By Graham Meek

Prior to starting my apprenticeship the only steam engines I had built were a simple oscillating engine ½” bore by ¾” stroke built as part of the metalwork course at Grammar School, and a Stuart Double Ten, again during my metalwork course. As the school supplied the castings this model was retained by the school and placed in a glass case along with other engines built by previous scholars. Engines that were already present were a large beam engine, steam hammer and Sirius engine all from the Stuart catalogue which I found at the time (more on that later).

At about the time I started my apprenticeship Edgar T Westbury (ETW) had just started writing about the Gemini High Speed flash steam engine. Compared with my previous forays into steam this was a real departure from what I was used to and what I had grown up with. I wanted to build one, but my facilities at the time were only a Unimat SL, the Gemini was too big for this machine so copies of the articles were carefully stored away. As with a lot of hopes and aspirations other things get in the way, marriage, family, moving house and changing careers to mention a few. The original desire becomes a distant memory with a personal promise that "one-day".

Changing careers from aviation into the commercial world of photocopiers brought a whole new range of materials and parts into my modelling sphere. One such was the timing belt, which were all the rage on the cars of the day, which came in all sorts of sizes. One size in particular was just about right for my Gemini, so samples were procured and stored away with the plans.

Obtaining a larger lathe, a Myford Super 7 brought other distractions as these pages and those of Engineering in Miniature will testify, with it the Gemini becomes an even more distant memory. But, one-day! The years roll by quickly with work on workshop equipment, petrol engines, tractors and eventually writing taking centre stage until it is time to retire.

Now one thing that has been high on my wife's agenda once I retired was to clear the attic of my "junk". This comprised of mainly books and magazines, as I thought. I managed to fight shy of the task for two years but at the beginning of November in 2014 I finally capitulated and agreed to remove my pile of junk. A bookcase was purchased to store those books I wanted to keep and files were bought to take the magazine articles I wished to retain.

Those books I did not retain were distributed around my various friends. I bet their wives love me.

During the life's laundry what should appear but the Stuart Turner catalogue and the Gemini articles now faded beyond use. In the same box were the timing belts stored away all those years earlier prior to the house move. Also in the box was a reprint from Tee Publishing on the Gemini. I freely admit I had forgotten all about this book, but I was glad that I had it given that the copies were trash. Well, after I had cleared my pile of junk there was still a sizeable pile in the attic, it transpires that most of this belongs to my daughter from her Uni days.

At the beginning of December work had ground to a halt on my Fiat tractor in part due to the desire for a change but mainly due to the shortage of materials to carry on with the next phase. One night while sitting in the armchair perusing my collection of books and thinking this sure beats going into a cold attic. My eyes were drawn to Experimental Flash Steam by J.H.Benson & A. A. Rayman and reading through this I came across an ETW V4 engine design based on the Gemini lines.

He had proposed this design for a steam car that never made it beyond the design stage. This made me think of the Gemini engine. Now where was that book?

Sitting and mulling over the dimensions I had soon worked out in my mind that with a slight reduction in size I could make a 12 mm bore by 14 mm stroke version, so plans were drawn up for this. The Gemini engine at this scale works out at about ⅞ of the size of the original.

While the drawings for this engine were still on the drawing board so to speak I had played around with a stretched version to make a 3-cylinder in-line as well as a preliminary V-4. However the more I looked at ETW's V-4 design the more I was sure the valve for this engine was not drawn correctly or that I was overlooking something.

Brace of engines.

Putting this to one side work started on making the two and 3-cylinder versions. For about the same length of time as I had been wanting to make this engine I had also wanted to try a brass fabricated engine block. One other thing I wanted to try was turned connecting rods with the big-end cap fitting over a spigot on the rod via a turned counterbore. The resulting mating face becomes the big-end split line.

Work duly started about the second week of December with a self imposed deadline to finish the engines for the first week in February. From the outset to make the challenge even more interesting all the parts were to be made to ‘limits and fits’ and no part would be assembled until all the parts were made.

2-cylinder components.

The work went better than I expected and the deadline was met with few days to spare. The only other thing I did do differently was to fit silver soldered brass pistons with one pegged cast iron ring, in lieu of the cast iron pistons in ETW's design. I know brass is not suitable for flash steam but my intention for these engines, (one-day), is that they will only be used on slightly superheated steam.

The engines initially would run on about 40 PSI of air and had a sound comparable to any aero-diesel two stroke. The beat of the 3-cylinder version is curious. I have as will be seen from the photographs used balance weights on this crankshaft. I toyed for a long time about doing this. Some schools of thought say that they are not needed, but looking at a proposed 3-cylinder tandem design by Ricardo for General Motors, in Experimental Flash Steam, page 23, this shows balance weights fitted.

3-cylinder components.

This design did not go any further than a design exercise and was about the time in the early 70's when we were told our oil reserves were running out. I therefore decided if balance weights are good enough for Ricardo then they are good enough for me, but they are peculiar in appearance. I know they work and that they are needed as without them the engine does its best to walk off the bench while doing an impression of a cowboy on a rodeo horse. In passing it is interesting to note, looking back at the Ricardo engine, the drive to one of the two camshafts was by what appears to be a timing belt.

Both engines at this stage now tick over merrily at 20 PSI for the 2-cylinder while the 3-cylinder will go down to 15 PSI. As pressure is increased via the pressure regulator both engines accelerate
smoothly to a point just above 45 PSI when the compressor can no longer supply enough air to increase the revs further.
For longer periods of running it was decided that it would require some form of metered lubrication to the rotary valve. To meet this requirement a 1 mm bore by 1 mm stroke oscillating pump is driven off the back end of the rotary valve. During extended runs
on compressed air the pumps deliver just enough oil to keep this valve adequately lubricated, the excess goes via the pistons and out the uniflow exhaust ports.
Bolstered by the success of these two engines my thoughts returned to the V4 which I decided to tackle from a different angle. Wanting to retain the timing belt drive I set about using a longer 2-cylinder rotary
valve housing situated
between the cylinder banks, rather than ETW's lined housing in the block. The centre line of the valve was worked out so that by using larger timing gear pulleys, (which were all cut ‘in-house’), I was able to use the same timing belt.

At this time with out a great deal of drawing I was not sure if it was possible to use the same timing belt tensioner. I, therefore, decided to wait until the parts were assembled and try one off the other engines.

During manufacture of the other engines several spares had been made. Among these spares was a finished cylinder liner and piston. I, therefore, decided if I made three new cylinder liners with slightly smaller and lower uniflow ports, as well as three new pistons. These then could be used to replace those in the 3- cylinder engine and

Photos above:

3-cylinder crankshaft

Con rods (gap beween big end cap and con rod is intentional

Piston rings

Cylinder liner and piston - silver soldered bosses

Photos below:

Main bearing housings - scallop is to catch oil from main bearing

Three and two cylinder rotary valves

Oil pump details

those from this engine
used could be used in the V-4. With the crankshaft being only slightly longer than the 2-cylinder version it was necessary to reduce the original con-rod big end widths to just under 6 mm wide. With everything made and assembled I tried the timing belt tensioner off the 3-cylinder on the V-4. To my surprise it fitted perfectly and I must say I could not have done better if I had planned it. I therefore set about making a
new timing belt tensioner assembly to finish the engine off.
This engine was able to run straight away at about 20 PSI due mostly to the three cylinders being run in on the 3-cylinder engine and over the intervening weeks the pressure has slowly dropped to 15 PSI at tick over. Like the other two engines this engine accelerates away smoothly as soon as the regulator
pressure is increased and like the others it is limited by the compressor. The 3-cylinder was also treated to a new rotary valve with the original ETW timing. I have made these valves out of EN 16T, not the easiest material to use 1.5 mm slot drills on, and finished the outside diameter after milling with my tool post grinder.

Both engines with oil pumps and pipework fitted

My first attempt for the 3-cylinder valve used a longer admission period in an attempt to make the engine self starting. While the valve was a success in achieving this self starting requirement. It was felt during the subsequent running of this engine that this was not really a good move as the amount of air used, (and what eventually would be steam), was quite high when compared to the two cylinder version. The new rotary valve and the shorter uniflow exhaust port period has transformed the air consumption of this engine as well as the exhaust note, which is now not so harsh. Despite losing the self starting ability if the engine is rotated to just after Top Dead Centre (TDC) on No 1 cylinder. As soon as the tap on the compressor is opened the engine springs into life with as little as 15 PSI on the gauge. While I like all the engines I must admit the quirky 3-cylinder has become my favourite.

As regards the future the V-4 still requires an oil pump for the rotary valve and I am tempted to try a twin rotary valve head for the 3-cylinder, but that will have to wait. Back in my apprenticeship days the Gemini engine had been destined for a vehicle and there is a drawing on the computer for such an installation. ‘Mamog’, is part Unimog 411 in outline and utilises Mamod steam wagon wheels,
along with a gas fired transverse boiler.

I am currently trying to finish another project started about 10 years ago now, before my foray into writing took hold. I have started a 10 cc single cylinder 4-stroke diesel engine. The design is based on a design by Rex Swensen and like Rex's design I have initially made the engine compression ignition. The reasoning behind this was to get a working 4-stroke

Above: V-4 block and components.

design. Then with a new head, pre-combustion chamber, injector and injector pump it was hoped to get a true Diesel working, but can I master the injection pump. Various attempts so far have not been up to expectations, but I am making progress as each new design solves one of the previous problems.

Luckily there are more people trying to perfect these little engines around the world now than when I started and their help has been most welcome. Materials for the Fiat tractor have been obtained now and I will hopefully pick up where I left off on the Fiat, who know all of these might appear in print, (one-day!!).

Assembled V-4 engine.