The Daimler 8•6 Litre DI Oil Engine
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FOR many years, engines of proprietary make have been incorporated in Daimler passenger vehicle chassis. Although these units have given satisfaction in use, it was a natural step for the Daimler concern, with all its resources, to produce its own oil engine. Plans were laid 11 years ago, and experi mental engines were running for two years before the war. This work was interrupted by the factory's change-over to the manufacture of war equipment. A further setback occurred as a result of damage to the premises, but eventually work was resumed and the engine was put into production in 1945.
Like all other engine prototypes, it had its teething troubles, but, with its faults rectified by modifications, the engine is now presented as a reliable and economical proposition.
The crankcase and cylinder block are of monobloc construction with renewable dry liners fitted to the cylinder bores. The crankcase is of generous width at the base and careful ribbing ensures inherent rigidity. The six vertical cylinders, with a bore of 4.5 ins, and stroke of 5.5 ins., give the total displacement of 8.6 litres. There are two vertical overhead valves per cylinder, arranged in line and operated by overhead rockers, short push-rods and hollow cast-iron tappets bearing on a camshaft mounted high in the block.
Drive to Fuel Pump
The driven auxiliaries are on the near side, and are coupled to the gear groups at the flywheel end of the crankshaft. The helical gears, five of which are steel and the remaining three of east-iron, are all mounted on ball bearings. It is claimed that the impressively steady and quiet idling speed of the engine is a result of taking the drive to the fuel pump through the gear drive from the flywheel end of the crankshaft. This reduces the cyclic speed variation to a minimum, causing little or no disturbance on the light governor springs.
Fuel is injected, by either C.A.V. or Simms equipment, directly into a pot-type combustion chamber offset in the piston crown; the compression ratio is 15 to 1. The injectors are of the four-hole type, the spray angle being 140 to 150 degrees. The engine is governed between 350 r.p.m. and 1,700 r.p.m.
The fuel pump is driven through the Clayton Dewandre vane-type exhauster (for vacuum brakes). A suction pipe from the exhauster draws oil from the base to facilitate lubrication, being drained back into the sump through a second pipe.
The water pump, mounted on the front of the engine, is driven through a jack-shaft by a gear mounted below the exhauster drive. Gear drive to the camshaft, mounted on the offside of the engine, is through the same train of gears which links up the exhauster drive on the opposite side.
The crankshaft, a nitrided steel stamping, is carried by seven steel-backed bearings lined with copper-lead alloy; they are of 335 ins. diameter. The cast-iron main-hearing caps are secured by six studs on the centre and rear mains. and four studs on the front and intermediate bearings Thrust on the crankshaft is taken by the front bearings.
The pistons are retained on the connecting rods by fully floating gudgeon pins of 1.5 ins. diameter. Six hardened and tempered rings are fitted to each piston.
A gear-type lubrication pump is mounted inside the crankcase, and driven by a helical gear engaging with the timing wheel at the rear of the crankshaft.
The connecting rods of nickel-steel stamping are drilled for pressure lubrication to the gudgeon-pin bushes, Detach. able steel-back copper-lead-alloy-lined bearings of 2.81 ins, diameter are fitted to the big-ends; these are secured by two bolts per connecting rod