DENNIS produces a
Page 64
Page 65
Page 66
If you've noticed an error in this article please click here to report it so we can fix it.
2-TON CHASSIS
A Fine Model of Robust Construction, Excellent Design and Moderate Price.
FIRST impiessions are not always true, but .12 we are certain that they are so in the case of those which we received when we examined the entirely new 2-ton B-type chassis produced by Dennis Bros., Ltd., Guildford.
The first characteristic which appealed to us was its remarkable robustness for its load capacity ; what next appealed was its clean design and finish, and, later, when we went more thoroughly into the details of the construction, we were impressed by the attention which had obviously been given to easing the work of inspection and maintenance.
This new chassis is no modification of an existing type. It is new throughout, embodying a powerful four-cylindered engine of 85 rem. bore and 120 mm. stroke, and a crankshaft with bearings 21 ins, in diameter. The overhead valves are operated by rockers and the engine develops up to 42 b.h.p. at 2,000 r.p.m.
The new four-speed gearbox has right-hand change, unusually large pinions and particularly stiff shafts, and the new back axle is of the pot type with overhead worm gearing and full-floating shafts.
Commendation must also be given to the brakes, Both foot and hand operate through internal-expanding shoes in rear-wheel drums 17 ins, in diameter, and the foot brake is actuated through a Dewandre vacuum servo.
The method of taking stresses due to the drive and braking is by carrying -the forward end of the long torque tube in a spherical housing securely bolted to the rear of the gearbox. This is a very satisfactory' arrangement, and is one not usually found on a chassis of this capacity.
Before going farther into the details of the design we will give the main chassis dimensions, etc.:—Length overall, 18 ft. 3/ ins.; width overall, 6 ft. 7 ins.; dash to end of frame, 14 ft. 4i ins.; dash to centre of rear axle, 9 ft. Si ins.; frame width, 2 ft. 8 ins.; frame height laden (with 36-in. by 8-in. pneumatics), 2 ft. 41 ins.; frame height laden with 32-in. by 6-in. pneumatics (twins at the rear), 2 ft. 21 ins.; wheelbase, 12 ft.; track, 5 ft. 11 in.; clearance under rear axle, 111 ins.; approximate turning circle, 51 ft.; chassis weight, 371 cwt.; allowance for body, 15 cwt ; allowance for driver and spare wheel, 31 cwt.; useful load, 2 tons; gross weight, 4 tons 16 cwt. It Is equipped with 32-in, by 6-in. tyres (twins at the rear), spare wheel and tyre, 'Lucas electric lighting with
five lamps, electric horn, combined mileometer and speedonoiter, driving mirror and tool outfit.'
Reverting now to the enw'ine, the four cylinders are cast en bloc with the upper half of the crankcase, whilst the head, which is of efficient design, is detachable in one piece. The va/ves are all at one side, and the push rods operating the rockers are entirely enclosed. The rockers are carried by floating bushes on a tubular fulcrum shaft, through which lubricating oil passes under pressure. The shaft with its rockers can be removed completely by unscrewing one nut on each of the three standards supporting it. Each rocker has, pressed into it, a hardenedsteel housing for a steel ball which has a fiat ground at one point, this flat contacting with the valve stem; at the other end of each rocker is .ball-ended adjusting set-screw. Not only are the push-rods entirely enclosed but the whole of the gear is protected by a neat cover held -down by large .milled nuts.
Circulation of the lubricating oil is effected by a '"'ear pump driven from the camshaft, the oil passing, as ni-e title d • before. through the hollow camshaft to the Mani. bearlugs ; the crankshaft is drilled tri fake the oil to
the big-ends. A convenient filler and screw-topped dipstick ,are provided at the near side.
A centrifugal pump forces the coaling water through a single entry at the bottom of the cylinder jackets at the Off side, and it issues from a single exit at the near side of the head.
ignition is effected by a Simms SF4 magneto with variable timing. This is mounted at the near side of the timing case, whilst the water pump is mounted in front of the ease. Helical spur gears are employed for the timing. Adjustment for end-play on the camshaft can be effected by a hardened stop mounted on the timing case and provided with a simple lock ing device.
The single exhaust manifold is bolted to the top of the Ricardo divided-type inlet manifold to form a hot spot, and the exhaust is carried forward.
To assist in timing the engine, the top dead centre is marked on the flywheel and can be viewed by removing a plug on the bell housing, there being a registering arrow On the housing. The top dead centre is also shown by a. V cut on. 'the outer flange of •• -the fan-belt pulley, this
being brought to coincide with a lug formed on the front engine-suspension bracket.
Petrol is fed to the carburetter through a 9-gallon tank mounted on the dash.
The engine and gearbox form a unit, and the enclosed clutch is of the external-cone pattern faced with fabric, The adjustment is extremely simple, and a clutch stop is provided, this stop acting upon a steel ring bolted to the die-east aluminium cone. An improved method of securing the fabric has been adopted. One-eighth-inch holes are drilled and only the cone is countersunk, the material being pulled into the countersinks by aluminium rivets, which are held on the inside by snapheads bearing against steel washers.
Compactness combined with accessibility is a prominent point of the gearbox, in which the gear ratios are as follow :—Top, direct ; third, 1,75 to 1; second, 2.76 to 1 ; first, 6.36 to 1.
One of our illustrations shows the top cover removed and the side cover withdrawn together with' the selector-fork and selector-locking mechanism. To remove the selectors it will be l'ound that it is necessary only to undo the nuts of the cover and the two bolts holding the selector lock. Incidentally, this lock is of an unusually simple and practicable type which replaces the calliper pattern so often employed ; its details' can be seen from one of our illustrations. It is quite impossible to mesh two sets of gears at the same time, Ball and roller bearings are utilized throughout the box. The splines on the shafts and pinions are most carefully ground and fitted so closely that it is practically impossible for small pieces of metal to embed themselves in a shaft. The chrome-nickel-steel gears are' of five pitch. At the near side of the ,hox is a small plate which can be removed to permit the• fittinr,' of a tyre' pump. If required the gearbox pinions can he removed from the rear end.
We have already referred tothe propeller-shaft tube. This is of large diameter and is divided in the centre to
house a roller . bearing for the .shaft. Tubular radinS stays are mounted between the tube and the ends of the rear axle. The -standardratio of the worm gearing in the back axle is 71 to 1. The top coVer can easily be removed, together with the differential, without taking down the axle or removing the 'wheels; it is, of course, necessary to withdraw the: axle'shafts before this operation can be carried out, but this can be done without jacking up the chassis: An oil filler, which also acts as a level, is carried at the back. Of the -axle casing.
The rear wheels are mounted on taper-roller bearings, and the detachable steel-disc wheels are held in position by eight studs having spherically seated nuts.
Adjustment of the brakes can easily be effected by large nuts placed in an accessible position at the rear of each rod. The brake shoes have complete eyes at their
pivoting cads, and the drums can be removed' to 'inspect the shoes and facings without interfering with the wheel hubs.
Ball-thrust bearings are mounted above the swivels of the front axle, which is an 11-section stamping of special steel, heat treated. The front wheels also run on taperroller bearings.
A worm-and-wheel steering gear is carried in an oil-tight case supported direct from the frame, and provision is made to permit remeshing the wheel in several new positions as wear occurs.
The steering rods are fitted with spring-loaded ball joints, each of which is adjustable for wear and carries a pressure-gun lubricating nipple.
We have not yet referred to the sturdy frame. This is of channel-section pressed steel, 01 ins, deep.
Much use is made in this chassis of spherical bushes for the brake cross-shafts, and the change-speed-lever shaft, thus avoiding any risk of binding through frame flexion.
At first it is rather puzzling to realize how a spherical bush can be inserted into an undivided spherical housing. This is effeeted by slotting the housing at two opposite points, inserting the bush at right angles and turning it around into the correct position.
The matter of suspension has also received careful attention. The springs are long and of chrome-vanadium steel. Those at the front are particularly flexible to prevent the disagreeable vibration which so often occurs at this part of a,: vehicle.
The petrol consumption is approximately one gallon to 16-17 miles, and the oil consumption a gallon to 1,000 miles.
All wearing parts, such as spring shackles and bolts, are provided with pressure-gun lubricators.