The Atom Minor Mk3 - E T Westbury
E T Westbury's development of the Atom series of single cylinder 2-stroke engines began in the early 1930's and continued throughout the war. Originally designed at 30cc, 15cc and then 6.3cc capacities, the Atom Minor Mk3, the final evolution of the breed, was released in 1947 to conform with 6.0cc competition limits.
With its rotary induction valve, the Atom Minor Mk3 will swing a Ø12" x 6" pitch propeller at 6,500 rpm in standard trim. A tuned example, with a 10:1 compression ratio, was bench tested in 1945 on wartime "clear pool" petrol and returned 0.29 bhp @ 11,000 rpm, rev'ing freely through to 14,000 rpm. This would have provided 25mph performance in a 24" Hydroplane or 55mph from a 17", 6lb Tether Car! The design however was conceived primarily for model aircraft applications, where it can be mounted upright or inverted.
The ignition system proposed by Westbury offers simple cam-operated contact breaker points. You may decide to go this way or to use an up-to-date Hall effect system. Although designed originally to accept a 3/8" x 24tpi (now M10 x 1.0mm) threaded spark plug, most builders agree that the Rimfire VR2 (1/4" x 32tpi) is a more pleasing match, aesthetically. You'll find more information in our Engine Accessories section.
Many builders choose this as their first model engine. The build is very well documented within Westbury's book, "The Atom Minor Mark III" and, as a 2-stroke, avoids the challenge of valve timing.
The Atom Minor Mk3 in Action