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THE LATEST DAIM ER DOUBLE-DECKER
THERE is always "something different" about a Daimler vehicle, no matter whether it be a private car or a big commercial machine. A short time ago the almost uncanny silence of the sleeve-valve engine was the outstanding feature of the Daimler Co.'s products. Then came the transmission development of the Fluid Flywheel and the epicyclic gearbox. Now there is a poppet-valve engine which closely rivals the sleeve-valve type in the matters of silence, power output and general behaviour. These later developments were included in the vehicle—a double-decker capable of carrying 52 passengers—which we recently tested for a day in the Midlands.
The newest feature of the machine is, of course, the poppet-valve engine, and, as we were impressed by its design when we 'inspected the 1932 Daimler models, it is only natural that we should pay particular attention to the behaviour on the road of this unit. We can say that, right from the start of our run, the engine behaved in an exemplary manner and evinced all the desirable characteristics which have made the name of the Daimler Co., Ltd., Daimler Works, Coventry, famous for over a quarter of a century.
The particular vehicle chosen for our test was a CP6 model, which, with respective wheelbase and track dimensions of 15 ft. 6iins, and 6 ft. 31 ins. (front), 5 ft. 107-16 ins. (rear), has an overall length and width of 24 ft. 101 ins. and 7 ft. 51 ins. respectively. The loyal body with which the chassis was equipped had 26 seats in the lower saloon and 26 on the upper deck, all being roomy and comfortable.
As tested, the vehicle carried a load of metal blocks. il22 the aggregate weight amounting to 3 tons fi cwt. 2 qrs., or the equivalent of 52 passengers and the conductor. Added to this amount was 4 cwt. for equipment, etc., which is usually accounted for in the chassis weight, being such items as fuel, oil and water ; the total weight of the vehicle as tested was exactly IA) tons, and so came within the regulations regarding maximum axle weights.
At first we tried the vehicle from the point of view of an ordinary passenger, and were duly impressed by the general stability and easy-riding qualities of the bus, both at low speeds in congested areas and at high speeds on the open roads. Even at the back of the vehicle there is only a small and relatively easy motion, with little of the bumping and hard " thuds " which used to be inseparable from service-type double-deckers.
Another urominent characteristic, from the passengers' point of view, is that a high degree of mechanical silence of the power-unit and transmission has been achieved. For all practical purposes the engine runs inaudibly when ticking over, and the slight -crescendo of noise which inevitably takes place as the crankshaft • speed is increased is truly moderate.
When running at 25 m.p.h. one can converse with a fellow passenger without it being necessary to raise the voice, whilst the comparative silence of the indirect gears, during both acceleration and hillclimbing, is most commendable. Again, one might mention the action of the Fluid Flywheel. The power take-up is always smooth, and, even if the gears be handled roughly, there is a notable absence of transmission snatch, due to the action of the oil in the flywheel casing.
We can now turn to a consilleration of the vehicle from an operator's and driver's point of view. First, the engine is built on thoroughly robust lines, with a girder section for the crankcase in order to promote general stiffness, whilst the reciprocating parts, although amply strong for hard service, are relatively light in weight, so that inertia loads on the engine are reduced to a practical minimum.
The lubrication system has received particular attention. All the major bearings in the engine, of course, receive a supply of oil under high pressure, but an innovation is that the gudgeon pins are pressure fed as well, holes drilled in the webs of the connecting rods conveying the oil from the big-end bearings to the gudgeon pins.
Precautions have been taken to avoid any possibility of the pistons, cylinder walls, etc., becoming dry, or at any rate insufficiently lubricated, when the engine is first started up from cold; in these circumstances the oil is very thick. This protection takes the form of a " bleed " drilled in each of the big-ends of the connecting rods, in such a position that a stream of oil is slung out when the crankshaft is revolving, a proportion inevitably reaching the cylinder walls and piston skirts.
By reason of special attention having been paid to the porting arrangements, the engine fires regularly, even at very low speeds, and when properly warmed up we were unable to find a "flat spot" anywhere in the speed range. The power of the engine is reflected in the performance of the vehicle, and when it is B24
realized that the fully loaded bus could accelerate from 10 m.p.h. to 20 mph. in 20 secs. and to 30 m.p.h. in 40 secs., using only top gear, the torque characteristics of the unit at low and medium speeds ' must be considered good.
The action of the Fluid Flywheel, of course, puts a new complexion on a vehicle, for it is quite possible on level going, or even sou, a slight upgrade, to start off in . top gear without it being necessary to manipulate the " clutch " with extreme caution, as is the case in a transmission of normal layout. Actually, we carried out this experiment against the stop-watch and attained in top gear from rest a speed of 20 m.p.h. in 36 secs.
Subsequently, we repeated this test, but used all four gears, with the result that a speed of 30 m.p.h. was reached in 34 secs.—a fine performance. In "third," the engine evinces a marked liveliness, for we were able to reach 10 m.p.h. in 5 secs:, 20 m.p.h. in 16 secs., and 28 m.p.h. in 27 secs, from a datum of 5 m.p.h.
The Fluid Flywheel and epicyclic gearbox really come into their own when hilly districts have to be negotiated. Apart from the fact that the gears are absurdly easy to engage and it is well-nigh impossible to " muff " them, the 'lightning rapidity with which successive changes can be effected is most pleasing.
Although the action of the self-changing gearbox is, by now, fairly well known, it might be worth recording the sequence of operations for the benefit of those readers who have missed articles dealing with this transmission in previous issues of The Commercial Motor.
A gear quadrant, situated just beneath the steering • wheel, has a lever which, to all intents and purposes, is a pre-selector, for any gear can be selected by the lever and engaged merely by depressing and releasing the left-hand pedal. Thus, when starting off in "first,' the pm-selector lever is placed opposite the first notch in the quadrant, the gear-engaging pedal is depressed and released again, when, by speeding up the engine, the Fluid Flywheel begins to take up the drive.
Second gear should, in the meantime, be pm-selected, and, when the time comes, the pedal can be depressed and released again to enable the gear to be engaged. In the ordinary way, when running in top, the preselector lever should be moved to the third notch in the quadrant so that, the moment it becomes imperative to change down, a quick depression of the pedal suffices to complete the operation.
To give an idea of the accuracy with which the action of the Fluid Flywheel can be gauged, it might be mentioned that it is possible to bring the vehicle to rest on an up-grade in top gear and to hold it stationary without using the brakes, merely by suiting the torque transmitted through the flywheel to the gravitational tendency of the vehicle to run backwards clown hill.
The hill-climbing powers of this latest Daimler product are well up to the average, and, in our opinion, it would be impossible to find a hill on. a service route in any town or city in this country, at any rate. which would baulk the bus, even when fully loaded. By reason of the action of the Fluid Flywheel the driver is not fatigued by constant application of the service and auxiliary brakes, for the capacity of the Fluid Flywheel to hold the vehicle on a steep incline serves another purpose in that it permits a quick getaway to be achieved after a traffic block. All moderate gradients can be climbed in " third " or "top," leaving second gear for the really severe type of hill, whilst first gear is merely an emergency ratio. The braking system calls for favourable comment, for the three-servo layout is particularly efficient and, at the same time, a light pedal pressure is achieved. There is practically no delay in the retarding action of the brakes from the instant of application of the pedal and, what is even more important, the movements are well graded and the retardation appears to be directly proportional to the amount of energy exerted by the driver. Steering, which, by the way, is of the Marks type, is accurate and is entirely free from shock or wheel "kick." On the vehicle tested, however, we formed the opinion that the reduction mechanism was a little too tight., but as this is a matter only of adjustment and concerns individual tastes, it is a point of no moment