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A LARGE OIL-ENGINED BUS TRIED OUT
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MANY hundreds of buses with Crossley compression-ignition engines are now in daily use in various towns and cities throughout the British Isles. Practically all of the power units of these vehicles are of the direct-injection type; a new engine, however, has recently been evolved utilizing swirl chambers in the combustion heads— a design which has been influenced by Mr. H. R. Ricardo.
A fully illustrated description of thiS unit (available as four and sixeylindered models known as the VR4 and VR6 types) has already appeared in our pages, so that in dealing with the road performance of the 48-seater bus, which forms the subject of this review, it will be necessary to make only a brief reference to the details of construction of the engine. '
As will be seen from the tabulated 002
performance figures, the pistonswept volume is slightly greater than 9 litres, the bore and stroke dimensions being 4:11iins. and 6 ins. respectively—i.e., exactly as in the directinjection type of Crossley unit. The engine is governed to run at a maximum speed of 1,700 r.p.m., at which rate 100 b.h.p. is available at the flywheel. At 1,000 r.p.m. 62 b.h.p. is developed, the power curve being almost a straight line.
Torque Characteristics.
The torque characteristics are interesting, the maximum figure of 3,940 lb.-ins. .being obtained at 900 r.p.m.; at 1,400 r.p.m. the torque figure is as high as 3,840 lb.-ins., whilst even at the governed speed of 1,700 r.p.m. torque is maintained at 3,730 lb.-ins. At 1,000 r.p.m. the fuel consumption works out at .45 lb. per b.h.p.-hour, whilst the consump
tion curve runs almost_ flat from 1,200 r.p.m. to 1,700 r.p.m., giving .472 lb. per b.h.p.-hour.
We can now see how the performance of the engine in a vehicle operating under road conditions compareswith its bench-test characteristics.
First comes the question of starting from cold. By using the electric air heater and the heater plugs in the combustion chambers, the electric starter made the engine spring into life from stone cold after about three crankshaft revolutions, the unit firing with perfect regularity thereafter. Merely as a matter of precaution, the engine was allowed to run for several minutes to warm up the oil somewhat, before setting off, but, although still cool, one did not notice any sign of refractoriness when the heavily laden bus was taken in the streets of Manchester, en route for the hilly district around Glossop.
Taking things comfortably we averaged 18 m.p.h. over the first 11 miles, which included a climb of the famous Mottram Moor hill, the gradient from the Hollingworth side being about I: in 10. The hill itself Is a good test In the sense that it is over a mile in length and the steepness gradually increases towards the summit. The Crossley took the acclivity in "third" the indirect gear being engaged after about 200 yds. of climbing at between 15 m.p.h. and 17 m.p.h. After the change down the speed increased very slightly until just near the top, where it slowed to 15 m.p.h. After the long run on full " throttle " at about 1,300 r.p.m., the cooling water in the radiator showed no signs whatever of boiling.
On the decline from the top of Mottram Moor we tried the brakes and found that at a point where the gradient was about 1 in 10 we were able to pull up to rest from 17 m.p.h. in 50 ft. on a wet surface withont any marked sign of skidding, using only the foot brake.
Next we put the Crossley at The Snake—a long climb over the moors running eastward from Glossop. At first the gradient is quite moderate. By reason of the fine torque charac teristics at low speeds the engine was able to maintain a vehicle speed of around 17 m.p.h. on third gear for the first 400 yards, but as the gradient increased in intensity the speed gradually fell to about 9 m.p.h., at which point the second gear of 14.75 to 1 was engaged. Throughout the remaining 21 miles of climbing, the speedometer needle remained between 9 •m.p.h. and 11 m.p.h., the actual timed ascent of this, the worst part of the hill, being made at 10.9 m.p.h.
Under really favourable weather conditions this should be considered a fine achievement, and when it is realized that the climb was made in a snowfall of Intensity such as partially to obscure the driver's vision besides making the road surface treacherous, the performance must be considered the more meritorious.
A small calculation shows that the engine must have been turning over at its governed speed of 1,700 r.p.m. for practically the whole of the run up The Snake, never once was there the slightest suspicion of faltering, neither did a change down to first gear appear to be necessary. In
other 'words, the engine had plenty of power in hand all the time, despite the gradient, which, in places, must have been as steep as 1 in 7. A. pause at the summit of, the pass for photographs enabled us to check the water temperature again, but it was quite cool—as might be expected considering the gale of bitingly cold wind which was blowing through the radiator.
The homeward run back to Glossop was quite uneventful, the braking system and the good weight distribution making a sharp pull up to rest quite an easy matter, even on the steepest part of the decline. As an indication of the security it might be mentioned that we averaged 17 m.p.h. during this part of our run, all due precautions being taken to corner safely and to keep the vehicle well under control all the time.
The controls handle very nicely, a prominent feature being tile fact that they are light to the touch and are definite in action. The clutch, for example, requires quite a moderate pressure fully to disengage the friction surfaces, and even if the pedal be released with a jerk the take-up of the drive is smooth and progressive. At the same time the freemember is relatively light in weight, so that it is quite unnecessary accurately to gauge the speeds of the meshing pinions, when gear changing, in either an upward or a downward direction. These characteristics, of course, make the vehicle ideally suited to the type of service for which it is intended, i.e., on city routes, where frequent gear changes have to be effected and where about five or six stops and restarts per mile are• the rule rather than the exception.
We have already referred to the fact that the brakes operate easily and that the pedal pressure required for an emergency pull up is distinctly moderate. Suffice it to add that on wet 'and consequently slippery roads the machine pulls up all • square. Steering is-light atirdaccurate, there being little interaction betWeen the road ;wheels and the
• steering wheel, thanks to careful • planning of the steering lay-out and mechanism. ; During our trial we sat in various • parts of the bus and even on the uneven setts of some of the worst roads in Manchester we found the seats to be distinctly comfortable. In the first place, the bus rides " solidly," as it were, there being practically no evidence of rolling or swaying when cornering fast ; at the same time the suspension is quite soft enough to absorb all the major road shocks whilst the spring cushions effectively damp out small vibrations.
Mention should be made of the low entrance platform and the easy run of the stairs to the upper deck. Whilst safety is adequately provided for by efficient hand railing, the stairs are wide and are easily surmounted and descended, so that even elderly passengers should find little difficulty in taking their seats in the upper saloon, during the rush hours of service conditions, when no lower-deck seats are vacant.
Altogether then this Crossley oilengined double-decker must be considered as a vehicle which, in addition to being thoroughly roadworthy, is a robust and substantial • job, capable of withstanding pro longed hard usage. It is obviously economical to operate by virtue of the fact that the fuel consumption recorded during our more than ordinarily arduous test was 9.3 m.p.g.