The Atom Minor Mk 3 - Edgar 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 propellor 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 primarly 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 our up-to-date hall effect system, the TIM-6. 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 Accesories 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.

This 50 page, small format book was released in 1947 at a cost of 3 shillings (£0.15/$0.25) including postage!

The book's first review in the Model Engineer magazine in November 1947 announced:

"The miniature petrol engine described in this book is of 6cc capacity and has been developed primarily for use in model aircraft. Its design and construction have been carefullly planned with a view to ensuring that the merest novice with limited workshop facilities can build one without trouble. The book describes and illustrates in detail how the various castings and parts should be machined and, provided that the instructions are followed, the constructor can rest assured that the results of his efforts will be a little engine which will give him absolute satisfaction. Mr. Westbury's instructions are clear and concise, while the illustrations - mostly line drawings - leave nothing to be desired"

Although re-printed many times in the past 60 years, no one has thought to correct 3 errors in the drawings. This doesn't affect the value of the construction advice but builders should order a copy of the drawing also - which is correct.

The kit includes all of the raw materials needed to complete the Atom Minor Mk3 as originally designed. Please remember however that our full material kits do not include electrical components (points, coil, spark plug...) which can be found in the IC Engine Accessory section.

The bill of materials includes 5 aluminium castings together with sawn lengths of bar material (free cutting and high tensile steel, aluminium, bronze, cast iron, brass, Tuffnol, silver steel and spring steel) and fasteners.

If you want to minimise shipping costs or if you are particularly well stocked with supporting materials, you may prefer to order just the essentials. This item buys the 5 castings available for the Atom Minor Mk3:

Body, Cylinder Head, Bearing Housing, Rear End Plate, Contact Breaker Bracket