ligher speed, more power,
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lower fuel consumption
By P. A. C. Brockington, A PA I Mech E
&PART from certain details of construction, there can be no question marks regarding the new Gardner 6LXB diesel. The mg-awaited news of this unit will be greeted by operators everythere without doubts that it will run as reliably as the older engine nd, Gardner says, more economically, despite an increase in its ited r.p.m. It is, in fact, remarkable that an improvement in output f 30 b.h.p, has been achieved by raising the rated speed by 50 r.p.m. by detailed modifications, and that at the same time the linimum specific fuel consumption has been appreciably reduced. The 6LXB develops 180 b.h.p. at 1,850 r.p.m. (compared with 50 b.h.p. produced by the 6LX at 1,700 r.p.m.) and has a governed o-load speed of 1,980 r.p.m. Its maximum torque of 536 lb/ft. ; developed at 1,000-1,100 r.p.m., which compares with a torque of 85 lb/ft. at 1,100 r.p.m. of the 6XL and it is notable that—as an be seen by reference to the characteristically flat torque curve— le torque is maintained within 95 per cent of this value over a peed-range ratio of 3 to 1. The performance curves represent net alum subject to deductions arising from operation of the fan, enerator, compressor and so on.
An approximate dry weight of 1,580 lb gives a weight-to-power atio of 8.8 lb/b.h.p., and as the two units are dimensionally similar, part from minor changes to the manifolds, me power-to-bulk ratio ; also improved. In common with 6LX the unit has six cylinders vith a bore of 4.75 in. (120.65 mm.) and a stroke of 6 in. (152.4 mm.), he swept volume being 638 cu.in. (10.45 litres).
Protagonists of the long-stroke engine inevitably quote the lardner as an outstanding example of obtaining the maximum fuel
consumption benefit from the combustion advantages offered by this type of unit. The consumption and efficiency figures of the 6LXB should further enhance the reputation of the maker for producing the most economical automotive diesel engines in general service. The minimum specific fuel consumption of the engine is 0.328 lb b.h.p./hr., which represents an overall thermal efficiency of 40 per cent. Consumption at maximum output is not increased to more than 0.336 lb b.h.p./hr. Moreover, if the engine is operated at mid-speed at some 10 per cent below maximum torque, thermal efficiency is raised to the remarkably favourable figure of 40.5 per cent. The minimum specific fuel consumption of the 6LX exceeds 0.33 lb b.h.p./hr.
Modifications obscure The nature of "the modifications to many components" mentioned by Gardner is in many cases obscure, notably with regard to the improved breathing ability of the unit and the ways in which its increased speed, mean effective pressure and heat throughput have been accommodated. But it is significant that special reference is made to the flow efficiency of the inlet manifold and to the increase in bore of the induction connections, conduit and air cleaners to 5 in. The shape of the pistons has been modified to give improved heat flow and stress distribution and there have been changes to the shape of the combustion chamber, the diametralclearance contour, the cylinder-head clearance and the gudgeon pin. Other components that have been modified include fuel injectors,
injection pump, advance-and-retard linkage, governor, water pump and flywheel, whilst the speed of the radiator fan and air compressor has been changed. Additional cylinder-head holding-down studs have increased their number to a total of 48.
Gardner states that it would be impossible to convert older 6LX engines to the 6LXB specification and that it would be impracticable to convert the latest 6LX engines because of the shortage of many of the components and their cost. It is also pointed out that the increased power would have to be accommodated by employing a matching clutch, transmission, cooling and "induction systems, auxiliary drives and so on.
In general, the design of the 6LXB follows well-proven Gardner practice and includes the use of a cast-iron, dry-linered detachable block of one-piece construction and of two cylinder heads, each of which covers three bores. The aluminium crankcase extends some 5 in. below the crankshaft centre line and is preloaded vertically by 14 cylinder holding-down studs that extend to main-bearing steel bridges and by 12 transverse bolts that span the unit.
As with the 6LX this form of construction provides a saving in weight of around 300 lb together with quiet operation, whilst the high relative expansion of the aluminium and good heat conductivity enable the cold bearing clearances to be reduced to a minimum and afford rapid heat dissipation.
Fully-machined crankshaft
The crankshaft is machined all over from a die-stamping of chromium molybdenum steel and has hollow bored crankpins and main journals, which reduce stress concentrations and loading of the main bearings. The shaft runs in eight bearings, which comprise a roller bearing at its forward end and seven prefinished copper-lead overlay-plated shells. Scientifically flaw detected, the shaft is dynamically balanced in its final stage of production.
Polished as well as machined all over, the connecting rods are also produced from die stampings of chrome molybdenum steel and are rifle-drilled from end to end to provide lubrication for the special copper-alloy small-end bearings. The big-end bearings are similar to those of the crankshaft journals and the connecting rods can be withdrawn through the cylinder bores.
The pistons are cast in the Gardner foundry from medium silicon aluminium alloy and are of Gardner patented design. It is emphasized that their unusual length affords a very large area of contact with the cylinder walls, which promotes good heat transfer, facilitates quiet operation and reduces loading and wear. The two pressure rings are chromium-plated on their side faces as well as their peripheries, whilst the single oil-scraper ring is of hardened and tempered cast iron and is of drilled U-section. Aluminium pads are fitted in the ends of the fully floating gudgeon pins to give endwise location, the diameter of the pins being 1.8125 in.
Formed in the piston crowns, the combustion chambers are hemispherical and receive fuel spray from centrally located injectors, which are of Gardner design and manufacture. The injectors are held in place by a single stud and a clamp lever and a conical seat in the cylinder head provides a gas-tight metal-to-metal joint. It is claimed that a vehicle mileage of 100,000 miles before injector servicing is required is by no means unusual.
Vertically located, both the inlet and exhaust valves are fitted with dual springs and faced with Stellite, the valve-seat inserts being of the same material, whilst the valve levers and fulcrum shafts are case-hardened all over. Hand turning of the engine for adjustment (and for starting if the flywheel is suitable) is facilitated by a decompressing device. Coolant is transferred from the block to the cylinder head through synthetic-rubber joint rings which are separate from the joints of the solid-steel gaskets. A CAV BPF fuel-injection pump is incorporated in a Gard camshaft governor assembly and the complete unit is trunni mounted in permanent alignment on the engine crankcase. ' camshaft has a diameter of 1.5 in. and is supported in three it ball journal bearings. It is emphasized by Gardner that the standing rigidity of the shaft is favourable to injection chai teristics as well as wearing properties.
Noise in the driving gears is reduced to a minimum by so profil the cams that torsional reactions arising from the combined for of the fuel-plunger springs and the tappet-return springs are, as as possible, neutralized. Lubricant in continuous circulatior supplied to the cam tappet governor unit from the main oil pui A Gardner standard type of injection advance-and-ret mechanism is employed and, also in fine with standard pract means are provided for individual hand operation of each injec plunger to facilitate priming and testing. Mountings are embed in the unit for fitting a diaphragm-type fuel-lift pump and a gt type, oil-cooler circulation pump. Dust-proofing is afforded total enclosure of all working parts.
Mounted in a low position on the engine and gear-driven from camshaft, the coolant pump delivers water to the base of cylinders for circulation to the cylinder heads, temperature coni being provided by a Gardner dual wax-type thermostat and (in case of a standard system) by a fan of 24-in, diameter driven triple belts, which absorbs 2.7 h.p. Accommodation is availa for a range of electrical equipment, air compressers, power-steer pumps, engine mountings and so on. A wide range of air clean and other auxiliary equipment is available.
Many of the ferrous as well as non-ferrous castings are produi in Gardner foundries and a large number of components manufactured with the aid of Gardner-designed machine to built in the works.