Converting a Lawnmower Engine To Run on Compressed Air

Our most likely exposure to a steam engine these days will probably come courtesy of a railway locomotive. A machine capable of immense power and probably with significant complexity and engineering  in its construction, something the majority of us will only ever be able to see at second-hand. But there was a period when steam engines were much more accessible, before internal combustion engines and electric motors took on the task of automating hard work you would have found small stationary steam engines in all corners of industry.

These engines are on a scale much more easily embraced by hackers and makers, and though vintage stationary engines are thin on the ground these days there are a significant number of people pursuing their construction by converting modern petrol and diesel engines to a more old-fashioned medium.

[Lindsay Wilson] has a lawnmower engine which a few years ago he converted with the addition of a sleeve valve to run on compressed air. It’s not a steam engine because creating a safe and legal steam boiler is an expensive process, but despite this it amounts to the same thing. The engine in question is a small sidevalve single cylinder Suffolk Punch lawnmower engine from which he has removed and blocked the valve gear, and added a sleeve valve powered by a linkage from the crankshaft and using the spark plug hole as an inlet and outlet. He provides a lot of detail on the sleeve valve’s construction, and it really is a surprisingly simple arrangement. We might look for a harder metal than copper pipe for the guide in which it runs though.

The video below the break shows the engine being run up after a period of storage. It’s an effective device, easily capable of taking more air than his compressor can supply.

We’ve featured [Lindsay]’s work here quite a few times, recently with laser wire stripping and modifying a switch mode power supply. And this isn’t the first internal combustion engine we’ve seen converted, we’ve seen a 2-stroke strimmer engine and a rather scary lawnmower with a gas bottle boiler in the past.

24 thoughts on “Converting a Lawnmower Engine To Run on Compressed Air

    1. I think it is the water in the compressed air source (he is not using a dryer in the line), so when the compressed air escapes it cools rapidly and condenses into vapor droplets.

    2. When the pressure of the compressed air drops as it is exhausted from the engine, the temperature of the air drops drops, and goes below the dewpoint of the water vapor in the air, so it forms a cloud and becomes visible.

    3. sure. The air compressor compresses the air from the shop, which contains a level of humidity. That moisture is still in the air tank . When the air is released through the motor, it tends to cool off enough to cause that moisture to condense out into droplets.

    1. only if you look from the p.o.v. of efficiency.

      Examining it from a tinkerers p.o.v. it’s “cheap” as long as the energy to power the compressor is availiable at excess.

      – Used high power machinery, compressors, storage tanks on ebay.

  1. Thanks for featuring this! I keep getting sporadic inquiries about it, so it must be of interest to someone ;-)

    I’ve actually got a half-finished Solidworks model of this, which I was going to turn into a little animation to show the mechanism (and the valve timing) a bit more clearly. Need to get that finished now….

  2. If you happen to live on land that has a creek or river with plenty of drop, you could build a trompe to get huge amounts of free, dry, cool, compressed air.

    The basics of a trompe are simple. A vertical inlet pipe which has several angled pipes piercing its sides. A horizontal section with a raised area in the middle to hold compressed air. A vertical outlet pipe, somewhat lower than the inlet. A blowoff pipe that leads from the air chamber to beneath the water surface at the top of the outlet. The end of the blowoff pipe in the air chamber should be just below the minimum water level.

    How it works. Water flowing into the inlet draws lots of air through the angled pipes. The air is released into the air chamber where it can be tapped from the top. If allowed to build pressure, the water level will be pushed below the end of the blowoff pipe then push through it. It’ll send a geyser of air and water out of the water outlet.

    Simple construction, no moving parts and unlike a mechanical compressor the squeezed air is cool and dry. The coolness is from the water carrying away heat, but I haven’t found an explanation for why it’s dry when there’s all the water involved.

      1. and germans used it in ww2 as a way to produce supersonic air for an aerodynamic testchamber. i don’t know if there were many of these build,but i know one thats about 100 miles from me. have to visit in one day

  3. Well done conversion. Avoided the usual trap of trying to use the existing valvegear. About the only thing I would have done differently was to put the piston valve vertically and avoided the bellcrank. Its easier to get the air to turn a corner than mechanical motion. (but admittedly looks cooler with the linkage turning the corner)

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