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DENNIS LANCET HI BUS S AN IMPRESSIVE DEBUT

25th May 1945, Page 26
25th May 1945
Page 26
Page 27
Page 28
Page 26, 25th May 1945 — DENNIS LANCET HI BUS S AN IMPRESSIVE DEBUT
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Road Test No. 301

IT has been known for some time that Dennis Brothers, Ltd., of Guildford, had something new to offer the road-transport industry in the shape of an oil engine. Whilst we are not yet permitted to give a full technical description of this unit, we are, nevertheless, able to give our readers some of its leading dimensions together with our impressions of its performance in the new Dennis Lancet III passenger chassis.

The engine is a six-cylindered unit having a bore of 105 um. and a stroke of 146 mm., dimensions which give a piston-swept volume of 7.58 litres. It has four overhead valves per. cylinder, and a seven-bearing crankshaft. The crankcase and cylinder block are cast in one, the alloy cast-iron cylinder liners being of the

wet type. , The particular chassis under review , is intended to carry the largest single-deck body within the limitaticins imposed by existing regulations, and the following is a general description of its main features. , From the engine, the drive is taken through a twoplate dry clutch, having a friction area of 429 sq. ins., to a five-speed overdrive gearbox. A two-piece propeller shaft is used, that between the gearbox and centre bearing being of the Layrub type, and that running to the rear axle a Hardy Spicer. The rear axle is an underslung worm-driven component.

As tested, the ratio of the axle was 6.23 to I, but there is an alternative axle, the reduction in which is ,5.66 to 1, the choice of either being, of course, dependent upon the type of service on which the vehicle is to be used. • The overall gear ratios with the 6.25 to 1 axle are as follow : Overdrive, 4,3; fourth, 6.25; third, 9.68; second, 18.47; and first, 32.37 to 1; reverse, 41.62 to 1.

Between the springs the robust front axle is of H , section, and beyond the springs it is circular in order to provide maximum torsional rigidity under the action of the brakes. At the deepest part, the frame section is 3.362 ins., with websmeasuring 3.375 ins.; the thickness is .212 in. In order to facilitate the removal of the engine, the front cross-Member is made detachable. Steering is by Dennis. worm-and-nut mechanism in conjunction with a sprung wheel. The Dennis concern is responsible for the design and manufacture of the brake shoes, which are operated on the Lockheed hydraulic system in conjunction with a Clayton Dewandre servo, having a 175 mm. cylinder.

Semi-elliptic springs are employed front and rear, andthe standard equipment provides for the use of 9.00 by 20 tyres.

The machihe used for our road test was a 32-seater, single-deck bus, owned by the Aldershot and District Traction Co., Ltd., and taken direct out of regular service for the occasion. The speedometer showed that it had just under 10,000 miles to its credit, although, in every respect, the machine had the appearance of a showroom model. _ , As taken over at Surbiton, the machine was artificially ballasted to the equipment of 24 passengers, and, in addition, there was the weight of five actual passengers, excluding the driver. In order to pick up two further persons, it was decided to make a

straight rim from Snrbiton to the Dennis works at Guildford and, en -route, to conduct the first part of the fuel-consumption test.

-Perhaps the first feature that one is out to note when there is an oil engine under the bonnet is the smoothness, or otherwise, of its general running; a most important consider tign in the case of a passenger vehicle. At the outset, we were particularly impressed with the almost entire absence of vibration and, at anything but idling revs., the unit was every bit as smooth running -as a petrol engine. This quietness and absence of fuss was characteristic of the complete chassis, which

was noticeably free ofmechanical

noises throughout. The above diagram On the overdrive and travelling atof valve operation

the governed speed of 48-50 m.p.h., one had the experience of really pleasurable motoring. For the fuel-consumption test the maker had fixed up a special half-gallon tank alongside the radiator, the change-over being effected merely by manipulating a couple of taps. The Machine was pulled up at the start of the Fair Mile, at Cobham, and the fuel in the gauge adjusted to give the dead half-gallon. On this run the consumption was equivalent to 16.8 m.p.g. On the return route, later in the day, the figure was 17.6 m.p.g., and thus we got th6 excellent average of 17.2 m.p.g-. For the most part we ran in the overdrive ratio, and there were no stops for traffic or other considerations.

Arriving at the works, the machine was put on the weighbridge and, after picking -up our two extra passengers, we made for a hill off the Hindhead road. This 'climb is of fair length and reaches a maximum steepness of 1 in 41. To say that the vehicle played with the hill is a literal truth. Branching off this hill at its steepest point is another hill, the gradient at the point of juncture being 1 in 3. The machine was actually stopped on this gradient for photographic purposes, and the ultimate negotiation of the turn demanded extremely tricky driving. The machine acquitted itself in an exemplary fashion under conditions with which it Would probably never have to contend in normal service.

The next test was connected with the braking. Of Dennis design and manufacture, the brake-shoe gear, as previously mentioned, is operated by Lockheed hydraulic mechanism in conjunction with a, Clayton

• Dewandre servo system and Dennis exhauster pump. The stretch of roadway chosen has a cement surface and at the time of the test was dry.

From a speed of 30 m.p.h., the vehicle was brought to rest on a dead-straight course in a measured distance of 47 ft. 6 ins., which gives an efficiency figure of 65 per cent. _ It Was intended to carry out further tests, but, owing to the ballast weights not being so securely fixed as they might have been, it was decided to forgo them.

In the matter of acceleration. the Dennis Lancet Ill put up another excellent performance in taking only 21-ls secs. to reach a speed of 30 m.p.h. from a standing start, passing through the gears. Incidentally, this was the only occasion on which we were made aware of the existence of a gearbox, the somewhat hasty changes, without the normal waiting period, being responsible. We mention this particularly because the change up and down can be made without a vestige of noise, if one be not out to clip off a second. The overdrive, which is pre-selective, can be engaged or disengaged without a close observer even being aware of the fact

During the whole test we covered 74 miles and we can best' describe the experience as comparable with that of private-car motoring. At all road speeds up to the governed maximum of 48-50 m.p.h., which was held on several occasions, passenger comfort is excellent, not only from the point of view of body stability, but from the fact that extraordinary smoothness is apparent from the engine right throughout the transmission line.

Leading dimensions of the chassis are as follow:

Wheelbase, 17 'ft. 5, ins.; overall length, 26 ft. 10i ins.; dash to end of frame, 22 ft. 4 5-16 ins.; width of frame, front 3 ft. 2i ins., rear 3 ff. 11 5-64 ins.; clearance forward of rear axle, 12i ins.; under rear axle, 74: ins.

It. is our opinion that this new Dennis, chassis is a most worthy addition to the many other excellent examples of road vehicle which have emanated from the works of this well-known maker.

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