EMC 125

 

 

 

1960 E.M.C. 125. Although this machine was entered at meetings in i960 as an E.M.C, most spectators shared an open secret—that the power unit was an experimental model from the de Havilland engine factory where Dr. Joseph Ehrlich (the "E" of E.M.C.) was busily developing a series of two-stroke engines for that concern—and what better place to assess development than on the race track?

The bottom half of the unit followed fairly conventional high-speed two-stroke practice, in fact at first the model employed continental castings, machined in the D.H. factory, for the crankcase. A rotary inlet valve was used, breathing through an Amal G.P. carburetter. It was the top half of the engine that was the novelty, employing Ehrlich's patented "booster-ports". In this system, when the piston is at the top of its stroke a series of ports, usually two, are uncovered in the cylinder wall.

These ports are big enough to hold a few c.c. of mixture and have only the one opening each. When the piston descends it compresses the gas in the crankcase, and in the open ports.
Farther down its stroke, at the point of maximum crankcase pressure, and just before the transfer ports open, the piston skirt shuts the ports, trapping some compressed gas.

As the piston nears the bottom of its •stroke, the charge of mixture transferring into the barrel through the transfer ports has almost stopped; the extra ports are uncovered, releasing the compressed gas into the base of the barrel. This gas helps to eject the exhaust gases and also to fill the barrel with "good" mixture—to boost the charge, hence the name.

Considering that the unit was raced in a frame employing obsolete parts from an old E.M.C.-Puch racer of the early fifties, it performed exceedingly well, often being among the leaders and with several fastest laps to its credit. At the time of writing it is still being developed. . . .

SPECIFICATION
Engine: single-cylinder 125 c.c. two-stroke; watercooled. Ignition: coil.
Transmission: gear primary drive to six-speed gearbox in unit with engine; chain final drive.
Frame: duplex cradle with single top-tube and pivoting-fork rear suspension.
Forks: telescopic.

A British prototype with a two-stroke engine was built solely to show that people's reservations about two-stroke motorcycle engines were unfounded. The two-stroke prototype aroused a great deal of interest for its technical features and chalked up fine placings in world championship racing.

This motorcycle was the EMC 125, which was built by De Havilland from a design by Joseph Ehrlich. The EMC looked like a copy of the famous MZ 125-250 and, like the German motorcycle, had rotating-disk distribution. Nevertheless the EMC was strikingly different from the German two-wheeler because of a construction detail that Ehrlich had patented in 1956.
Inside the cylinder, aligned with the transfer ports, there were two "lungs," or cavities shaped like light bulbs. These "lungs" were booster ports where some precom-pressed gas accumulated during the compression stroke. With the addition of the gas that entered through the normal transfers, an almost optimum capacity was achieved in the combustion chamber.

The EMC 125 made its racing debut in 1960, ridden by Rex Avery, and the motorcycle turned in fine performances during that season's world championship. Although it was ridden in subsequent seasons, it was not entered on a regular basis, nor were good racers available to ride it.

Motorcycle: EMC 125 Manufacturer: Joseph Ehrlich, De Havilland plant Type: Racing Year: 1960
Engine: EMC single-cylinder, two-stroke, rotating-disk distribution, two transfers and booster ports. Displacement 123.6 cc. (54 mm. x 54 mm.)
Cooling: Water
Transmission: Six-speed block
Power: 21.2 h.p. at 10,400 r.p.m.
Maximum speed: Over 100 m.p.h.
Chassis: Double cradle, continuous, tubular. Front and rear, telescopic suspension
Brakes: Front and rear, central drum