MOTOSACOCHE

750cc Type 712 / Watsonian Oxford Sidecar -1 931

High-class F-head

For its big V-twins, Motosacoche was an advocate of the F-head layout, with overhead intake and side exhaust valves. It had a compact combustion chamber that dispersed the burnt gases, without overheating or distorting the cylinder head. Problems which were inherent with engines using overhead exhaust valves. In 1931, these engines were succeeded by MAG V-twins with both automatic intake valves and two side-valves.

Cost-Saving Exercise

The first MAG F-head engines were 500 and 750cc units, followed by 1000 and 1100cc models. In 1922 came a 600 – built in France to save money – designed to compete with war-surplus Harley and Indian machines, which were sold at low prices after WWI.

Luxurious Chair

The Paris Salon was the beginning of the end for the F-head MAG engine, when a new 850cc Grand Luxe side-valve V-twin, designed by Bert Le Vack, was announced. But the 500cc F-head V-twin came back from the dead in 1934, while the classic 750 continued on its way, with a magdyno mounted longitudinally on the right side of the crankcase. Even though Motosacoche catalogued an own-make touring sidecar, the 750cc Type 712 is coupled to one of the most famous British-made "chairs," the Watsonian, shown here in its coachbuilt "Oxford" version. It had a wooden frame clad in leatherette-covered plywood. It cost $120 – one-third the price of the bike – which included a proper door, button-down fabric roof, trunk with external access and in front of the Float-on-Air

inflatable seating, an optional child seat.

SPECIFICATIONS

Engine: 748cc (72x91mm) air-cooled 45-degree V-twin four-stroke

Valves: side exhaust, overhead intake

Fuel System: Amal carburetor

Transmission: Sturmey-Archer 3-speed, chain final drive

Suspension: girder forks (front); rigid (rear)

Brakes: drum (front & rear)

Wheels: interchangeable 3.50x19 inch (front & rear)

Weight: 436 lb (solo); sidecar 159 lb

Heavyweight sidecar outfits such as this one were fighting a rearguard action against the popular small automobiles that were flooding onto the roads of Europe in the 1920s and 1930s.