McLaren 's Latest Oil Engine
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New Types of Power Unit Supplied with Four or Six Cylinders—Air Cells and Flame Plates Promote Turbulence
NEXT month's Commercial Motor Show will mark the public introduction of the new high-speed oil engines, produced particularly for vehicles, by the well-known specialist in this form of prime-mover, J. and H. McLaren, Ltd., Leeds.
The new range, designated LN, comprises four-cylindered and six-cylindered engines. The farmer develops 42 li.h.p. at 1,250 r.p.m. and 50 blip. at 1,400 r.p.m. The larger example has outputs of 63 h.h.p. and 75 b.h.p. at corresponding rates of crankshaft rotation. As both models follow the same general design, we shall deal here with the sixcylindered engine.
A robust aliuninium crankcase carries the crankshaft in seven bearings, the camshaft having a Eke number of supports. Girder-type, ribbed caps are used for the mains, therefore the crankshaft should be securely mounted. A gearwheel at the front end drives directly the oil pump. The last-named supplies the main and big-end journals under pressure,. whilst pipes running up the connecting reds feed the floating gudgeon pins and their floating bushes, also by positive means. The overhead-valve gear receives its supply of lubricant from the main pump.
Steel connecting rods, with two-bolt big-end caps, carry aluminium-alloy pistons. Spring rings provide endwise
location for the gudgeons, whilst three of the piston rings are of the compression type and two are scrapers. With exception of a cut-away portion in the head of each piston—to clear the injector ports—the piston crowns are fiat and give a compression ratio of 14 to 1. The cylinder bore is 105 rum. and the stroke 150 mm.
Each cylinder block comprises two bores, with hardened, dry liners; location is ensured by studs passing right . through to the upper face of each block, whilst the head is held by separate studs. Inclined upwards and mounted
in the cylinder blocks are the injectors, with Bosch nozzles, whilst the air cells and flame plates are carried in openings in the head castings.
Fuel, after passing through filters and anM.L. pump, reaches the injectors, from which it is sprayed against the perforated flame plates placed in the mouths of the air cells. During compression air is trapped in these cells, and its rapid egress, as each piston falls, creates a turbulence which promotes efficient combustion. Torch-holders enter the air cells from above, so that this method of heating, for starting in extreme conditions, may be employed. With an electric 12-volt starter, the engine can be set in motion on full compression and without heaters.
For starting by hand in normal tern, peratures the camshaft is slid to bring into action &compressor cams; these raise all the inlet valves. When sufficient speed has been attained, the full Compression is restored and the engine starts. By sliding the camshaft the other way yet a further set of cams is employed ; these slightly raise the exhaust valves on the compression stroke and give a state of low compression.
Mushroom-shaped cam followers impart motion to the push-rods, which, in turn, regulate the opening of the vertical valves. The last-named are offset from the centre line of the cylinders.
Auxiliaries include a dynamo, electric starter, water pump, and, of course, the fuel pump and governor. The lastnamed limits the crankshaft speed to 1,400 r.p.m.
We took the opportunity for having a demonstration run on an old Leyland chassis equipped with the McLaren sixcylindered engine. With a 6-to-1 axle ratio the maximum speed attained was 35 m.p.h. and acceleration was a noticeable feature. We are given to understand that this vehicle, laden with over 6 tons, can cover over 14 m.p.g..