Single Cylinder Oscilator

**Bunkerbarge** · 21-01-2007

OK I'll start off with a story of my own little engine.

It all started somewhere in the early eighties when I was back at home with my Mum and Dad, between marriages, and my Dad was into car boot sales at the time.

He came home one day with a model boat that contained a little vap boiler and a single cylinder oscillator attached to the prop. Very simple and cheap and I fell in love with it. When I asked my Dad what he paid for it he said something like a couple of pounds. So I asked him if I could have it. "Sure" he says, "I'll let you have it for twenty" He was a Yorkshireman.

So me also being a Yorkshireman told him to stick it! What I did do though was take it apart and see how it worked. Next time back on the ship I made my own in the engine room workshop out of scrap bits I found all over the place.

The main body is made from plumbers brass compression fittings, soldered together and the piston and cylinder is made from a brass weight attached to a steel tape measure and used for sounding fuel tanks. The spring came from a compressor unloader and the flywheel was turned from a former out of an old copper pipe bending kit. All the other bits were turned from bits of scrap.

I had no drawings to work from and the only sketch I made was to determine the throw from the bore and stroke and to work out where to drill the ports.

At the end of the day it works!! I have had it running on compressed air a few times and I have never had any ambitions to put it into anything the whole purpose was simply to show my Dad and say "You won't sell me yours for a fair price so I'll make my own!"

porschenut · 21-01-2007

Good Story Bunk! Great Engine!
Euan

**Bunkerbarge** · 21-01-2007

I don't think it would do very well in a boat as it is quite a large bore for an oscilator, which use a lot of steam anyway. I'm sure the boiler needed to keep this little chappie running would sink the boat!!

**Bluewavestudios** · 22-01-2007

Very Nice work there Richard, I certainly have to admire your ingenuity in this one. Or should that be Enginuity..!!!

Regards........Mark

**Bunkerbarge** · 22-01-2007

Thanks Mark! Did you know that the title Engineer does not derive from the word Engine as most would believe but it actually is derived from the word Genius.

Not a lot of people (exept engineers!) know that

dipstick · 23-01-2007

i made a simply little oscilator engine at college, it took 3 days two machine up, and i think i still have the drawings somewhere in my room or workshop.

**Bunkerbarge** · 07-02-2007

Well the natural progression in developement of the Single Cylinder Oscillator is, of course a twin.

The first arrangement I have here is a horizontal parallel twin which was an Ebay buy a couple of years ago. What caught my eye was the elegant long rods of the pistons and the fact that I had never seen such an arrangement before.

As you can see there are two identical cylinders, each with it's own ports supplying steam at the correct time of the stroke. The big advantage now is that the cylinders can be arranged at 180 degrees apart so the engine should now be self starting.

Unfortunately this engine is not quite as well made as it looks and the crank webs are fixed to the crank with grub screws. These pretty quickly come loose and I now have to set up the timing again and try to come up with a more secure arrangement for the webs.

Nevertheless I still think it is a very attractive arrangement although for practical purposes it would need a lot of steam to drive it.

Another by far the more popular arrangement is the 'V' Twin as you can see in the picture of my model boat engine. This is, once again, another arrangement of two cylinders but this time we have taken it a significant step further and made it double acting. The means that steam is applied to both sides of the piston so the piston is actually driven in both directions. This has two major advantages namely the ability to reverse as well as self start and a good power to weight ratio.

These are the main reasons why they are so popular for model boat applications as steam propulsion units as they can now give complete control via a servo linkage and give a good amount of power for a small unit. The main disadvantage is maintaining a seal between the cylinder face and the main frame which can leak steam if not looked after. This tends to make them more suitable for an open boat where steam leaks are not so much an issue as they are in an enclosed boat.

So why did I put one in an enclosed boat? What a good question!!!!

dipstick · 07-02-2007

richard that really is a nice model you have got and i can see why it caught your eye.
to fix the problem of the webs coming loose loads of options like spotting though with a drill just to something from the grub screw to dig into. another option is file a flat on the shaft so that the grub screw is lower the diameter. or if you set up the timing right, scribe a line so you can put it back in the same position, and put a dab of loc tite on it and i would say to use 603 or 638.
hope it helps
chris

**Bunkerbarge** · 07-02-2007

They were the sort of things I was thinking of Chris.

**Bunkerbarge** · 08-02-2007

Taking the idea of the oscillating engine along it’s natural progression the next in line has to be a triple cylinder. There are certainly not many of these around in fact I have never seen any other apart from the one shown here. This was also an Ebay find and the big attraction here was the fact that not only is the engine a triple cylinder oscillator but it is also a radial engine.

Unfortunately at this time I only have the one very poor picture of it which does not very clearly show the cylinder arrangement so I will try to get a couple of better shots when I get home next time.

As with all radials the entire assembly of cylinders rotates and in doing so the cylinders oscillate and open and close the steam ports. This drives the pistons and in doing so rotates the assembly. It is a very interesting and clever piece of engineering but I have not had it steamed yet. It turns over quite successfully on compressed air but the boiler does not have a burner with it so I have not been able to raise steam with it yet. I believe the unit to be quite old and it has obviously been restored recently although not in the most sympathetic manner. There is a bit too much heavy gloss paint for my personal taste but the model does stand out and an exceptionally interesting piece and to see the whole thing rotate on air is amazing.

So that is as far as my collection of oscillators goes. Next we can go a bit further up the evolutionary scale and look at slide valves.