Morris Commercial "Long Stroke Gives a Lively Performance
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WHEN the Morris-Commercial 5-ton 41-litre 75 b.h.p. oilengined chassis was first announced in "The Commercial Motor" on April 16 -last, mention was made of a new four-cylindered petrol engine, which would be interchangeable with the compressionignition unit first fitted. At that time, the initial batch of the experimental petrol engines was passing through
• rigorous road trials, and it was only a week ago that "The Commercial Motor" was able to make the first test of the production engine.
The new 3.77-litre petrol engine is powerful for its capacity and, on the road, provided rapid acceleration from rest, and a good all-round performance. As a result of the ample 'power output, a high rear-axle ratio of 6.714 to 1 has been adopted. With the vehicle working at normal speeds. this affords the advantage of relatively fewer engine revolutions per mile, thus prolonging the effective life of the power unit, and showing an economy in fuel consumption.
Although the unit resembles its predecessor in outward appearance, the stroke has been increased to 120 mm., raising the compression ratio to 6 to 1 The bore diameter of 100 mm. is retained, The power curve shows that 80 b.h.p. is developed at 3,000 r.p.m., and torque of 179 lb.-ft. is available at 1,750 r.p.m.
Thus, the output is slightly higher than that of t h e compression ignition engine, which was apparent during my test. This may 134 partly be attributed to the Solex downdraught carburetter, which gives lively acceleration with economy.
Crankcase and cylinder block are an integral casting, and the interior of the block is accessible for the removal of sludge or scale. Three main bearings are employed, and following modern practice, they are prefinished. Both the main and connecting-rod big-end bearings have half-steel shells, lined with white metal.
Like other Morris-Commercial designs, the engine is a side-valve unit, the valves operating in detachable cast-iron guides. All the valves are interchangeable. The tappets
have been lengthened to afford a larger bearing surface, and provide long, trouble-free operation.
The engine suspension, transmission and frame are identical ',with those of the oil-engined chassis. Four-point rubber suspension is provided, the front of the engine being carried by brackets on the timingease cover, and the rear on brackets from each side of the clutch housing.
The single-dry-plate Clutch is fitted with a spring-drive centre plate, which provides ease of operation and smoothness Of action. Of unit construction with the engine and clutch, the four-speed gearbox is made of cast iron. A sturdy third ratio is provided by using constant-mesh doublehelical gears, and a dog engagement unit. Drive from the gearbox to the axle is transmitted through tubular propeller shafts supported at the centre by a flexibly mounted bearing, which is suspended from a frame, cross-member.
As in previous Morris-Commercial chassis, a split rear-axle casing is employed, the drive being taken through a spiral-bevel unit and fully floating axle shafts. The frame is strengthened at the fore end, and reinforced at the centre by a triangu
lated cross-bracing. Five channelsection cross-members are used to make the frame a rigid structure.
The test chassis, complete with lorry body, spare wheel and full tanks, tipped the scales at 2 tons 13 cwt., which was increased to nearly 84tons with the addition of the payload, driver and observer. The payload of 5 tons 12 cwt. compares closely with that carried by the oil-engined chassis described in' road-test report No. 343, published on May 14.
My main object was to draw a comparison between the performances of the petrol and oil-engined chassis. Unfortunately, the earlier test. was made with a 6.57 to I axle ratio, as opposed to 6.714 to 1 used for the petrol-engined machine. The latter ratio is now standardized for both vehicles, In drawing a comparison, a small allowance must, therefore, be made in the acceleration and hill-climbing results of the oiler. '
Immediately on starting from the works, I was aware of the harsh induction roar of the engine, and it was only towards the end of the day that my ears became more accustomed to the noise. The carburetter choke control was used sparingly for the first few minutes of our journey, and after five minutes, the engine got more into stride and began to exhibit liiTeliness. In acceleration, the Morris-Commercial appeared at least equal to vehicles of a similar class, and on level stretches, we increased speed to 45 m.p.h. and a hove.
Acceleration trials were made over the same stretch of the Chester road, as was used on the earlier test. A check on the radiator water showed its temperature to be 155 degrees F., an atmospheric temperature of 50 degrees F. being recorded.
Starting from rest in second gear, a change to third speed was made at 16 m.p.h., and to top gear at 28 m.p.h. Using third gear to reach 30 m.p.h. proved to be of no advantage when compared with later results. Employing all three ratios, 20 m.p.h. was reached in 12.0 secs and 30 m.p.h. in 26.1 secs. This shows the petrol-engined chassis to be the faster by 4.2 secs. at 20 m.p.h. and 14.2 secs. at 30 m.p.h_
In top gear, a heavy vibration set in at 8-10 m.p.h. Average of times recorded between 10 m.p.h. and 20 m.p.h. showed a result of 16.5 secs., and between 10 m.p.h. and 30 m.p.h., 36.2 secs. This shows a reduction of 3.2 secs. at 20 m.p.h., and 6.1 secs. at 30 m.p.h. over the figures obtained
during the oil-engine test. As mentioned before, adjustments must be made for the lower axle ratio employed in the petrol-engined chassis.
After connecting the small tank into the system, the fuel-consumption trials were started, again using the same route as before. To recapitulate, the course is planned over a normal main road, avoiding possibilities of enforced stops, and including average gradients. Fortunately, little traffic was encountered, and excluding slowing down to negotiate two roundabouts, no other occasion demanded the use of brakes or gears.
The course was covered at good speed, an average of 28.6 m.p.h. being maintained, comparing well with the average of 28.7 m.p.h. on the previous test. Calculations at the end of the route showed a consumption equivalent to 11.27 m.p.g., which is 7.13 m.p.g. less than that obtained with the oil engine.
During a second circuit, a short stop was made at the end of each mile to represent conditions encountered in local haulage. This reduced the fuel-consumption rate to 9.6 m.p.g. I had taken over the controls for this trial and enjoyed the rapid acceleration and general easy handling of the vehicle.
The steering was light, gear lever well to hand, driving visibility excellent, and the brakes were progressive in action and equal to all emergencies. Flexibility of the power unit may be judged by the high average speed for this run, which, after deducting standing time, worked out to 24 m.p.h.
After lunch, I drove through Birmingham to Romsey Hill. Gear changing was remarkably simple, and swift or slow movements of the selector lever failed to provoke protest from the gearbox.
Romsey Hill is approximately a mile long and of an average gradient of 1 in 12, the steepest section being 1 in 7. During the earlier test with the oil engine it was necessary to _use bottom gear, and the time recorded for the trial was 6 mins. 38 secs. I was assured by the works tester that the petrol-engined chassis would show great improvement on the time and would scale the hill in second gear.
Bringing the stop-watch into action, we started in second gear and, within a few seconds, third gear was engaged. The Morris-Commercial roared up the hill in fine style, but, meeting the steeper inclines, second gear had to be used. This change was made rather late, and the engine developed heavy detonation which enforced a rapid change to bottom gear. This, and the time recorded (5 mins. 23 secs.), caused comment from the driver.
I decided, therefore, to make, a second attempt and, changing gear at a higher road speed, managed to scale the hill in 5 mins. 8 secs. with. out using low gear. This timing represents lf mins, improvement on the oil-engine performance, proving the petrol-engined chassis to be eminently suited to fast haulage in hilly areas. • Radiator temperatures of 157 degrees F. at the foot of the hill and 193 degrees F. at the finish of the trial were recorded. Ambient temperature at the time was 41 degrees F. Because of the low atmospheric temperature it is possible that the cooling water would have reached boiling point on a hot summer's day, when the temperature would be in the seventies.
In descending the hill, the brakes Were used to check the road speed to 20 m.p.h., and the drums were still showing signs of heating when the brake tests were made. Stopping distances of 20 ft. from 20 m.p.h. and 45 ft. from 30 m.p.h. confirmed the results of the previous test.
As an encore to the hill-climb, we scaled Mucklow Hill on the return journey to the works. This was surmounted in second gear, with ease, at 12 m.p.h., being the lowest road speed. The Morris -Commercial proved its hill-climbing ability on Mucklow by passing all other goods traffic in sight, a feat which obviously surprised some of the drivers of other vehicles on the hill
Engine lubricating-oil temperatures taken during normal operation gave readings of 110-112 degrees F., whilst the radiator water remained fairly consistently. between 150 and 157 degrees F. Cab heating could be controlled between 45 and 75 degrees F. with adjustment to the window opening, and I found no unpleasant draughts at any time.
. At the end of 72 miles, which was the total distance for the day, I decided that the vehicle was well suited for fast hauls and that its general all-round performance was well up to standard.