Benelli 250 1939
In 1939 Benelli machines appeared in the Isle of
Man for the first time; two were entered for the Lightweight T.T. One
retired—and the other, ridden by Ted Mellors, won by almost four minutes.
The machine that scored this success is interesting because its conception and
general pattern established a style that was to become commonplace after the war
in Italian 250 and 125 racers. Light alloy was used very extensively, for barrel
and head and for a bolted-on cam-box. A gear train drove twin overhead camshafts
completely encased but operating valves with exposed hairpin-type springs.
The magneto drive was by an extension of the gear
train forward of the crankcase. Astern a four-speed gearbox was bolted up to
form a unit. Another feature, pioneered by Guzzi, of Italian lightweight-styling
was the use of an outside flywheel. The machine had a deeply finned crankcase, a
large oil tank and an oil cooler, in an endeavour to promote cool running; all
this proved a bit unnecessary in the 1939 race, for it was exceedingly wet—so
wet in fact that for the race a hastily improvised cover was fitted over the
The rain slowed the race speed to a mere 7425
m.p.h. Graham Walker rode the little model just after the race and reported it
to be "unburstable". No rev-counter was fined and Ted Mellors told him to rev it
"until the exhaust note doesn't alter". This was about 8,200 r.p.m. on the level
in top or 9,000 in the gears—a top speed of about 110 m.p.h. which was still
good for a "250" twenty years later.
Engine: single-cylinder 250 c.c. d.o.h.c; light-alloy
cylinder and head; gear drive to camshafts. Ignition: magneto.
Transmission: chain drive via four-speed gearbox. Frame: single down-tube
cradle, with swinging-fork
rear suspension controlled by "plunger-type"
spring boxes. Forks: single-spring girder with friction dampers.