America Prefers Unorthodox Engine Positions
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AMOST interesting lecture on the t re n d of development in America, illustrated by lantern slides, was given at Edinburgh on February 9, before the Scottish Centre of the Institute of Road Transport Engineers, by Mr. S. Holland and Mr. G. D. Robinson, M.I.Mech.E., home sales manager and chief designer, respectively, of the Associated Equipment Co., Ltd.
In their observations the authors pointed out that, with the exception of New York and Chicago, the single-deck bus solely is employed throughout both countries, and where used the doubledecker is rapidly disappearing. Several reasons are given for this, but the real one is undoubtedly that whilst in theory the permitted overload is 100 per cent., that at peak hours is often over 200, the limit being the number of passengers that can crowd in. Single-deckers seating from 40 to 44 regularly carry over 100. In some cases, the seats are being removed to make room for more to stand.
Good Engine Accessibility
Engines are mainly either at the rear or underneath, the majority of operators preferring the former, giving the reasons as ease of removal and accessi bility. The units range between 160 and 212 h.p. Hydraulic torque con
verters are genet-411y employed on vehicles for city services, and the trend for long-distance coaches is in the same
direction. Chassisless construction is found on every modern bus.
Because of extreme temperatures, all buses have doors operated by compressed air, and modem types employ forced ventilation. In Canada, double windows are fitted in the winter.
One-man-operation with pay-as-youenter is general, the standard fare being from 5 to 10 cents: The layout and design of the vehicle are centred On the driver.
He has to see fares dropped into the machine, give change if necessary, issue and receive transfers, remove coins from machines after they have been automatically counted, sort them into a special change container, and open and dose the doors, mere driving being almost incidental: all this in rush hours with 100 or more people crowded into the bus.
The long-distance coach is virtually the king of the road, and even on arterial highways passes everything, this being assisted by a strident horn.
The authors had one experience of a journey of about 12 miles in a limitedstop bus carrying something over 100 people in the rush hour. The speed was in the region of 75 m.p.h., whenever this could be attained. When the vehicle arrived at the terminus the brake drums were smoking, whilst the paint had burnt off the wheels long before. The driver said that there had been some 814 brake fade, but the vehicle had continued within five minutes. The authors assumed, therefore, that such conditions were normal.
Air brakes are almost general and appear to be most successful and trouble-free.
The condition of buses was, in many cases, not as good and rarely better than that of vehicles in Britain, which is surprising, for America did not suffer, as we did, during the war from such severe shortages of labour and materials.
in the maintenance shops, layout and equipment seemed unusually poor, and little could be learnt. A notable exception, however, is the repair shops of the St. Louis Public Service Co. The authors had never previously seen such well-laid-out and beautifully kept shops, but there was nothing to approach them at any other undertaking visited. The lighting is fluorescent. There are wellspaced metal benches, and the men supply most of their tools, excluding specialized equipment. Those working at a low level are seated on low trollies with castor wheels and two lights; each man also has his own little trolley for tools, bolts, etc.
Maintenance Arrangements Usually, hydraulic hoists raise buses for maintenance, but at St. Louis the rear-engined vehicles required only pits, which have three clusters of fluorescent tubes along each side. Also at the end of each pit are two swivelling lamp standards with fluorescent tubes. The ratio of cleaners to mechanics is one to every 40 men.
Any lifting of units after removal is carried out on swing arms mounted on stanchions at various points. These swing the units on to benches, etc.
Cleaning of parts is carried out in a large room with tiled .walls, exhaust fans removing steam and hot air. Degreasers were found to be too expensive, therefore cleaning is carried out by power guns using hot water and a form of soda ash, the parts being placed on grids.
Two fine examples of monocoque construction are the Twin coach with all-aluminium body, and the Mack, which has sheet-steel stampings and pressings for the main frame and aluminium panels. The Mack seems superior in design. It is built by placing two light steel " chassis" members in a jig at the end of the conveyer. Crossmembers, outriggers and spring brackets are welded on.
Then come the metal floor, main airconditioning duct and wheel-arches,
with some of the piping and subassemblies, every operation being jigged, Side pillars extending to the centre of the roof are welded together in large jigs hinged at floor level. Framing up and welding the body sides takes only 43 minutes. Body ends are standard, the length being varied only by the sides, and the tolerance is only i in.
Whilst the rear engine is the most popular, results are unsatisfactory from the cleanliness aspect. Air outlets arc through louvres, and the lower part of the back of the body becomes covered with black dirt; the engine, too, is often a mass of filth. The cooling fans are excessively noisy.
At the Greyhound Company's shops, a large section deals with the welding of broken crankcases. The engine location gives the driver no warning that a mechanical failure has commenced, often resulting in a wholesale smash up.
Some makers are standardizing on the under-floor engine, claiming better weight distribution and, strangely enough, improved accessibility. Running adjustments can often be made from inside the vehicle. The authors believe that arguments against this type are mostly inspired by prejudice.
G. M. Two-Stroke Oil Engine
The virtues of the oil engine are being appreciated, but the only one in numbers in buses is the General Motors' 200 h.p. two-stroke, which, compared with our standards, is inefficient. Smoke has caused trouble, and has been overcome only by using special fuels approaching pure kerosene.
The White Motor Co. is fitting a 12cylindered under-floor petrol engine, the most complicated unit the authors have ever seen installed in a bus, but it appears to be giving a reliable performance, as is the Hall-Scott under-floor type of 130 and 180 h.p. and the 230 h.p. vertical, the last being for trucks and fire-engines.
Worm-driven rear axles have almost disappeared, probably not being sufficiently robust for the great horse-power employed. Most axles are bevel-driven and are noisy. Hypoicl gears are not much used, but the Timken Company has standardized such a type for truck axles. Orthodox spiral bevels are said to cover mileages of from 200,000 to 500.000, but the maintenance shops
showed many failures. In one wellknown American vehicle the rear-axle noise is predominant.
Woven brake facings have been replaced by the compressed-block type, which retains its friction at higher temperatures, although the coefficient is believed to be less than that of the woven. On big buses the brake facings are bolted on to the shoes.
Much use is made of the S-type brake cam, which allows longer wear without -using packing. The parking brake is always of the transmission type.