A NEW Scottish-built
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DOUBLEDECKER
Further Details of an Interesting Halley Chassis Built to Carry a Large-capacity Passenger Body
.1 N our issue dated November 11th, 1930, we 'dealt with a new six-cylindered power unit evolved by Halley Motors, Ltd., Ioker, Glasgow, for service in double-deckers ; we are now able to give some further particulars of the chassis in which it will serve.
The machine is known as the type P821. The following are its leading dimensions :—Wheelbase, 16 ft. ; overall length, 25 ft. n ins.; dash to end of frame, 20 ft. 4 ins. ; frame height, laden, 1 ft. 9.1, ins. ; rear platform height, 111 inn; chassis weight, 3 tons 11 cwt.; standard tyres, 36-in.. by 8-in. front, 34-in. by 7-in, dual Tear; optional equipment, 40-in. by 101-in. front, 36-in. hr 8-in, dual rear.
An inspection of one of the first complete chassis revealed to us the 'unusually strong frame Ivhich has been
employed. The side members Sweep downwards in gentle curves at the dash line to a maximum depth of U. ins., the flange width being 3 ins. Each side member is pressed in one piece throughout. A striking point is the lateral bracing. At the front is a downswept
channel-section cross-member ; next comes a cast-steel bridge which serves as one of the anchorages for the enginecarrying sub-frame. Between the gearbox and the rear wheels there are three 4-in, tubular cross-members and a 3-in. one just behind the rear springs.
• Four semi-elliptic springs are mounted directly beneath the frame members. All four springs have a marked reverse camber at full load and employ SilentbIoc bushes. The front springs are located at their rear ends. The rear springs, which are 5 ft. by 31 ins., take both driving and torque stresses. At the front of the forward crossmember are two brackets which carry the radiator. These incorporate rubber pads to insulate the block. Through the cross-member in question passes the forward end of the engine-carrying subframe, which can oscillate in a rubber bush. A similar insulation is employed for the two rearward mountings of this sub-frame.
The unit-mounted gearbox, with single-shaft control from a gate on the near side of the driver, offers indirect ratios of 1.55, 2.54, and 4.35 to 1, whilst reverse is 5.63 to 1. The standard ratio of the Kirkstall underslung-worm axle is 6.25 to 1. The shafts are fully floating and the casing cover is in Elektron.
Special attention has been paid to excluding oil from the brakes. Adjacent to the brake pedal there is a handoperated adjuster; thence the effort is taken to a Dewandre vacuum servo, a master adjuster, a distribution shaft, and then to the four-wheel brakes. The hand brake consists of separate shoes in the rear-wheel drums, which have shrunk-on, anti-squeaking bands.
Provision has been made on the engine for the installation of a Westinghouse compressor when this braking system is specified.
An interesting form of clutch is employed. It is of the two-plate type, which enables a reasonably small diameter to be used, thus avoiding excessive encroachment on floor space in the gangway. A central pressure spring is employed, and adjustment is effected by means of three screws.
In connection with the transmission system it is interesting to note that the intermediate bearing of the propeller shaft allows the primary shaft to be swung aside so that the complete gearbox can be dropped, without further disturbance of the propeller shaft or engine.
Turning now to the sidevalve engine, to which we referred last year, its cylinders have a bore of 4k ins, and a stroke of 5 ins. The crankshaft runs in seven main bearings, a special bearing at the forward end taking the clutch thrust.
This engine will develop up to 115 b.h.p., but the normal setting gives about 95 b.h.p. at 2,000 r.p.m. At the front end of the crankshaft is a sprocket for a duplex chain which -drives the camshaft and fan, also the magneto through skew gears. From another sprocket on the camshaft a triplex chain drives the water pump, dynamo, and? if required, the air compressor. The water pump has a spring-loaded, conical, graphite gland of the type which requires no attention.
Special care has been taken to ensure adequate lubrication of the auxiliary drives as well as of the larger bearings. The dual gear-type pump in the crankcase is directly driven from the crankshaft ; one portion of it feeds the main bearings, big-ends and camshaft, whilst the secondary part feeds the distribution chains and skew gears, care being taken to see that centrifugal force aids effective penetration of the oil. In addition to a plate-type strainer in the sump, there is a sleeve-type filter horizontally placed below the magneto ph6tform. On the aluminium crankcase casing is mounted the monablec cylinder casting which incorporates six " wet " barrels mounted in the familiar Halley manner. There are two separate cylinder heads embodying Ricardotype combustion chambers.
From the Solex carburetter the mixture passes to a bifurcated hot-spot in the primary pipe, which' then feeds separate hot spotted 'induction tracts, each of. which supplies three cylinders.
Other interesting engine details include the use of steel connecting rods with white metal run directly into the bigends. The • floating gudgeon pins . are located: by spring circlips in:the .nluminium pistons, each of which has three compression and two scraper rings.
. The magneto is located transversely, and has automatic control, but thereis .additional hand .control, giving a_turther 10 degrees advance. For the hand settings of the Magneto and carburetter Ahrens .flexible controls are employed.
The starting, handle has a lug for the -Eqvihipple &Vice, but a 12-volt C.A.V. 'electric motor is supplied if required.