Greater Power: Less Fuel
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By Laurence J. Cotton,
Y employing a 100 b.h.p.
overhead-valve petrol engine in "place of the former fourcylindered side-valve unit, the general performance of the MorrisCommercial 5-tonner is improved without increasing fuel consumption. This was discovered in a road lest with consumption trials over the same course, when the six-cylindered engine yielded a m.p.g. improvement despite a higher average speed.
Apart from the introduction of the new engine and slightly higher indirect ratios in the gearbox, the Morris-Commercial 5-tan forwardcontrol model is basically unchanged. The engine and gearbox are accommodated within the former cab, thus leaving space for a 17-ft. body on the 150-in.-wheelbase chassis.
Straightforward Design The new power unit is conventional in design, having a monobloc crankcase cylinder block casting with four-bearing crankshaft retained in replaceable-shell, white-metallined bearings. A similar type of bearing is employed for the connecting rods.
A duplex roller chain operates the camshaft, with push-rods to the overhead-valve rocker gear. Lubrication equipment includes a submerged gear pump driven from the B8 camshaft and fitted with a floating oil-strainer intake. A full-flow filter with replaceable cartridge element is also provided.
There has been a torque increase of 23 lb.-ft. to 202 lb.-ft., but this higher output is well within the capacity of the former 11-in.diameter clutch, which is retained. As the maximum torque is delivered at a lower speed, now 1,800 r.p.m., the pulling characteristics are improved and less gear changing is required. The close-ratio gearbox, with an overall spread of 5.83, has also helped the acceleration and hillclimbing performance. Third is a constant-mesh double-helical gear with dog-clutch engagement.
As in the Morris-Commercial 2-5ton range, a split fully floating rear axle having a spiral-bevel final drive is used A home model having an unassisted Lockheed brake system and 11-in.-diameter master cylinder of l-&-in. stroke was tested. The export version is equipped with a Hydrovac boost e r. With the unassisted system the retardation is relative to the pedal pressure and on test 170 lb. pressure was sufficient to cause rear-wheel locking. The standard cab, weighing 5 cwt., is a composite structure with controlled ventilation and rear-hinged doors ahead of the axle. Grab rails are provided. The combination of forward drive and deep windscreens makes for good visibility when shunting in a restricted space.
With a 16-ft. body having 18-in. drop sides, the vehicle weighed 21 tons unladen and a 51-ton load was• added to bring the total to 81 tons, which is the advocated gross maximum weight with 34 x 7-in. tyres. This running weight was comparable to that of the former test, but as the new power unit weighs about 2 cwt. more than its predecessor, the payload was reduced accordingly.
The good turning circle, which measured slightly under 53 ft. on both locks, was helpful in negotiating a difficult turn in the works. After fitting the brake test equipment, a fifth wheel for accurate measurement of speed, and a fuel test tank, the lorry was headed towards Stonebridge for the first stage of the trials.
Induction Noise I soon found that this was to be a. lively day's work, especially when the works representative, who took first spell at the wheel, accelerated to overtake cars and coaches at 45 m.p.h. and more. I have previously commented on the harsh induction roar of the MorrisCommercial 5 tonner and this criticism applies to the latest version, although the air filter is mounted below the engine cover.
At Stonebridge the fuel system was changed to draw petrol from the test tank and 1 took control for the first consumption trial, which followed the main road to Warwick, passing through Kenilworth. Top gear performance is excellent and, apart from starting from rest and the use of third gear in the Kenilworth traffic, there was no need to employ the indirect ratios.
On the.outward run, 10.73 miles were covered before a gallon of petrol was exhausted and with less traffic on the return trip, the fuel lasted for 12.518 miles. The mean of the two runs worked out to
11.6 m.p.g. and, deducting standing time, the average speed was precisely 30 m.p.h. In an earlier test with the four-cylindered engine, the fuel return was 11.27 m.p.g. at 28.6 m.p.h.
The short performance tests were conducted on the Warwick-Banbury road and here the increased liveliness was shown by accelerating from rest to 30 m.p.h. in 19.8 sec., compared with the former 26.1 sec.
Improvement was again noticeable in the top-gear trials from 10 m.p.h., in which the engine accelerated more smoothly and with only slight pinking on a commercial grade of fuel. The acceleration was generally better, occupying 12.5 sec. to 20 m.p.h. and 27.5 sec. to 30 m.p.h., against 16.5 sec. and 36.2 sec. respectively in the previous test made with the side-valve engine.
As there has been no change in the braking system, the retardation rate is unchanged, although some difference was noted because the Webley marker is more accurate than former methods of measuring stopping distance. Having recently driven a five-year-old Morris-Commercial I was accustomed to the braking characteristics, but drivers new to a straightforward hydraulic system, without the vacuum assistance, might at first complain of a " heavy " pedal.
Rear Wheels Lacked
Retardation, as I said earlier, is proportional to manual effort and with a pedal pressure of about 170 lb. the rear wheels locked and stopping distances ranging from 54-68 ft. were obtained when stopping from 30 m.p.h. Such distances are good averages for a 5-ton goods chassis, especially if no great loss of efficiency occurs in the subsequent life of the vehicle. My experience with the five-year-old Morris-Commercial, which had over 80,000 miles to its credit, indicated no serious deterioration.
I have seen several commercial vehicles in difficulties on Edge Hill, between Stratford and Banbury, and decided that this would be a fair test for the Morris-Commercial. It climbed the half-mile gradient comfortably in second gear from a standing start until reaching the 1-in6 section near the brow, where brief use of low gear was required. There was ample reserve power for a stopstart test at this point in the second trial.
I had driven the lorry hard on the way to the hill-climb, raising the water and oil temperatures to 185° F. and 168° F. respectively, with a moderate day temperature of 53° F.
and practically no breeze. I expected the water to boil on the hill, but was mildly surprised to find that it remained at a constant temperature in the first test and then cooled off slightly on the second attempt. This indicated ample air flow from the four-blade fan at high engine speed.
Although spvering only 80 miles in this one-day test, I was satisfied that the new engine will provide the operator with a vehicle of higher performance without addiqg to fuel costs. In more undulating parts of the country the use of a lower ratio for hill-climbing might effect more marked economy than the results of my trials.