Four New Dennis Three Lorries and a Bus
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IN addition to the new Dennis Condor 12-ton-gross chassis which forms the subject of this week's road-test report (pages 100-103), there will be three other new Dennis chassis at the Commercial Motor Show next month.
Of these, the Hefty maximum-load four-wheeler is a completely new design. The Pax III and the Loline double-deck bus chassis are adaptations of existing types, although the Loline is new to the Dennis range.
The Hefty forward-control chassis has a 15-ft. 6-in, wheelbase, giving a body length of 21 ft. 4 in., and is powered by a new 8.03-litre sixcylindered, direct-injection oil engine. This unit has a bore of 108 mm. and stroke of 146 mm. and develops 120 b.h.p, at 1,800 r.p.m., with a peak torque output of 368 lb.-ti. at 1,100 r.p.m. It carries a 131-in.diameter two-plate dry clutch, and is mounted as a unit with a new six-speed indirect-drive two-shaft gearbox.
' Lightweight Gearbox
This box has forward ratios of 4.267,2.526, 1,72, 1.194, 0.838 arid 0.581 to 1, reverse ratio' being 4.33 to I. It is extremely compact and light, considering its capacity, this being one of the advantages of a two-shaft des'ign.
Input and output shafts rotate m opposite directions, which necessitates reverse-drive spiral-bevel gearing in the rear axle, This axle is a Dennis-built doubles-reduction assembly with an overall ratio of 9.47 to I, which explains the comparatively high low gear of the gearbox. The hub-mounted epicyclie reduction gearing in the axle allows the use of small right-angle-drive and differential gears, which in turn allow a small axle pot to he used and afford good• ground clearance.
This new axle is much lighter than a worm-drive unit of similar capacity, and the half-shaft loadings are lighter. Top gear gives the Hefty a theoretical niaximurn road speed of 39 m.p.h., while the maximum gradient that can be climbed in low gear is 1 in 4.35.
Air-hydraulic braking is used, with Clayton Dewandre and Girting equipment. The wedge-operated brake units are the same size as those employed on the Condor chassis.
The chassis frame is built up from ,-in. pressed-steel channel section; the side members have 3-in, flanges and a maximum depth of 10 in.
The new Dennis standard cab is fitted, and the tyre equipment is 10.00-20 in. (14-ply).
By using lightweight gearbox, rear axle and braking system, every effort has been made to keep the weight of the Hefty down to a minimum. A payload of well over 9 tons should he possible, although no official unladenweight ,figures have yet been published by the makers.
Designed throughout to run at 14 tons gross, the Hefty is built true to its name, and is a promising addition to the Dennis range. .
The Pax 111 forward-control chassis is rated for a gross weight of 10.2 tons, giving a clear 6+-ton payload capacity. The I2-ft. 10+-in, wheelbase model which is to be exhibited at Earls Court has a body length of 18 ft. 31 in.
A Perkins P6 83 b.h.p. oil engine is used in conjunction with a Moss five' speed overdrive top gearbox and a new Dennis spiral-bevel-drive rear axle. The alternative axle ratios are 7.17 to 1 and 6.14 to 1.
Gearbox ratios are 6.55, 3.6, 1.81, I and 0.818 to 1 forward and 5 to 1 reverse. The high-ratio axle gives a maximum road speed of 52 m.p.h., with a gradient ability of 1 in 5.4.
Girling wedge-operated hydraulic brakes are fitted, with 16-in. by 3-in. front-wheel units and 15.25-in. by 4.25-in, assemblies at the rear. A Clayton Dewandre vacuum servo is supplied. The standard type'equipment is 8.25-20 in. (12-ply) and a 12v, electrical system is used.
As with . the Hefty and Condor chassis, the new Dennis cab is fitted as standard, and the flat-tube radiator is mounted integrally with the front dash structure. Three-point rubber mounting is employed. The driver's and mate's seats are particularly easy to reach and all-round visibility is good.
The Dennis Loline low-bridge double-deck bus chassis is based on the Bristol Lodekka chassis, as used extensively by bus companies owned by the British Transport Commissicin. It differs from the Bristol chassis in respect of power unit and gearbox. The Gardner 6LW six-cylindered direct-injection oil engine develops 112 b.h.p. at 1,700 r.p.m. and 358 lb.-ft. torque at 1,300 r.p.m.
• A five-speed version of the inversedrive gearbox used in the Hefty goods chassis is installed. Good use has been made of the offset output shaft which is a feature of this box: the propeller shafts to the rear-axle differential lie close to the off-side chassis-frame member, which normally necessitates mounting the engine at a wide angle to the longitudinal centre line. Because of the drive offset already present in the gearbox, however, the amount of engineasplacement needed is much reduced.
• A standard Bristol-type doublereduction, rear axle with offset differential and cranked casing is used. These features allow the gangway to be kept particularly low. The Loline has an I8-ft. 6-in, wheelbase and is suitable for 30-ft. by 8-ft. bodywork. Body outriggers are built on to the chassis frame to make completed buses semi-integral..
Large air-operated brakes are fitted. All the wheels have 161-in.-diameter drums, and the facing widths at the front and rear are 4+ in. and 74 in.
Anti-roll anchor plates are fitted to the. road springs, and the front axle carries safety stops and telescopic dampers. The front tyres are 11.00.20 in. (14-ply), whilst the dual rear tyres are 9.00-20 in. (12-ply).
An F.24 fire-engine chassis, powered by a Rolls-Royce B.80 petrol engine, will be another exhibit. This has a fully automatic gearbox and two-speed synchromesh auxiliary box.
A scale model of a fire-engine will also be shown; this has bodywork similar to that of the new F.25 chassis. The F.25 is a lightweight, low-cost appliance with a Dodge six..:cylinderecl petrol engine. Other exhibits include an A.V.I ambulance and a Heron mobile shop.