A Wonderful
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Bird • 13y John F. Moon, A.M.1.R.T.E.
THE key to the highly satisfactory overall performance of the new Dennis Pelican bus chassis
is undoubtedly the power unit. in respect of fuel economy and power, the latest series of Dennis 5.5-litre oil engines puts the Pelican at the top of its class, whilst the low chassis weight which accompanies the straightforward layout should contribute towards many years of economical operation.
Passenger comfort has been maintained, despite the good performance and low unladen weight. Suspension is mod over all road surfaces likely to be encountered on normal service in this country, and engine noise and vibration are far less than usually expected with an underfloor oilengined chassis.
The new_engine is derived from the original 5.5-litre unit, as used in the new Condor goods chassis (The Commercial Motor, August 24), but
has a mechanical governor. It is mounted in unit with the. Meadows 250 C5 five-speed gearbox at three points. A single Silentbloc component in shear supports the front of the engine, whilst single Metacone blocks on each side of the bell housing form the rear mounting and torque-reaction members. Longitudinal movement of the power unit is restricted by a rubber-mounted locating rod at the front of the cylinder block.
Adequate cooling has been assured by mounting the radiator ahead of the front axle. The radiator block is eowled and the six-bladed fan, which is carried in a bearing suspended from an intermediate cross-member, is driven directly from the crankshaft by .a two-piece shaft with Layrub joints.
No belts are used for any of the auxiliary drives. The dynamo is driven from the timing gears, which are at the rear of the cylinder block, and the exhauster has a direct drive from the camshaft. The water pump is located nearly horizontally at the front of the block and is driven by skew gears from the front of the camshaft.
The C.A.V. AA-type fuel-injection pump, which has a mechanical governor, is located behind the engine alongside the gearbox, where it is readily accessible from below and reasonably shielded from road dirt.
En other respects, the chassis layout is conventionally simple. The main longitudinal members, which are 8 in. deep and have 2fin. flanges, are flat and parallel to each other. Pressed-steel crass-members a r e bolted into place and the driving controls are carried on outriggers, so that the driver's footboard is below the main passenger floor level.
Bus Chassis Only The Pelican is not offered as a coach chassis, because the manufacturers are anxious that the performance should not be reduced by running at more than the gross recommended weight of 8 tons 14 cwt., as is likely to happen if a luxury coach body were fitted. The straight frame forward of the front axle does not interfere with the front entrance, as was shown on the test vehicle, which had a Duple 44-seat all-metal bus body.
This body, which weighs 2 tons 91 cwt., has a three-step entrance forward of the front axle, with power-operated jack-knife doors. The gangway is flat and level, and the wheel-arches are not large enough to interfere with passenger comfort. A glazed partition and a hinged bar separate the driver's seat from the' passenger compartment, but • allow the driver complete control over the platform area.
A test load of 4-cwt. iron weights was carried. These totalled 2-1tons, representing 44 passengers, and in addition to myself the bus was carrying two Dennis representatives and various additional equipment. It was thus tested at 1_1cwt. above the recommended weight.
• A run was made to Woolmer Hilt for the first tests'. This-hill, which iS near Haslemere, has an average gradient. of 1 in 7-;!, and is abOut
550 yd. long. The steepest section, which occurs near the top, is 1 in 41.
The journey to Woolmer was along , t h e Guildford-Portsmouth r o a d, during which t was able to assess passenger comfort. Although the engine note was inclined to be highpitched, the degree of noise which
penetrated into the body was small and normal conversation was possible. The suspension was excel, lent and the road-holding was such that corners could be taken fast on a perfectly even keel.
During this run it was observed that the normal temperature of the coolant in the cylinder heads was in the region of 165' F., the ambient temperature at that time being 60' F., hut, following a refreshment stop of half an hour or so, the water temperature had dropped to I40' F. by the time we reached the bottom of the hill. The climb was made in 2 min. 20 sec., and the lowest gear used was second, with the speed remaining constant at 9 m.p.h.
At the top of the hill, the coolant temperature was recorded as I 69'' F., at which the thermostat was not fully open. During a second climb the coolant temperature rose from 160" F. to 167° F. This climb was made at the same average speed, in the same ratios, and on both occasions second gear was maintained for 1 min. 20 sec.
The performance convinced me that the cooling system would be wel! able to cope with prolonged running in hilly areas in tropical climates, whilst I have no reason to doubt the manufacturer's claim of a gradient ability of 1 in 3.12 in low gear.
Two descents of Woolmer Hill were made, both in neutral with the foot brake applied. For the first descent the speed was kept down to
10 m.p.h. It took' 1-4 minutes to reach the bottom of the hill, and a
" crash' stop from 20 m.p.h. produced a Tapley meter reading of 68 per cent:
Descent Warms Drums
The second descent was made at 20 m.p.h. in just over a mintite, and warming-up of the drums produced cnly a slight reduction in braking ' efficiency. An emergency stop from 20 m.p.h. produced a maximum retardation figure of 60 per cent.
Returning to the I in 4+ section, I was able to make an easy start in low gear on only one-third throttle opening. When stopping on this gradient 1 did not have to use undue force on the hand brake to hold the bus and there was no need to apply the foot brake to provide assistance. The hand-brake lever, which is conveniently placed for the driver's right hand, is cranked to enable maximum upward leverage to be exerted.
Several restarts were made in low gear, and all with an equal measure of success, with only slight hazing around the exhaust pipe. I was so encouraged by the torque characteristics of the engine that I then attempted to get away in second gear, but this produced excessive clutch slip and no forward motion. Only rarely will the low gear • of 8.05 to I be necessary during -normal running, the second ratio providing satisfactory performance on gradients of up to 1 in 6.
Returning to the Guildford area, brake tests were conducted on a level stretch of concrete road near Milford. Emergency retardation was commendably smooth and there was little apparent time-lag in the system. Comparisons of the maximum retardation rate, as shown by the Tapley meter, and the average rate as evidenced by the stopping distance, revealed a difference in the region of .05g-a performance rarely equalled even in these days of highly developed braking systems.
The Peasmarsh, near Guildford, was used for acceleration tests and here, again, the Pelican's performance put it on a par with higher c26 , powered passenger vehicles of this size. The direct-drive tests were made from below 10 m.p.h. without harshness in the transmission. and the short time taken to reach 30 m.p.h. is an indication of the high torque characteristics developed at low engine speed.
The smoothness of the transmission, which was a feature of the direct-drive acceleration runs, was notable throughout the series of tests made during two days. When idling at 370 r.p.m., there was only the slightest trace of vibration noticeable in the body, and this was not of sufficient consequence to cause rattles in the body panels.
I do not wish to disparage current all-metal bodywork, but it frequently acts as a sounding board for any engine roughness, particularly with underfloor power units. This was riot the case in the Dennis-Duple combination.
A three-mile stretch of road north of Guildford was used for the consumption trials, measurements being taken over the out-and-return circuit
in each case. Whilst reasonably level, it called at times for the use of full engine power, and as it was not wide, other traffic was liable to cause inconvenience. In view of these conditions, the results obtained are particularly satisfactory.
During those tests in which stops were made, each stop was of 15 seconds, with the engine idling. Wherever possible, the bus was taken up to 35 m.p.h. during these runs and the water temperature during the stopping tests settled down to a maximum of 170° F., the ambient being 59° F.
When making the six-stops-permile run with a full load, the Dennis driver was braking at 0.15g for each stop, and at the end of the test, having made 35 stops in half an hour, an emergency stop from 20 m.p.h. produced no signs of fade.
With all but 31 cwt. of the imposed load retrioved, the suspension was satisfactory and5 once again, there was no trace of excessive engine noise or body drumming.
Driving was particularly easy. The relatively low driving position provides an excellent view of the road ahead, but it is possible to see over vehicles in front. All the controls are light and the gear-change linkage provides a positive action which assists in fast changes. The steering was light at all speeds and I did not detect any trace of wander.
At the Dennis works I was able to carry out a series of maintenance tasks, for which the Pelican was run over an inspection pit. Many of the jobs which I did could be done only from below the vehicle, but routine attention to the cylinder heads, fuelinjection equipment, and oil, fuel and air filters can satisfactorily. be given from ground level, and the dynamo and gearbox can be reached through floor-traps.
Checking Levels
Taking the " non-pit" jobs first, was able to check the water level in the coolant header tank inside 14 seconds. A trap in the near side of the body gives access to the filler rap and is secured by a rubber fastener. The engine-oil level was checked in 1 minute 10 seconds from outside the vehicle, and this time included 45 seconds for raising and lowering the hinged skirt panel. A second oil-level check from the pit was completed in 10 seconds.
The reservoir for the braking system is situated on the left of the driver's seat at floor level and the fluid level was checked in 4 seconds. Another ground-level job was the stripping and checking of the largo oil-bath-type air cleaner. This took minute 10 seconds when done from outside, compared with 20 seconds when carried out from below, the additional time being caused by the body trap,
Fuel-system Service With this off-side trap already raised, I removed the fuel-filter element in 30 seconds and replaced it in 50 seconds, whilst No. 1 injector was withdrawn in 34 minutes and replaced in 31 minutes. Bleeding tile fuel system occupied a minute, and the whole operation was carried out comfortably from alongside the bus.
Descending into the pit I checked the gearbox oil level in 8 seconds and the rear-axle oil level in 55 seconds. The gear-oil level can also be verified through the floor trap, but the rear-axle check is a pit job. The Lockheed combined reservoir and master cylinder, which forms part of the hydraulic Clutchactuation system, is adjacent to the clutch pedal, but very close to the underside of the driver's footboards.
A dipstick is attached to the filler cap and with it I was able to check the fluid level in 50 seconds, but decided that topping up the level would be much more complicated and would necessitate either removing the driver's footboard or using an oil gun and flexible tube.
Greasing has been reduced to a minimum, as all the suspension pivotal points incorporate Silentbloc bushes which require no routine attention. Use of a grease gun is principally restricted to the three points on the propeller shaft and the normal nipples on the steering.
In respect of general maintenance the Pelican is extremely well laid out, which should assure operators that routine workshop attention will be conscientiously carried out.