ADM

500 Grand Prix -1983

Built like a Swiss watch

It was the sensation of the 1983 French GP. Ridden by Andreas Hofmann, the ADM never passed the experimental stage, and it was never seen on the racetracks again, but it was so advanced technically that it deserves to be remembered.

Five Years' Development

The ADM was designed by a young Swiss engineer, Charles Auf der Maur, who devoted five years of his life to its development. The keystone of his machine was its engine, an original "flat-four" with a longitudinal crankshaft, rather like a Gold-Wing power unit turned through 90 degrees. The primary transmission was by bevel gears driving an intermediary shaft which actuated the ignition, driving the rotary distributors by cogged belts. The gearbox, originally from a Yamaha TZ750, was more conventional, but this narrow engine configuration had been chosen so that the ADM could be built exceptionally low; it rode on 16in wheels, still an uncommon size.

The End of the Road

Haunted by the usual financial problems of a one-man workshop, as well as by the unavailability of suitable tires in his chosen dimensions, Auf der Maur finally threw in the towel. Nowadays ADM designs and builds engines for sidecar outfits raced in speed events as well as in motocross.

SPECIFICATIONS

Engine: water-cooled 495cc (54x54) flat-four two-stroke

Power Rating: c.125hp@ 14,000rpm

Valves: 4 rotary valves

Fuel System: 4 Dell'Orto carburettors

Transmission: 6 speeds

Suspension: telescopic fork (front), cantilever (rear)

Brakes: twin disks (front); disk (rear)

Wheels: 11/56 -16 (front); 13/61-16in (rear)

Weight: 260 lb

Despite appearances, the ADM was a short, compact machine. It was particularly low-built, but nevertheless its performance proved disappointing.