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71 AN OIL-ENGINED
2-TONNER
The Mercedes-Benz Miracle Yields Interesting Performance Figures, is Easily Handled and Shows Marked Economy in Fuel
THE employment of oil engines in lighter+, vehicles than maximum-load four-wheelers and six-wheelers, weighing respectively 12 tons and 19 tons gross, has been awaited by many commercial-motor users.; The DaimlerBenz concern in Mannheim, Germany, with its long experience of this type of engine in big freighters, has been one of the first manufacturers to produce a really light oiler, and we were able to publish full technical details of this model In our issue dated March 22nd this year. The first chassis have now reached this country, and a few days ago we subjected one of them to our standard form of road test.
An interesting point concerning this machine is that its general specification has been prepared upon the advice of Mr. A, W. Gaedertz, general manager, and Mr. S. Stilwell, works manager, of British Mercedes-Benz, Ltd., the marketing concern for this country, which has its offices and works at 111, Grosvenor Itoad, London, S.W.1.
1336 The chassis can be expected, therefore, to suit English conditions, and in trials under full load it is found to do so. It should be stated that it has been designed also to suit the world markets generally, the company having good connections in several distant overseas countries, where the newcomer will be regarded as a 2-tonner. Readers using this size of vehicle will appreciate the importance of its coming within the 21ton unladen-weight category. Not only does this mean a saving on the annual licence fee (132 as against 140), but also it entitles the vehicle to a maximum legal speed of 30 m.p.h., whereas if the weight were over 2-i tons the limit would be 20 m.p.h.
The chassis we tested, with a well-built German cab and drop-side lorry body, turned the scale at just over 2 toris, but there should be no difficulty in keeping the weight within that figure. The vehicle was weighed with a full fuel tank (24 'gallons—sufficient • for 480 miles), which would account for more than 2 cwt.
Although the vehicle tested was quite new, having covered only 100 miles since arriving in this country, it had been fairly well run in before leaving the manufacturer's works. We did not, in this case, effect an engine start from cold, but we have on many occasions started Mercedes-Benz oil engines on winter mornings and have found no difficulty whatever in this respect.
It may be noted that If the Bosch switch key be in the "out" position or be completely removed from the instrument board, the current for the electric starter and heater plugs, as well as for the lights, is cut off, also that the starter button (on the dashboard) does not take effect unless the turn switch of the heater plugs is in the " on " position. The manufacturer of this chassis employs first-class electrical equipment and does not make provision for hand starting.
Restarts that we effected during the day after lengthy halts were accompanied by less exhaust smoke than would be expected, and in the ordinary running the exhaust gases were almost always invisible. For our fuel-consumption test the main tank, which is located under the driver's seat, was filled to the top of the sloping neck, and refilled with careful measurement after an out-and-home journey of 47 miles, this including only one stop. The route selected was fair in every respect, and the reading obtained was 20.325 m.p.g. It is simple for regular operators of this size of vehicle to work out the saving per annum as compared with the fuel figure for petrol-engined motors. and for rough calculations a price of 41d. per gallon can be taken for the fuel oil.
• As one of our illustrations shows, the filler orifice and depth gauge for the fuel tank are conveniently located within the cab to the right of the driver's seat. The fuel feeds by gravity to an A.C. camshaft driven pump which lifts it to a large and accessible Bosch filter mounted on the front of the dash, whence it passes to the Bosch high-pressure injection pump.
Inspection of one of the graphs reproduced with this article reveals a performance as regards 'acceleration in the individual gears and from rest through the range of gears, which is comparable with the acceleration of petrol-engined vehicles of similar capacity. The action of the governor is such as to offer steady pulling at all engine speeds, and the performance is aided by an easy gear change and clutch control. As regards power genei;ally, one notices the comparatively high torque developed by the engine at low speeds. This results in later gear changing when tackling a hill, and, in particular, we noticed the usefulness of the third gear, in which, even on quite steep gradients, the loaded machine pulls satisfactorily down to 11 m.p.h. The governed maximum engine speed of 2,000 r.p.m. gives a top speed of just 41 m.p.h., which is ample.
The power developed at low speeds is still more appreciated on really severe hills. When climbing northward up Brockley Hill, on the Edgware-Elstree road, which has a maxignum gradient of about 1 in 8.5, we were tempted to change from second to first gear, but found that it was better not to do so. This hill, which is 440 yards long, was climbed at an average speed of 9.5 m.p.h. A short hill with a maximum gradient of 1 in 6 was ascended in second and first from rest at an average speed of 7.75 m.p.h. Protracted hill climbing did not cause any material rise in the coolingwater temperature, which, at the conclusion of these tests, was found to be 158 degrees F.
On the 1-in-6 gradient the lorry made an easy restart in first gear, but could not quite do so in second gear ; this is not surprising. considering that the ratio is 16.18 to 1.
The -same hill was employed to demonstrate that
either foot or 35 hand brake would 50 with ease hold the gross load of ao 4 tons 17 cwt. on f
a 1-in-6 slope. 2 15 This brings us to the other brake tests. The company has adopted Lockheed type hydraulic service brakes on all four wheels, the layout being neat and simple.
The brakes are found to act progressively and with good balance as between individual wheels, and the results, indicated on an accompanying graph, compare well with the mean figures for petrol-engined 2-tonners. It will be observed that curves are not included showing the action of the hand brake alone; this is because the brake acts through the transmission drum and is intended mainly for parking, although it may be used in emergency, in conjunction with the foot brake.
The slightly greater weight of the Mercedes Benz, by comparison
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(Right) Acceleration is steady AS up to the governed engine 4-0 speed of 2,000 r.p.m., which 55 gives 41 m.p.h., the curve 50 rising evenly from 10 m.p.h. 25
with petrol vehicles of this class, seems to give it an advantage as regards suspension. The springs are of ample size and absorb road shocks well. It may be mentioned that in the place of spring shackles a slipper arrangement is adopted for the rear ends of the four semielliptic springs. There is no tendency to pitch when traversing a bad road, and the lateral stability is good.
The steering gear is of a rather high ratio, 24 turns of the steering wheel sufficing between left and right locks; at speed this is restful for the driver, and we did not detect any undue heaviness of action when manceuvring.
The easy gear change has already
been mentioned, and it may be noted that the ball-change gear lever and the thumb-release hand-brake lever are located on the driver's left. To the right of the brake pedal is a pivoted accelerator plate. The instrument board accommodates an oil-pressure gauge and a speedometer, there being no other dials.
Below the heater-plug switch, within the cab, is the two-volt heater-plug battery, and there is a red light on the dash which indicates automatically • when the dynamo is not charging (provided the switch-key is in). Bosch electric direction indicators are fitted, their control being mounted on the dashboard. Near this are two convenient levers, one controlling the quantity of fuel injected (and, of course, being connected to the accelerator pedal), whilst the other controls in jection timing. A Bosch electric wiper is fitted to the single-panel screen. A feature of the Germanbuilt cab is that it has a padded fabric roof, which is light and free from drumming.
For those who require tipping gear, provision is made for a power take-off from the third-speed layshaft wheel, whilst arrangements also are made to fit a mechanical tyre pump at the front of the radiator, where it is driven from the starting-handle dogs.
As regards the silence of the vehicle, whilst it cannot be denied that when ticking over the engine Is not so sweet as a petrol engine, the impression is lost when a normal speed is reached on the road. In this connection a feature is the fitting of n large vibration damper at the front end of the crankshaft. It is noticed that the dynamo, starter, oil tiller, dipstick and air cleaner, together with inlet and exhaust manifolds, are on the near side of the engine, where also there is a full-length detachable inspection cover over the water jacket of the cylinder block.
The block and crankcase form a single iron casting with the usual Mercedes-Benz wet cylinder linings, these being fitted so that they can be drawn out by hand. The enginegearbox unit is supported on four Silentbloc bushes. The dynamo and fan share a common V belt, the water impeller being mounted on the fan shaft. Free access to the power unit is obtained by removing the bonnet sides and top.