Above: right side view
Below: left side view



Cylinders: 1
Type: Vertical single with atmospheric intake
Bore: 1.625”
Stroke: 1.875”
Displacement: 3.94 cu in
Compression Ratio: 6:1
Ignition: Spark plug
Cooling: Air
Fuel: Gas or 15% nitromethane/methanol mix
Max. RPM: 6,000
Est: Horsepower: 3


Background -- Not long before this engine came into being I had built a very light, Whitehall design, rowing boat. Rowing is very good exercise but the range can be limited. I had the thought that an engine could be designed which could be governed and light enough to mount on this boat. This would extend the range (yes, I've heard of outboard motors, but that would have taken all the fun out of it).

This air-cooled unit uses an atmospheric (automatic) intake valve. Many older engines used this system; there’s no cam on the spring-loaded intake valve that opens from cylinder vacuum when piston is on down stroke. Thus, there’s no control over valve timing.

Construction -- This engine used castings I produced in my own little foundry (click here for more on castings). The rocker cam, a timing belt driven cam, was used for the exhaust valve. A flyball governer was used to block the intake cam and thus control the engine speed. The displacement was 3.9 cu.in. which is larger than I usually build.

Operation -- The final results were mixed. It ran okay and governed at about 3000 r.p.m. The main problem was that the governing was quite abrupt because of the fairly light flywheel. I found that I'd need a much larger flywheel to tame this engine, which would defeat the purpose of a light, low-speed boat motor. Well, you don’t win them all. It was not prudent to carry the development any further. The automatic speed control did actually work okay, as the max speed without the governer was about 4500 r.p.m.

On Spark Plugs and Glow Plugs...

It was difficult to find small commercial spark plugs so I built quite a number of my own using Corian as the material for the insulator. For most of my later engines I changed to glow plugs. Although spark plugs give a bit better flexibility, the final performance of glow plugs is almost as good and a lot simpler. Almost all model engines now use glow plug ingnition.

In multiple cylinder engines however, it takes a lot of amperage to light the glow plugs since they are in series. Also, if one plug goes out it usually takes out the rest out due to the increased current draw.


Detail of valve actuation mechanism.

(click on buttons)



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