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THE LEYLAND OIL

13th January 1933
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Page 46, 13th January 1933 — THE LEYLAND OIL
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■ IGINE TRIED OUT

ALTHOUGH the general principles of the Leyland oil engine have been known and illustrations and references to the unit have been made in this paper during the past year or so, the company has avoided, until the present time, any offictul announcement of its introduction, preferring to allow service tests to continue for a lengthy period in order first to establish the all-round satisfactoriness of the power unit. We have recently been invited to Leyland to subject the oil-engined maximum-load four-wheeler, called the Bull, to our standard form of road test.

The general design and type of combustion chamber used in the oil engine are claimed to be British and exclusively Leyland. The layout of the engine is similar to that of the company's well-tried overheadcamshaft petrol engine, certain details having, of course, been modified and certain working parts strengthened to take the heavier loads of the compression-ignition cycle. The fact that important components, such as the clutch, sump and timing-gear details, are common to both engines has an important bearing upon maintenance costs for users employing both types.

Despite the more robust construction, ample bearing areas, etc., the oil engine weighs just over 1 cwt. more than the petrol engine. This, and the fact that the power units are interchangeable in the chassis, further facilitate conversions. The engine and gearbox form a unit with three-point mounting in the frame.

Technical data are given in the accompanying panel, and it may be noted that, whilst the governed speed is 1,800 r.p.m., the engine can, the maker claims, be satisfactorily run at much higher speeds; the output and speed are definitely limited to ensure a sustained output with reasonable fuel consumption and maintenance costs.

By reason of the overhead camshaft, the cylinder block contains no tappets or push rods, the consequent simplicity yielding a sound casting with accessible holding-down bolts. A single iron casting forms the cylinder head and, as this carries all the valve gear, valve grinding and adjustment can be effected on the bench, whilst in less than an hour a spare head can be fitted.

The combustion chamber is of the direct-injection B32 type, and is formed as a simple cup in the top of the piston. The natural movement of the air entering the cylinder is used to bring oxygen in contact with the fuel particles, the flow being orderly and non-reversing, and the chamber is designed to be free from heat losses of the more complicated kinds.

The piston cavity is slightly to one side, and the fuel is injected obliquely towards the piston centr e, being kept well away from the cylinder walls, where it might detrimentally affect piston -ring lubrication as well as possibly causing crankcase dilution.

To ensure a sufficiently rapid air swirl the inlet

valves are screened on one side, thus directing the air stream. For this reason these valves are keyed in their guides and, to remove them, the keys and their circlips must first he removed. It is important that the valves should be correctly timed, as with a carelessly assembled camshaft, the valves might be struck by the pistons. The camshaft is so arranged that the exhaust valves may be lifted slightly prior to starting by hand, or when adjustments are being made to valves, etc.

Fuel injection ranges in period from about 5 degrees of crankshaft rotation at no load to 25 degrees at full load. The valve of the single-hole nozzle is set to lift at about 1,500 lb. per sq. in., the pressure varying from this to about 2,500 lb. at high speed. The compression of the air reaches about 450 lb. per Sq in., its temperature rising to about 1,000 degrees F. An important feature is that no injection-advance device is fitted.

As regards constructional features, the mainbearing caps are spigoted in place and held by bolts, which pass through the cast-aluminium crankcase to the base of the cast-iron cylinder block, and it may be noted that, at an extra charge, an Elektron crankcase can be provided, reducing the engine weight by about 85 lb. The Bosch fuel pump and unit-mounted governor are fitted, these and the exhauster—in fact, all auxiliaries except the C.A.V.-Bosch 24-volt starter— being accessibly mounted on the near side.

The connecting rods are of H-section heat-treated nickel steel, the pistons are of heat-treated Y-alloy with gudgeon pins. The fuel filtration is thorough and orthodox, and it is recommended that the fuel be flat turned off at night, so that, should there be any slight leak, air may not be drawn in. The entire valve gear is lubricated under pressure and an accessible oil filter and cooler is mounted in front of the sump.

With respect to chassis-maintenance features, which we always regard as coming within the scope of our road-test reports, it may he noted that the engine can be withdrawn forward without removing the gearbox, the gearbox itself is easily lowered, the clutch adjustment is accessible, and the final-drive unit is withdrawn after removing the torque tube forward sufficiently to permit the axle ease to be turned over in the spring chairs. Chassis lubrication is grouped.

'No opportunity presented itself for observing the engine start from cold, but instantaneous starting was obtained regularly with the warm unit. The chassis and engine tested had covered only 60 miles following engine bench tests. Reference to the accompanying vehicle diagram will show that the chassis was slightly overloaded from the legal standpoint, there being no practical means for correcting this. It may be noted that, with an 8.19-to-1 axle ratio, the Bull chassis is largely employed for trailer work, but that we tested it as a solo machine with a 7.15 axle.

Throughout the day the amount of exhaust smoke 3333

emitted never exceeded a steamy, grey haze, except when the laden chassis was wrongly driven up a steep hill with full fuel supply at a very slow engine speed. The puffs emitted after deceleration were only of slight intensity and in normal running the exhaust was not visible. The idling of the engine is distinctly regular, and there is quick response to fuel control when the unit is accelerated without load, also a correspondingly pleasing pull-away when accelerated under full load ; the acceleration is rather better than with the Ley-land petrol engine, and can be studied in detail in an accompanying graph.

The housing of the engine in the forwardcontrol model is sensibly constructed and remained cool all day, not forgetting, however. that the weather was cold and no cab was fitted. The fact that there is no control of the engine timing simplifies matters for those employing drivers of comparatively little intelligence, although this class is rapidly dithinishing.

The laden chassis performed well on hills, and the 1-in-7i gradient known as Sheep Hill on the Leyland-Blackburn road was ascended at a steady 10 m.p.h. in second gear. A restart in first gear was easily effected on the 1-in-7i slope, whilst on a 1-in-9 gradient a comfortable restart was made in second gear.

Details of our fuel-consumption test are given in the accompanying panel, and the result of 12.73 m.p.g. is satisfactory. During this 35-mile run, the speedometer was checked for speed and distance, whilst at the end of the journey the radiator temperature was found to be 156 degrees F.; a thermostat in the cooling-water circuit, incidentally, controls vertical radiator shutters.

The remainder of our report deals with a chassis already

well known and—it may be said— well suited for oil-engine propulsion, whether used with or without a trailer. The braking system incorporates a vacuum reservoir and exhauster, there being two Dewandre vacuum cylinders operating on opposite ends of a cross-shaft. A useful fitting is a pressure gauge embodied in the instrument board, the maximum negative pressure recorded being about 22 ins.

We carefully checked the number of vacuum-brake applications that could be made after stopping the engine, and concluded that two

good applications (the gauge reading respectively 22 ins. and 17 ins.), and two weaker applications (13 ins. and 8 ins.) could be made. The test was conducted on a steep hill, and we satisfied ourselves that, after the vacuum was exhausted, the driver could, with physical effort on the pedal, easily hold the 12 tons on a 1-in-9 gradient. We may draw attention to the good feature embodied in the hand brake, this being of the multi-push ratchet type, which gives excellent leverage and power.

The chassis is easy and pleasant to control, the Marles steering being comfortable in all conditions, light, practically irreversible as regards bumpy road surface, and slightly self-centring. The clutch acts beautifully and the gear change is positive and easy. The springing is good and does not glee rise to unpleasant pitching, neither is there any instability in cornering.

Our opinion is that this is a well-built machine, adequate for the demands of the present-day haulier, soundly constructed and safe upon the highway. The oil engine is satisfactory in road service, even when judged by the exacting standards of the Leyland petrol-driven units. Its introduction et the present juncture is an important step on the part of Leyland Motors, Ltd., for no range of goods chassis that includes models for maximum legal loads can to-day be considered complete if oil engines be not available as optional equipment. The fact that the new unit is interchangeable with the Leyland petrol engine and incorporates several components that are identical is valuable.

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