The DOT factory planned to contest the 1953 Isle of Man TT races in 1953 with three twin cylinder 250cc rotary valve motorcycles,
fitted with engines supplied by Frank Aspin. Three prototype engines were delivered and tested, apparently delivering 28 bhp,
which was considered satisfactory for a prototype. I am sure it should have been, they should have been very happy with 28 bhp from a 1953
250cc engine, far in excess to the general British engines. Given my comments elsewhere, I wonder if that was a figure provided for them by
Frank Aspin and they took it at face value. Six frame sets were commissioned, which had trailing link forks, and based on this slim information,
Bob Tait made his drawing on the main page. The engines were 52mm bore by 58mm stroke driving a four speed Burman gearbox. A 350cc version was discussed at
61.5x58mm to contest the Junior races. The drawings that have come to me are in poor condition, very heavily foxed in many areas.
To make some progress I have traced the main outlines of the engines, no fine detal or dimensions for the moment.
Click to enlarge