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A New Dorman 41itre Oil Engine
Page 88
Page 89
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The Ajax, a Fourcylindered Unit Developing 60 b.h.p. at 2,200 r.p.m. and Weighing 884 lb. with Starter and
Auxiliaries
T is evident from a study of recent / designs of oil engine for road transport purposes that great progress has been made during the past year or so in obtaining a power-toweight ratio more closely in line with that of the petrol engine, and, at the same time, in maintaining a degree of silence which would, a few years ago, have been considered impossible. This remark was prompted by a cursory examination of the new Dorman Ricardo power unit, for the engine is extremely compact and of neat and workmanlike appearance, develops 60 b.h.p. at 2,200 r.p.m. and weighs only 690 lb. Considering the fact that it is priced at a competitive level, such a powerto-weight ratio must be considered as being outstandingly good.
It has a bore and stroke of 3i ins. (95.25 mm.) and St ins. (142.87 mm.) repectiveiy, which ' give a swept volume of 4.075 litres, the unit developing 30 b.h.p. at 1,000 r.p.m., 47 b.h.p. at 1,600 r.p.m. and 60 b.h.p. at 2,200 r.p.m. Maximum torque
1380 occurs at about 1,100 r.p.m. and amounts to 159 lb.-ft.; the minimum fuel-consumption figure also occurs at about 1,100 r.p.m., at which speed a trifle more than 0.4 pint per b.h.p.hour is consumed.
It will be seen from accompanying illustrations that the cylinder block and crankcase are formed in one casting, which extends well below the centre line of the crankshaft. This construction not only helps to attain low production costs, but provides a highly rigid foundation, for the five
main bearings of the crankshaft,. Made in chromium iron, the Casting is a good example Of the founder's art, for the walls of the case, the cylinder bores and the water-jacket enclosures are of remarkably uniform thickness, despite the thinness of the section. The crankcase is completed at its base by an aluminium sump (capable of holding 23 gallons of oil) with a well formed at the rear end in such a manner that when inclined at an angle of 15 degrees (equivalent to a gradient of 1 in 4) the pump suction pipe is always submerged providedthe oil level is kept within the limits on the dip-stick.
Housed in this well is a large cylindrical filter, into which the pump suction pipe fits; the pump itself is driven from the forward end of the crankshaft by helical gearing. Delivery to the main bearings is effected by a large-diameter gallery pipe attached to the bearing caps, the big-end journals receiving their supply of oil through the usual drilled passages in the crankshaft.
From a by-pass an oil-line is led to the overhead camshaft and rocker gear, with a passage offset from the line to incorporate an A.C. Sphinx filter operating on the " bleed " system. All the camshaft and rocker bearings are positively fed with lubricant, whilst the overflow from the relief valve is arranged to lubricate the timing chain.
A one-piece casting forms the cylinder head, which is secured to the main casting by no fewer than 20 studs of 1-7-‘-in. diameter. The head carries vertically disposed valves in replaceable guides and 'supports three bearings for thecamshaft, the valves being operated by bell-crank rockers. The distri
bution gear incorporates a --in.-pitch triple-roller chain, which embraces sprockets on the crankshaft, the fuelpump and water-pump driving shaft, the fan spindle, the overhead camshaft and, on the off side, a Reynolds automatic tensioner.
The whole of the overhead mechanism is enclosed by an aluminium cover of rather unique design. In addition to maintaining an oil-tight enclosure, the casting forms the means for connecting the air cleaner to the air inlet ports in the head. This is effected in a simple manner; two cored passages of circular section run horizontally from the outside of the case, and then turn do6v-nwards to register with vertically disposed " Siameezed " ports in the cylinder head. This arrangement simplifies the exhaust-passage layout, and allows the exhaust manifold to be of perfectly straightforward design.
Ricardo swirl chambers are employed in conjunction with C.A.V.Bosch pintle-type injectors and electric heater plugs,
Other components of interest are the pistons. which are formed in R.R.53 aluminium alloy and are equipped with three pressure rings, one slotted scraper. ringabove the . gudgeon pin and. .a. simitat 'SciaPer ring below the gndgeort pin. Of H-section, the connecting rods are of nickel-chrome.
. Cooling has received special attention. The system incorporates a centrifugal pump, running at half engine
speed. A thermostat fitted to the outlet pipe is set to commence opening at 75 degrees C. and to be fully open at 90 degrees C.