust is usually threaded so it might be best to use that. I tapped the intake on mine but it doesn't matter.

Once you've decided which port to use decide whether you want it to run clockwise or counter clockwise and turn the engine in that direction until the piston comes up to about 1/8-inch before the top of the stroke. Now replace the camshaft with the original cam for your intake valve so it just starts to open the valve. If it doesn't drop in you may have to grind a little off the cam. The intake should close one thirde to halfway down.