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Oscillating Engine

Nigel Taylor

This article starts with the engine having been marked up ready for the valves to be drilled in the main plates, hence the engineers blue.

This engine started when I bought the Warco WM240b and I wanted something substantial to make and the idea of a large rather agricultural oscillating engine popped into my head.

The original intention was that it would be a one piece quarter inch thick steel plate that eveything fixed to, but even the 240b would have not had the necessary swing....or maybe just.


The spring and nut that applies the force to the oscillating cylinder and so keeps it in contact with the main body of the engine that forms the valve chest.

The 2 holes are the steam inlet at the top and the exhaust at the bottom.

This is a double acting engine and so the other pair of inlet and exhaust ports are there, but obscured by the brass nut.


The cylinder was machined from a solid cast iron square section.

The bore is 15mm and the stroke 50mm


The main bearing block was machined from a piece of aluminium with 5 brass bolts fixing it to the main engine backbone.

In the bearing block I fitted two ball races, one of which was a very nice tight fit, the other was there, but not quite. The fall back was some TruLoc 268 - what a saviour.


A simple piece of hex brass machined and drilled to turn it into a T-junction for the steam inlet.

The 5/32" copper tube was soldered in one go to the T-junction and the man body of the engine. I pre-soldered the union that you can see in the image.


As you can see both inlets are the top ports and the bottom ports are the exhaust.


The engine was actually running when this image was taken.

There is some slight inbalance between the valve timing for the two strokes, so maybe some minor fettling of the ports.

Also, the exhaust port could open a little earlier and this would help the engine.


Although this engine is rather crude I did remove some of the mass from the crank pin. I drilled the hole and then turned the pin around to machine the other side. This is always tricky as it is so easy to crush thin walled parts in a 3-jaw chuck or leave score marks when it rotates. I solved this problem by using the ER25 collets in a chuck that was then fitted to the normal 3-jaw.

The big end of the crank is in it′s functional state ate this point, the intention is to machine this to a much neater and lighter size.

I′m not that happy with the housing for the main bearing, made from aluminium, it is again crude and functional and needs some work.




Apologies now as I did not turn off the radio in the workshop when filming the engine running for the first time....

The best part is it runs.

My thoughts are to now make up a turbine that fits between the main plates that form the body of the engine and gear this onto the crank. The turbine will then be driven by the waste exhaust pressure.

Here using a Soba vice along with the swivel base to machine the angled cutouts..

The swivel on the vice allowed me to carefully rotate the part to the correct position and then lock it in position.


Part 2 - a double speed flywheel and some decoration

If you have made a similar engine and would like to share your experience we would love to hear from you - ed.