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MUD—PLUGGING By,ohnF Moon

23rd July 1954, Page 42
23rd July 1954
Page 42
Page 44
Page 45
Page 42, 23rd July 1954 — MUD—PLUGGING By,ohnF Moon
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THERE are very few oil-engined, medium-range four-wheel-drive vehicles in use at the present, mainly because most operators of such specialized transport prefer a high-revving petrol engine for " bullat-a-gate " tactics when crossing rough ground and climbing steep gradients. But the Perkins R.6 engine, as installed in a standard Bedford R-type 3-ton 4 x 4 lorry, showed itself to be quite capable of extracting the vehicle from seemingly impossible conditions and to have more than sufficient power to scale inclines which would normally need full engine speed with a comparable petrol-engined job.

The usual reason for using an oil engine is that of fuel economy, but that was not the sole aim in this case. When operating on an isolated site, all engine fuel has to be delivered in cans and is not easy to safeguard. Petrol is an attractive commodity with many other uses than propelling commercial vehicles, whereas oil fuel does not offer such possibilities and is therefore not so likely to be used unofficially. Furthermore, the

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oil is easier to store in the open in bulk and is less prone to evaporation and fire risk than petrol.

The conversion already referred to has been carried out independently by the transport department of British Insulated ' Callender's Construction Co., Ltd., and is not officially authorized by Vauxhall Motors, Ltd., although that company offered all possible advice while the work was in progress. A normal Perkins conversion kit, as supplied for the Bedford S-type range, was used, and with the exception of a few minor detail modifications to chassis and engine, the standard procedure was followed.

Because of the depth of the R.6 sump and the height of the frontaxle final-drive housing, it was obvious that under full bump conditions the sump would be fouled. This snag was overcome by cutting back a section of the base directly above the axle pot and welding up at an angle of 45°. In order not to take any chances, one-inch packing pieces were also welded to the underside of the bump-rubber stops, this having the effect of reducing the axle movement. The effectiveness of this arrangement was proved during the

severe suspension test over the Tanktesting ground at Long Valley.

A further modification, not necessary with the S-type conversion, was made to provide access to the front sump bolts. These were obscured by the engine support member when the

engine was originally installed and so would make sump removal almost

impossible. The bracket was modified, quite simply, to give sufficient

clearance for a socket spanner without affecting the mounting arrangements.

• Straightforward Conversion Standard alterations associated with the Perkins conversion include the provision of a 24-v. electrical system, with additional batteries and carrier, alterations to the exhaust pipes and additional plumbing in the fuel tank, but the job is, on the whole, quite straightforward and does not

require eiiner specialized knowleoge or equipment.

The R.6 engine fits neatly into the chassis frame without disturbing the transmission, and no alterations are necessary to the engine cowling or radiator mounting. The four-speed synchromesh gearbox is common to all Sand R-type models but has no provision for a power take-off; this is arranged on the transfer box, which is flexibly mounted. It drives to the two axles by single-piece propeller shafts. Four-wheel-drive is automatically engaged when low ratio A Clayton Dewandre vacuum servo is mounted on the outside of the right-hand frame longitudinal, power being supplied by an enginedriven exhauster through a large reservoir. The Lockheed tandem master-cylinder is attached to the servo, and this acts through hydraulic wheel cylinders on both axles.

Having joined the Bedford in North London, we drove to Farnborough by way of the Great West Road with the object of making a fuel-consumption run en route. A faulty stop-watch foiled my efforts on this run, but while in the cab I noticed that an unusual degree of heat was coming from the engine. Unusual, because the Perkins engine normally runs rather cool, whereas the top-tank temperature was 169° F.

On arriving at the proving ground it was decided to attempt the test slopes first. A loose-sip-faced grade of 1 in 2.74 was tackled, using low gear and four-wheel-drive, and this was surmounted with only partthrottle. The climb seemed so effortless that I suggested a second-gear

assault, but this proved too much for the engine, which can hardly be wondered at. A really quick change into low took the 4 x 4 over the top without any rolling back or use of brakes.

The next slope was of 1 in 2.43 severity, and the surface was bad, heavy rains having washed sections of it away making the under-surface crumbly. The first attempt in low gear failed just short of the top. Spin developed at all wheels and they ploughed deep furrows in the loosepebbled surface. Reversing down was performed in perfect safety and a second run then made. This also failed, but I feel sure that had the tyre pressures been reduced from 60to 30-1b. per sq. in. the top would have been reached.

During this climb, steam appeared from the radiator overflow and the cause of the heating during the run from London was discovered. The whole of the radiator had been blanked off in order to raise the engine temperature for the fuel run and this, of course, caused the boiling under the arduous climbing conditions.

When the radiator had been refilled, a low-gear, half-throttle at 0

climb was made up the 1 in 2.25 concrete slope. On the way down a successful hand-brake test was performed, and after turning round a stop-start trial on this grade was made. There was slight spin at the near-side front wheel for a moment, but the vehicle then pulled away without further skidding. While on this slope, a slight seepage of oil from the rear main-bearing was noticed, but according to the oilwarning light lubrication pressure was being maintained satisfactorily.

The most impressive part of the day's test came when the Bedford was taken on to the Tank ground for cross-country trials. The surface here was deeply grooved and consisted for the most part of a sticky mixture of soft sand and loam interspersed with loose-bedded pools and steep hillocks.

During most of the half-hour ..,pent under these conditions, the 4 x 4 ploughed its way steadily and relentlessly over the course ' after the fashion of the Tanks with which it shared the ground. The second gear was used as much as low gear, and it was not until the front differential-housing became wedged in a ridge between two deep ruts that traction was lost. However, by shunting back and forth the vehicle got out on to firmer ground and outside assistance was not necessary.

Shield for Banjo

Although the front-axle banjo cover is of thick toughened material, I consider that some form of shield would be advantageous. This could be arranged to lift the axle bodily when striking a solid obstruction, thus enabling the vehicle to be backed away without getting immobilized.

The modifications to the front suspension were successful in preventing damage to the sump, although the operators are considering making a further change by replacing the normal bump-rubber by one of thicker section. This would preclude any likelihood ef the rubber bending off the stop.

Throughout this run I was standing in the body and supported by the cab, and was therefore able to get some idea of the articulation between cab and body allowed by the three-point rubber cab-mountings and the flexibility of the chassis frame. Although the terrain was extremely rough, the suspension was not tried beyond its limits and the damping on both axles prevented dangeeous bouncing . from taking place. This run, as for the gradient tests, was made with tyres at full pressure.

On completing the cross-country section, I took the vehicle through to Farnborough for consumption trials, but after two runs of five miles each it was obvious that something was at fault with the fuel-injection equipment. An average figure of 13.2 m.p.g. was returned, the engine was not pulling well and there was abundant smoking from the exhaust.

This figure was much lower than was expected, even allowing for the additional transmission losses, the general tightness of an almost new vehicle and the cross-country tyres, so it was decided to check the pump and injectors and complete the test at a later date.

When I next took the .Bedford over, one week later, the pump-timing had been reset—it was 2° retarded—and two dribbling injectors had been replaced by new ones. The engine felt decidedly more lively and so I took it out to the Rochester Way for fuel tests.

Return runs between Bexley and Southfleet, along a busy and undulating main road, produced an average

figure of 14.95 m.p.g. for an average speed of 27.6 m.p.h., this including one traffic-light stop and a long climb requiring third gear for three minutes. For this test the radiator bottom-tank was blanked off, but the water temperature did not rise above 130° F., the ambient temperature being 60° F.

Braking and acceleration trials were conducted along the same road. The relatively light rear-axle loading caused the rear wheels to lock under emergency-braking conditions, but the figures obtained were not dis appointing. From 20 28.75 ft. Were required to bring the vehicle to a halt, the figure from 30 m.p.h. being 59 ft., equivalent to 0.51 g.

The specification of a servo system is fully justified, as extremely heavy pedal-pressure would be required to obtain these figures were it not fitted. A Tapley reading of 31 per cent, was given when the hand brake was applied at 20 m.p.h., the pull-up action of the lever enabling full advantage to be taken of the leverage.

Acceleration figures were only a little slower than for an equivalent petrol-engined truck, 12.6 sec. and 23.6 sec. being necessary for 20 m.p.h. and 30 m.p.h. respectively from a standing start. The Perkins engine pulled well from 10 m.p.h. when in direct drive, and 20 m.p.h. was reached after 15.0 sec., with 30 m.p.h. taking 16.8 sec. longer. Maximum road speed obtained was 47 m.p.h., but this would haVe been higher had conditions allowed.

The vehicle behaved admirably throughout both days' testing and was pleasant to drive. The steering was light in spite of the large-section tyres, and .cab ventilation, when required, was satisfactory. I did not like the long gear-lever travel between low and second gears and because of this awkward stretch I made the standing-start acceleration trials with second gear engaged.

The reverse-stop spring is rather weak also, and there was a tendency to engage reverse instead of second. These are only minor criticisms and in all other respects I was entirely satisfied with the vehicle and consider the conversion to be well worth while, resulting as it dOes in a 50 per cent. saving in fuel without loss of performance.

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Locations: London

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