947 A.J.S. "PORCUPINE". Probably the unluckiest
design ever to emanate from the Woolwich A.M.C. factory as far as the T.T. races
were concerned was the racing twin announced in May 1947 and, because of its
peculiar cylinder-head finning, quickly dubbed the "Porcupine". In its eight
years of development it scored successes everywhere—except in the T.T. Few
racegoers cannot have heard of the cruel luck that befell the late Les Graham
who, when leading the 1949 "Senior" very comfortably, had a magneto armature
spindle shear when almost in sight of the finish.
The engine, designed with a four-speed gearbox in
unit, had its cylinders lying almost horizontal. Primary drive was by gears (the
engine ran "backWards") and the entire unit had originally been intended to
include a supercharger mounted atop the gearbox. Twin overhead camshafts were
driven by a gear train carried in a Y-shaped case on the offside of the unit. A
full duplex cradle frame, with swinging-fork rear suspension, had the
by-then-famous "Teledraulic" front fork similar to that pioneered during the war
on W.D. 350 c.c. Matchless machines. Both front and rear suspension had 3 in. of
movement and the rear units were of the oil and air type.
In their first T.T. the A.J.S. twins were too new
to do more than be in a "useful"' position if anything went wrong with the
Norton stars. Nonetheless, Les Graham was only 3 m.p.h. down in sixth place at
the end of six laps—his chain came off at Governors Bridge on the last lap and
dropped him to ninth finishing position after pushing in. "Jock" West had
battled with a slipping clutch on the opening lap and this took him 84 minutes,
but by cracking round and making second-fastest lap of the race he finally
worked up to finish fourteenth. If that clutch had been O.K. at the start. . .
Engine: parallel-twin 500 c.c. d.o.h.c; light-alloy cylinders and
cylinder-heads; gear drive to camshafts.
Transmission: spur gears to four-speed gearbox in unit
with engine; final drive by chain. Frame: duplex cradle with pivoting-fork rear
suspension. Forks: A.M.C. "Teledraulic" telescopic.