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BEFORE the days of the war the Trump-Jap machines, which were associated with the name of F. A. McNab, were well known in competition circles, and especially so on Brooklands.
During the present year the name has been revived, and Trump Motors, Ltd. of Byfleet, are again in the field, with Mr. McNab actively engaged in the design and track riding of the machines, and Col. R. N. Stewart in control.
The idea, obtaining in the production of these machines is that a series of sporting models shall be made to suit the requirements of the class of rider favouring this type of mount.
A New 4 h.p. J.A.P. Engine.
An 8 h.p. sporting model, having the J.A.P. twin engine, was illustrated in our issue of the 4th inst. on page 141, and another model which is being brought forward is the 4 h.p. single, engined with the new 550 c.c. J.A.P. unit.
The machine follows a conventional lay-out, having Druid forks and a frame with curved top tube. The peak of the saddle is hinged to the latter, the springs being mounted on supports which are carried from the top back stay bridge. 650x65 mm. tyres are fitted, and transmission is by chain and belt through a Sturmey-Archer gear box. The latter may, at option, be one of the special type for speed work, with clutch but minus kick-starter, and with very close gear ratios, or the standard box with kick-starter and the ordinary low bottom and middle ratios.
As yet, the new 550 c.c. single-cylinder J.A.P. engine has not become familiar to the majority of motor cyclists, but it will be seen that it follows the lines of the 250 c.c. and 350 c.c. models, which were used with so much success in the T.T. The sparking plug is inclined the rear of the inlet port, and large aluminium valve caps with radiator flanges are used.
A detail refinement is the crank case release on the timing gear, which is arranged between the valves, so as to blow enough oil spray on to the stems to prevent the valves wearing badly in their guides.
The Motor Cycle, August 25th, 1921
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