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Latest Version of Commer Forward-control 5-tonner Has Perkins Six 354 Diesel Engine : Highly Satisfactory Road Performance Results, and Braking Matches Other Improvements: Cab Comfort High and Engine
Noise Low
by John F. Moon, A.M.I.R.T.E.
IT is over .131, years since Commer Cars, Ltd., released to an unsuspecting world details of their then revolutionary 5and 7-ton forward-control goods chassis, one of the most novel design features of which was the installation of the power unit beneath the .cab seats, giving what was at that time unrivalled cab access.
Over the years the appearance of the Commer 5-tonner has not changed greatly, but, nevertheless, some really important chassis improvements have been effected, and the latest Commer diesel-engined 5-tonner has by far the best performance of any vehicle which has been produced in this class by Commers. with good fuel economy, acceleration, hill-climbing and braking performances, plus a very satisfactory degree of handling and general cab comfort.
The current Comrner 5-tonner, an example of which I tested recently, was introduced on May 5, 1961, and described in The Commercial Motor of that date. It differs from its immediate predecessor—introduced about three years . ago—in having the Perkins Six 354 diesel as the standard diesel-engine option, the earlier model having the Perkins C.305 unit, which developed 79.5 b.h.p. (net) at 2,400 r.p.m. and 208 lb.-ft. torque at 1,300 r.p.m. This compares with the Six 354's outputs of 103 b.h.p. at 2,600 r.p.m. and 254 lb.-ft. at 1,450 r.p.m. The overall improvement in performance occasioned by the difference between these two engines should not be hard to imagine!
When Commer's announced the option of the Six 354 in their 5-ton forward-control chassis, it became available in their 4and 6-ton forward-control models, in the Superpoise 5and 6-tonners and in the Karrier Gamecock 3-4tonner also. In the Superpoise normal-control chassis the
Perkins engine is used in conventional vertical form, but in the Commer and Karrier forward-control chassis a modified engine design is employed, the modifications being to allow the unit to be mounted at an angle of 66 deg. to the vertical and consisting principally of a new sump, modified manifolds and slightly different crankcaseventilation piping.
The ratings of both versions of the engine as used by Commer are slightly different from the standard Perkins ratings in that the governed speed is cut down by 200 r.p.m. from the normal 2,800 r.p.m., which reduces the net output by 2 b.h.p. This de-rating has been carried out principally to reduce the maximum road speed. although even so this is still in excess of 60 m.p.h.—more than sufficient for normal operation in Britain.
A Commer 102.5 b.h.p. (net) petrol engine is the optional power unit in the forward-control 57tonner, and when this is specified a four-speed constant-mesh gearbox is employed. With diesel-engined chassis, however, a fourspeed baulk-ring-synchromesh box is standard, and this can be ordered with an optional fifth overdrive ratio, as fitted to the gearbox of the test vehicle. A five-speed constant-mesh direct-top box is optional for 5and 6tonners.
Similarly, there is a difference in the rear-axle ratios of •the petroland diesel-engined models, although the same basic spiral-bevel axles are used. The petrol version has a 6.57-to-I final drive, giving a theoretical maximum speed of 48.5 m.p.h. in direct top gear, whilst the diesel model has a 5.125-to-1 axle, which gives a theoretical top speed of 53.75 m.p.h. with direct top gear.
A further difference in chassis specification between the petroland diesel-engined models concerns the rear-axle brakes. Girling two-leading-shoe units are employed in both cases, but whereas the slightly slower petrol chassis has 15.25-in. x 4.25-in, equipment, the faster diesel job has • 15.25-in. x 5-in. brakes, effecting an increase in the total frictional area of 44 sq. in.
In other main respects the specifications of the two chassis are virtually identical, the standard wheelbase in each case being 11 ft. 9 in., with a common gross weight rating of 81 tons on the standard 7.50-20 (10-ply) tyres, which rating is increased to 8f tons when the optional 8.25-20 (12-ply) tyres are fitted.
When, as in the case of the test vehicle, the standard Commer 15-ft. 6-in, timber drop-side body is mounted on the chassis, the kerb weight approaches 31 tons, therefore operators wishing to carry a genuine 5-ton payload should specify the larger tyre equipment.
The current version of the Commer forward-control cab was introduced in 1958, and although basically not so very different from the original 1948 design, various important detail improvements have been carried out over the years, including the use of a one-piece curved windscreen and the provision of a separate, adjustable driving seat alongside the two-man passenger seat as opposed to the onepiece bench seat of the original design. A thin felt blanket provides some measure of insulation over the seat box, and as the Perkins Six 354 is a reasonably quiet engine in any case, noise level in the cab is comfortably low, even when running on the governor.
Gravel formed the payload for my test, and 4 tons 14 cwt. of this commodity almost filled the body and brought the gross vehicle weight—less myself and two Commer personnel—to 8 tons 3+ cwt. The weight distribution was such that with the three of us in the cab, all six tyres were more or less equally loaded.
Extremely Good Retardation
Braking tests were carried out first, and a level stretch of concrete road was chosen. Extremely good retardation figures were recorded, with Tapley-meter figures of 88 per cent. from 20 m.p.h. and 76 per cent. from 30 m.p.h. When braking from 30 m.p.h., wheel locking occurred at the offside rear, aggravated by the soft expansion strips in the concrete road surface. These strips caused all the wheels to lock slightly when braking from 20 m.p.h. on one occasion, but another 20 m.p.h. stop was made without any locking at all, and it would be fair to say that the braking system is extremely well balanced and should not be prone to locking, even in emergencies, on normal asphalt surfaces.
Hand-brake efficiency was good, 35 per cent. being recorded on the Tapley meter when using this brake to stop from 20 m.p.h. Nevertheless, this hand-brake performance is not as good as that recorded in our November 7, 1958 issue, when a test report of a Commer forwardcontrol 6-toriner was published. This vehicle had the 4.25in.-wide rear brakes of the current petrol-engined 5-tonner, and although the foot-brake performance was inferior to that of the latest 5-tonner, the hand-brake retardation was nearly 20 per cent. better.
Remarkable standing-start acceleration times were obtained, the 0 to 30 m.p.h. figure being better than that recorded in 1955 with a Superpoise petrol-engined 5-tonner. Second gear was employed when starting off during these tests, a speed of 20 m.p.h. being obtainable in this ratio, whilst third gear was good for 38 m.p.h.
By comparison, the direct-drive acceleration performance seemed rather dead, but, nevertheless, the figures obtained are good and show a fair degree of consistency in the 10m.p.h. steps between 10 and 40 m.p.h. Because of the relatively high rear-axle gearing, the slight transmission roughness that was noted when accelerating at low road speed was forgivable and, once past 13 m.p.h., both engine and transmission behaved smoothly.
Five sets of fuel-consumption figures were taken with the 5-tonner, the first being over the narrow undulating road between Dunstable and Tring which was covered in both directions to give a total distance of 18 miles. Despite the unfavourable road conditions, the course was completed at an average speed of 29.6 mph., and the overdrive ratio was used for a total • time of 241 minutes out of an overall running time of 36 minutes 23 seconds, this alone giving an indication of the severity of some of the hills encountered. In view of the high average speed and the
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nature of the route, the resulting overall consumption rate of 17.1 m.p.g. is particularly commendable.
Following this "country "-route test, two runs were made over the relatively level stretch of A6 between Luton and Harpenden, one using overdrive wherever possible and the other treating the Cornmer as a standard vehicle without overdrive. There was only 0.1 m.p.h. difference between the average speed on both runs, but a difference of 1.9 m.p.g. in consumption rate, showing the overdrive ratio to effect an 11 per cent. improvement in consumption under such conditions.
The remaining two fuel tests were made over a 7.3-mile out-and-return length of motorway, and here again one run was made using overdrive and the other without, continuous ftill throttle being employed on both occasions, whereas the other runs had been made observing a selfimposed speed limit of 33 m.p.h.
The economy gain given by the overdrive ratio 'dropped to a little over five per cent. on the motorway, and it is significant also that the average speed when not using the overdrive was higher than when using it, this being caused by the overall gearing with overdrive in use (4.225 to 1)
being too high for speeds in excess of 60 m.p.h., whereas when running in direct drive a speed of 64.5 m.p.h. was timed over one stretch, at which pace the speedometer needle was "well off the clock." On the " overdrive " test this ratio was used for seven minutes out of a total running time of eight and a half minutes.
All five fuel-consumption results showed that very good economy can be obtained under a variety of operating conditions, and that even without the optional overdrive ratio fuel costs should not be high with this Commer. The time-load-mileage factors calculated from the motorway runs are exceptional for a vehicle of this weight, and give a measure of the high-speed economy given by the Perkins Six 354 engine.
Gradient-performance tests were conducted on Bison Hill. a 4-mile climb with an average grade of 1 in 104. The tests were made in an ambient temperature of 68'.F., but because of the shape of the radiator-filler neck, it was impossible to take direct readings of the coolant temperature before and after the non-stop climb and the only guide that couldbe obtained as to water temperature was that given by the instrument-panel temperature gauge.
This temperature was approximately 160°F. before the climb and a very lively ascent occupying only three rninutcs.caused this temperature to rise by about 25"F.. by which time the thermostat should have been fully open so that the temperature would, in all probability, have started to drop again had the climb been longer. In any case, I think it is fairly safe to say that the 4*-gal. cooling system is entirely adequate—certainly for British use— whilst there is a higher-capacity radiator for export chassis.
At no time during the climb did the road speed drop below 9 m.p.h., and the lowest ratio employed was second, this being engaged for 1 minute 21 seconds. While in this ratio the engine pulled extremely well at fairly low revs, and no exhaust smoking was observed, although occasionally it was possible to see slight hazing at the exhaust outlet_ To check for fade resistance, I coasted the Commer down the hill in neutral, relying on the footbrake to keep the road speed down to about 20 m.p.h. Towards the bottom of the hill, where the gradient is less severe, I engaged direct drive and applied full throttle .to keep the brakes working.
The descent lasted 2 minutes 28 seconds and at the bottom of the hill a full-pressure stop from 20 _m.p.h. produced a Tapley-meter reading of 64 per cent., showing a reduction through fade of 0.24g.—a creditable performance after so severe a test. There was no noticeable increase in pedal travel and no smoke was coming from the drums.
After only a brief pause to allow the brakes to cool down, I then drove the 5-tonner back up the hill and 59 THE COMMERCIAL MOTOR stopped it on the steepest section, where the gradient is 1 in 6-1. The handbrake held it satisfactorily on this slope, and a smooth getaway was then made using bottom gear and only fractional throttle opening, an excessively optimistic attempt to restart in second gear having failed —but only just. The theoretical bottom-gear grade ability is 1 in 31, and this I can well believe, although whether. the handbrake could hold a laden 5-tonner on this gradient is perhaps open to doubt.
The Commer handled extremely well at all times and should not be found in any way tiring. to drive on long runs, particularly as engine noise is so low. The power unit is very responsive to throttle opening, and the gearbox is pleasant to use, the synchromesh being good although by no means completely unbeatable.
Clutch action is light, whilst the brakes have a satisfyingly firm feel about them without being in any way heavy. The steering is light at all times; and the 18-in.diameter wheel enables a good purchase to be obtained without the risk of the driver knocking his knuckles against the windscreen or door pillar. Castor action is good, and the 5-lonner displayed no inclination to wander.
The cab layout provides a good range of visibility generally, one minor fault being that when the vehicle is standing on a sharply cambered road the driver's eye level above the level 4af the near-side door window, thus
making it difficult to see traffic conditions to the left when stopped at a road junction. The driving seat is adjustable longitudinally, vertically and, by independent setting of the front and rear vertical adjustments, for rake also. Cab comfort was enhanced by the vehicle's suspension which, although undamped, was entirely satisfactory under widely differing road conditions. Dampers for both front and rear axles are available at extra cost, but should not really be necessary for normal purposes.
In all I was very pleased with this latest Commer tanner, and would emphasize again that, although it may look like previous Commer 5-tonners, its performance is entirely up to date and well above that to be expected from many other British models of this capacity. Although neither I nor the manufacturers would recommend it, it is not hard to imagine this vehicle carrying more than its rated 5-ton payload when placed in service, although fortunately, the engine and brakes should be well able to deal with any such eventuality.
As tested, the Commer diesel 5-tonner with standard drop-side body costs £1,313. the chassis-cab version being listed at £1,198. The petrol drop-sider costs £1,115.