Better Performance: Equal Consumption
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Seddon 6-7-ton Chassis with Perkins 108 b.h.p. Engine has Adequate Power for Mountain Work or for High-speed Trunk Haulage
By Laurence J. Cotton,
LTHOUGH the Seddon
7-tonner with the Perkins R.6
engine will find a ready market Drseas, its style will )be cramped in s country where the 20 m.p.h. ed limit prevails for vehicles ighing over 3 tons unladen. In iition to fitting the larger engine an alternative to the Perkins P.6 it in the 7-tonner, there have been ?rovements to the braking system, :hat the brake-facing area has been reased, and a Clayton Dewandre
7-in, servo incorporated. This kes for increased safety under all ving conditions.
[he new engine, larger-section es, heavy-duty rear axle, I-in.;k frame and improvements in king are complementary in raising unladen weight, with 16-ft. platm body, to 3 tons 8i cwt. flowr, when tested over a course near .nchester, there was no great .erence in the fuel-consumption
rate in comparison with a standard P.6 model carrying 18 cwt. less payload and equipped with a two-speed axle.
Apart from putting the air filter outside the bonnet but in the cab, there is no other outward indication of the R.6 unit being installed. It fits snugly into the space normally occupied by the smaller Perkins engine and the gear lever is extended to the normal position in relation to the driving seat. This latest Perkins unit is a shortstroke engine with the Aeroflow system of combustion, set to give 108 b.h.p. at 2,700 r.p.m. In respect of its high governed speed, it approaches contemporary petrolengine design for commercial vehicles, but scores in its higher and fiatter.torque curve, 240 lb.-ft. being derived at 1,500 r.p.m. Because of the short stroke, the piston speed is kept low, which is conducive to reduced bore and ring wear.
• The unit is mounted low in the chassis, so preserving the good forward visibility which is a feature • of Seddon vehicles, and a Borg and Beck 13-in.-diameter clutch with solid centre plate and segment facings is provided. A Moss five-speed gearbox, together with a heavy-duty spiral-bevel-drive axle, are other items in the specification. Formerly, Seddon vehicles were equipped with hypoid gears, but spiral-bevel units are now used throughout the range.
Another change in the 6-7-tonner is in the reduction of brake-drum diameter at the rear by using wider shoes at both axles, so increasing the brake-facing area by 62 sq. in., equal to 161 per cent., and at the same time improving drum cooling. The use of a larger servo on chassis with the R.6 engine is justified.
The frame, springs, front axle and cab are common to both 6-7-ton chassis but the Manes 611 steering box is provided in the new model to deal with faster travel over indifferent roads. The test vehicle was equipped with 8.25-20-in, covers of 12-ply rating, which, according to the S.M.M.T. reconimendations, a.10 afford a total running weight of 10 tons 4 cwt. where the domestic schedules apply. There is an alternative in the 9.00-in.-section tyre which increases the advocated gross operat• ing weight to 10 tons 7 cwt. overseas, or permits total weights of up to 12 tons in this country.
For my tests six one-ton blocks • were loaded on the platform, which, together with heavy road springs and lengths of securing timber, gave a total payload of 7 tons 6 cwt. and a gross laden weight, with crew, of 10 tons 18 cwt. The chassis was straight from the assembly line, and apart from about 20 miles initial road work for adjustment and ferrying to the Seddon bodyworks and weighbridge, had done no further work before the start of my test.
To make the test comparable wiff that of the Seddon fitted with th smaller engine and two-speed axle, followed the same course as befor, and within 10 minutes of leaving th works was tackling the Lower IDcN hill climb across the Pennines. Ligl rain made the cobbled ma( treacherous, but the Seddon kept straight path during braking at suffered no side slipping on corner With several sharp rises in a dire mile climb, I was able to stage star ing tests on various gradients. / the steepest section of 1 in 5, the was no difficulty in moving off wi bottom gear engaged and on E. incline of 1 in 9 starts were accor plished in second gear.
There was no doubt that the larg engine afforded better performani than on the test of the smalle engined model with two-speed ax] in a straight hill climb, and ti measured distance was covered in le time. The water temperature was little higher than.before, the readin ranging from 154° F. at the botto to 181° F. at the top, with a d reading of 54° F. Possibly the engi, was not fully warmed to its task the beginning of this test, and wi less initial friction in the engine the would be a lower temperature diffi ence in normal running.
This was my first test of a ft forward-control vehicle with the F engine fitted, and the new pov unit would appear to be sligh quieter on full throttle than the I engine. The air induction roar v noticeable, but on overrunning 1 larger unit was found to be by the quieter. A trunk driver woi
robably put some sacks or radiator tuffs over the bonnet to reduce the oise.
Consumption trials were made on ie Manchester road, and the first tempt of the 10.4-mile circuit was tarred by eight stops, whilst I had to )1low a slow-moving convoy up a -adient, using third and fourth gear ir over 3 min. This produced a lel-consumption return of 12.01 t.p.g., which is well below the rerage expected for a trunk haulage :.hicle of this type.
A repeat run, when only three voluntary stops were made, proiced a better result, and although [direct gears were again required for min. when returning from the Mantester end of the circuit, the fuelmsumption rate worked out to 5.56 m.p.g. There was no significant fference between this return id the 15.5 m.p.g. afforded by the st' with the alternative power unit. the speed restriction on vehicles eighing over 3 tons unladen is moved, many operators will make Le change to the latest Seddon ause of its economy, coupled with Ater performance.
In its acceleration, the test vehicle as quick off the mark, and using
only the second, third and fourth ratios, from 0 to 30 m.p.h. occupied 36.3 sec. Obviously, the vehicle is geared for high speed if 30 m.p.h. can be reached in an indirect gear. In addition to the new condition of the chassis there was no suitable level ground for testing maximum speed, but judged by its performance estimate this as 50 m.p.h.
There was so much reserve braking power that the wheels could be locked on a good road surface without heavy pedal pressure. Taking an average of 12 tests at 20 m.p.h. and 30 m.p.h., stopping distances of 28 ft. and 58 ft. respectively were recorded, Tapley readings ranging from 68 to 80 per cent. From these results and tentative fade tests when descending the Pennine gradients, it was apparent that the Seddon could offer consistent braking, and would not require adjustment very often. It would probably operate a 30 m.p.h. schedule with less attention than some of the vehicles built specifically to come within that class.