The Atlas 3 cc spark ignition engines were produced during 1946 by the Atlas Motors company of Studham, near Dunstable in Bedfordshire, England. Interestingly enough, this was one of a number of small precision engineering firms owned by none other than D. A. Russell of “Aeromodeller” magazine fame.

The Atlas 3 cc model was produced in two distinct variants. These were very similar, the main difference being that the Series I version had a cylinder head which formed an integral component of the main cooling jacket, while the Series II had a separate bolt-on head. The displacement of these engines has often been cited as 3.5 cc, but direct measurement plus advertising statements confirm that the true displacement was only 3 cc.

The Atlas engines are often confused with the very similar but slightly larger 3.5 cc and 4 cc H-P models which were subsequently produced from early 1947 onwards by a different successor company, Henleyston Products of Barnet, Hertfordshire. In fact, distinguishing between the two is quite easy. Apart from the displacement differences, the Atlas models bear serial numbers having an A-xxx configuration, while those produced by Henleyston Products bear a serial number having an M-xxx format. Moreover, the H-P products are clearly stamped as such on their backplates. The distinction is well worth making, because the Atlas models are far rarer than their H-P successors.

Full details plus a test of the Atlas engines are included in my article on the H-P range which may be found elsewhere on this website.