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EMC 125 1960
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
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