May I hasten to write, very belatedly (the December MOTOR SPORT has only just arrived), a word or two in explanation of the apparently under-powered L.P.T.B. A.E.C.s mentioned in Mr. J. Lowrey’s “Thoughts on P.S.V.s.”
Being controlled by a governor, the maximum power output of a diesel can readily be cut down to any desired degree. L.P.T.B. have adopted a policy of so reducing output to a figure considered adequate for normal service in order to economise in fuel by preventing unnecessarily violent acceleration. As far as I remember, L.P.T.B. engines are set to give about 87 h.p., the same engine normally being set at about 95 h.p. for passenger work and about 105 h.p. for commercial work. Power output could be increased to either of these figures by a five-minute adjustment to the fuel pump.
The fierce changes on the Wilson box are, I agree, vastly disturbing to standing passengers, but are easily avoided by ,a little care on the part of the driver. The A.E.C. version of the Wilson box is one of the most pleasant pre-selector boxes that I have used, because the ratios are pre-selected by a normal-sized gear
lever moving in a gate, not the large or small lever moving in a quadrant that one finds on a private car. This end is achieved very simply by arranging the gear-selecting cams on the camshaft inside the box in a different order from the usual. In the normal box, cams are arranged to select gears in the order in which they are selected, i.e., reverse, neutral 1, 2, 3, 4. On the A.E.C., the order is reverse, 1, 3, neutral, 4, 2. This camshaft is then linked by a rod to the ball-jointed gear-lever which works in an H-shaped gate which allows the lever to move twice as far forward for 1 as for 3, and twice as far back for 2 as for 4. Thus, by putting the lever in the appropriate slot and moving it as far as it will go, the correct gear is selected. Reverse is obtained by lifting the lever and pushing it on through first.
A few of the refinements fitted to the RT-type L.P.T.I3. chassis, the latest type of A.E.C. appearing in London streets, may be of interest to the sportsear enthusiast. These include a rubbermounted 9.6-litre engine (larger than any predecessors) with the usual fluid flywheel. The gear-change of the preselective box is operated through compressed air by a pedal of the same size as the accelerator. The brakes are also compressed-air operated and are disconcertingly light in operation, and are automatically adjusted for wear by a mechanism incorporated in the shoes. It is also interesting to find the dynamo and air pump banished from under the rather full bonnet to a position by the gearbox and driven by a small HardySpicer jointed shaft running from the engine timing gears under the driver’s seat.
Also of great interest are the 10 Leylands fitted with the Leyland-LysholmSmith hydraulic drive, which are operated experimentally by the L.P.T.B., though this transmission is in regular production by Leylands. It is an infinitely variable ratio transmission, operating more or less on the fluid flywheel idea, but so arranged as to give the required torque increase, which, of course, the normal fluid flywheel does not. The most interesting feature of the Leyland transmission is the provision of a manuallyengaged direct drive, the use of which overcomes the big snag of power-loss and heat generated by the somewhat low efficiency of the hydraulic drive.
To ride in a vehicle so equipped gives a very peculiar sensation. The vehicle takes off smoothly when the driver accelerates the engine, and thereafter the vehicle accelerates steadily while the engine speed remains constant. It is, in fact, quite difficult to realise, when seated, that the vehicle is accelerating. Then, at a speed which I estimate at about 20 m.p.h., the driver declutches and engages direct drive, after which all is normal until the occasion arises when a change down would normally be indicated, when the hydraulic drive is reengaged. As regards the Q-type A.E.C., my driving experience is nil and my riding experience very little, but I can remember
a few mechanical details. The 7.7-litre oil engine is based on the usual A.E.C. engine, but is left-handed, having all its auxiliaries—dynamo, fuel pump, water pump and exhaust manifolds—on the right and even rotates anti-clockwise, I think. Also, the sump and cylinder-block faces of the crankcase are not parallel, so that the block leans outward. The radiator, engine and separately mounted Wilson gearbox are slung outside the off-side frame members, the drive passing at a very acute angle under the frame member to a rear axle with the final drive offset close against the off-side spring. Advantages of the design were increased passenger space, easily removed engine and gearbox, and more equal axle loading.
Other ‘unorthodox L.P.T.B. vehicles are the flat-engined Leyland “Green Line’s coaches, with an in-line 6-cylinder engine lying on its side and a number of rearengined 20-seater Leylands.
Joe Lowrey’s notes on the Derby were also very welcome, and recall my quite lengthy visits to the Derby stand at the Motor Shows, where the stripped chassis were well worth careful study. I am, Yours, etc.,
J. S. MOON (Capt., R.E.M.E.).