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Six-cylindered Oil Engine in Guy Otter Gives Better Performance in Hilly Areas: Alteration in Transmission Improves Acceleration
By Laurence J. Cotton
HERMITAGE HILL, Bridgnorth, is a notable test climb for commercial vehicles in the Midlands, and it was here that the Perkins-engined Guy Otter cut three-quarters of a minute off the timed section by covering the observed distance in 3 mins. 36 secs. Carrying a full load, it completed a 48-mile out-and-return course with a consumption rate of 17 m.p.g.
This vehicle is additional to the present Otter range, which includes a petrol-engined tractor and shortand long-wheelbase chassis, and similar models equipped with the Gardner 4LK power unit. The P6 has higher first and reverse gears than the other models and has constant-mesh gears for the second and third ratios.
As the manufacturer of the gearbox, Guy Motors, Ltd., has selected closer ratios which are best suited to the engine output. A variation in transmission ratios is also afforded by a choice of three Eaton two-speed axles, the standard unit fitted into the test vehicle having ratios of 5.83 and 8.11 to 1.
In appearance there is nothing to distinguish the P6 from the others, because the compactness of the six-cylindered engine avoids the need for altering the cab, and the cold-air intake, with built-in louvres and ducts adjacent to the radiator, is retained. The normal-rating power unit is employed, having a maximum torque of 184 lb.-ft. and developing 70 b.h.p. at 2,200 r.p.m. From my B4 experience of the 'chassis, I arri4"Stire it will not be necessary to improve performance by fitting, the highrated engine, which would be more expensive and require heavier transmission components.
Engine vibration is isolated from the frame by rubber pads at the front and a circular mounting encaSed in rubber at the rear of the gearbox, the front flange of the gearbox being arranged for attachment as a unit with the engine and clutch. The case and the internal layout of the gearbox are unaltered, but the addition of constant mesh to second gear ratio and changing the bottom gear to 5.52 to 1 have increased the pleasure of driving.
Gears for all Conditions
The combination of the wellplanned gearbox and two-speed axle affords a selection of ratios for all conditions of load or territory. When driving with the maximum advocated load, according to the tyre rating, I found the best performance in accelerating from rest to be given by using the selection of axle and gearbox ratios as though a five-speed gearbox were fitted, but there were many occasions during the 90-mile test when the half-steps afforded livelier and more economical, performance.
For normal conditions, the fohrspeed gearbox and two-speed axle are, in my opinion, preferable to a five-speed gearbox, and fixed-ratio axle, because the latter combination requires a heavier transmission. In the Otter, a five-speed unit would necessitate a new design of case and shafts and modification to the frame.
Good Cruising Speed
Equipped with a timber drop-sided body, the test vehicle weighed under 3 tons, so it was driven hard during the trials, observing a 35 m.p.h. maximum speed during the consumption tests, and in a fast-cruising trial [found it could maintain 40 m.p.h. without great effort.
After adding the load, checking the tyre pressures (the standard equipment is 34 by 7/7.50-20 ins.) and fitting a fuel-consumption test lank, the vehicle was driven from the Wolverhampton works to Old Hill, Tattenhall, which is a freak climb of approximately 250 yds., where a maximum gradient of 1 in 5 was recorded.
As this hill is within a short distance of Wolverhampton, the friction and oil-churning losses were high, but the gradient Was climbed in comfort in first gear, using high ratio in the axle, and a stop-start test .Was" made Without .dtScoMfort, -During a repeat test,' with bettertimed gear. changes, the second-gear low ratio was employed without slackening engine speed as the. Otter roared over the crest. This performance was achieved, with a gross running weight of almost 9 tons, because extra observers were carried to witness the climb.
I was perched on the bonnet during the second test, and although I would not recommend this position for general travel, I did at least find that the noise and heat-insulating material painted on the underside of the bonnet is most effective. Relatively little noise penetrates to the cab. The engine mounting arrangements, which free the frame from oscillation at low speed; are also excellent.
Part of my driving period was from Wolverhampton to Watling Street, where the short performance tests were conducted. First I noted the light steering, which has a largediameter wheel and a cam-androller box, and is free from road shock or tendency to oversteer. The electrically operated gear change for the axle is simple to use and by judiciously releasing the accelerator pedal after moving the axle control, the gear change can be made. without depressing the clutch pedal.
Acceleration tests were made first with the low ratio engaged in the axle and it took 27.9 secs. to reach 30. m.p.h. , Afterwards the alternative axle ratio was employed and 3-.9 secs longer was reqtitiect'
reach the` same speed. This indicates that for normal acceleration from rest it is preferable to employ the low ratio in the axle, and use the higher ratio as a fifth gear or overdrive. This was confirmed by a subsequent trial, using first-low with further changes to second-high, third-tow, third-high and fourth-high gears, when acceleration was slower.
Again, as might be expected, the best performance in direct drive from 10-30 m.p.h. was with the lower ratio of the axle in use. The run took 5 secs. longer (31.7 secs.) when employing the higher gear.
decided to add further mileage
before testing the brakes and drove to a point on Watling Street where normally start the consumption trials of vehicles built in the Mid
lands. This 24-mile course began on the outskirts of Gailey and followed Watling Street to Crackley Bank, where we forked back on the Shifnal road through the town towards Bridgnorth.
There is rather more than an average number of road undulations on this route, but apart from one gradient where third gear was employed, and a traffic delay in shifnat, there was no further need for gear changing, the rest being accomplished by the two-speed axle. The course is favourable on the outward run and the addition of 10.65 pints of fuel after completing the 24 miles indicated a consumption
rate of about 18 m.p.g. , Before resuming the fuel tests, I decided to attack Hermitage Hill. Although the vehicle climbed in second and third gears for over 3+ mins., there was only a 7-degree rise in radiator top-tank temperature (from 142 to 149 degrees F.). This was a true indication of watertemperature rise, because no thermostat was fitted. Day temperature at the time was 51 degrees F., and was constant during the trials.
I have already mentioned that the Otter made a spirited climb and is a vehicle I would recommend for use in hilly areas. The alternative axle wittL lower ratios would be required only for a tractor unit.
Returning to the scene of the fuel tests, thetank was refilled and the first long hilt required indirect gear for almost two minutes. More use of the lower ratio in the axle was needed, but a traffic-free run through Shifnal saved valuable seconds and the return trip was made in half a minute less than the outward journey: Slightly more fuel was used but over the 48-mile course the 136 consumption rate worked out to 16.93 m.p.g. at 26.3 m.p.h. average speed. Full-load was carried for the entire distance and the course was severe, but the consumption rate recorded is approximately average for an oil-engined lorry of the 5-6ton class.
Operators usually find that their vehicles show improvement on the consumption figures derived from 'The Commercial Motor" trials, because often a part-load is carried or empty mileage is run in service, whereas a full payload is carried during any one-day test. A further point is that the test vehicles are new and the initial friction might be high.
From previous experience of Otter chassis I have learnt that it has good deceleration, the brake system employing a Clayton Dewandre servo with Lockheed operation for the Girling leading-shoe units. The system provides ample assistance and the hand brake held the loaded vehicle stationary on Old Hill without any great effort on the lever.
The -descent of Hermitage Hill was made without apparent loss of brake efficiency and during the subsequent emergency applications, on level ground, the vehicle was brought to rest in 52 ft. from 30 m.p.h., corresponding to a retardation of 0.58 g. A one-day general test cannot provide conclusive evidence of braking performance, but the results indicated a good average.
I returned the Otter to the Wolverhampton works highly satisfied with its general behaviour. Bearing the hallmark of Guy dependability, it should be a popular model with A-, Bor C-licensees, or in its other guise as a small bus.
The latest Otter cab gives a much greater range of vision than the earlier type, because the windscreen has a minimum depth of 2 ft. 1 in., and narrow corner and central pillars prevent blind spots. More space is provided in the interior and the cab is constructed on a metal base with wooden vertical pillars covered with light-alloy panels. The seat is adjustable fore and aft and slides on an inclined plane.