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SIX-CYLINDER BUSES IN GERMANY.

14th February 1928
Page 60
Page 60, 14th February 1928 — SIX-CYLINDER BUSES IN GERMANY.
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The N.A.G. Concern Adopts a New Power Unit of Interesting Design for Certain of its Products.

(NNE of the largest builders of motor V./lorries and buses in Germany, the Nationale Automobil Gesellschaft, of Oberschonweide, Berlin, which has supplied a large part of the fleet of vehicles used by the General Berlin Omnibus Co., has hitherto mainly concentrated its efforts on chassis equipped with engines of the four-cylindered type. In keeping with the trend of events this concern has recently brought out a new six-cylindered engine, rated at 80-100 h.p., which it is now employing both in 5-ton lorries and in motorbuses.

The new engine, of which an illustration is given on this page, is interesting in that, whilst its six cylinders are cast en bloc, the detachable heads are formed in pairs, only the combustion chambers of two cylinders being exposed at a time when each head is lifted. The bore and stroke are 108 mm. and 160 ram. respectively, the maker stating that 80 h.p. is developed at the normal speed of 1,200 r.p.m. and 100 h.p. when the engine is accelerated to 1,700 r.p.m., the compression ratio being 5.2 to 1. The valves are of the overhead type, operated by overhead rockers and enclosed pushrods off the camshaft which is carried in the crankcase. A notable feature of the design is that different diameters are used for the inlet and exhaust valve heads.

The pistons are made of a specially light metal known as Alufit, whilst the crankshaft runs on four wide bearings supported in the upper half of the crankcase. The oil and water circulations are pump-maintained and the water inlets and outlets are below the detachable heads, so that no water may enter the cylinders through the head joints.

c38 The radiator fan is of Elektron metal, the three blades and their boss being cast in one piece. Ignition is by magneto and both a lighting dynamo and starting motor are provided.

The inlet and exhaust piping are located on the off side of the engine, the exhaust pipe being carried forward, until it takes its downward sweep below the chassis, this arrangement being followed in order to prevent overheating of the driver's cab.

A special feature of the new engine is the method Of supplying the mixture to the combustion chambers. Two carburetters, one large and one small, are used, these being so arranged that at any engine speed between the minimum and the normal, that is, up to about three-quarters of maximum power, the gas is supplied by the large carburetter. When more power is needed and the engine is accelerated, the small carburetter is also brought into action, and it furnishes a supplementary gas supply.

At first glance it would appear that such an arrangement would give rise to a "flat" spot in the running of the engine as the second carburetter comes into and falls out of use. The company claims that, as a result of many experiments, which have included the special designing of the induction pipe to ensure an equal volume of gas supply to each of the six cylinders, the twin-carburetter plan has been found to give excellent results in practice—far better, it is asserted, than is possible when two carburetters are used, one for each set of three cylinders. This is largely owing to the difficulty experienced in getting two carburetters, even of identical design and dimensions, to function in precisely the same manner.

The company is fitting the new engine to several of its Mrs chassis. The vehicle shown in the accompanying illustration is a 30-seater, low-loading, single-deck bus, in which the new power unit is embodied. To economize space the driver's cab is mounted at the side of the engine. Incidentally, the power unit overhangs the front axle to a

considerable extent.

The transmission iu the vehicle which is illustrated includes a cone-type clutch, a four-speed gearbox, and 'bevel gear to the back axle. Internal-expanding, servo-operated brakes are provided on all road wheels, whilst there is an • emergency brake of the externalcontracting type at the rear of the gearbox.

The detachable steel-disc wheels are shod with low-pressure pneumatics of 40-in. by 8-in. dimensions, twins being used at the rear. The bus has a wheelbase of 15 ft. 9 ins. and an overall length of 28 ft. 7 ins. Incidentally, the front track is 5 ft. 8 ins, and the rear 5 ft 11 ins.


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