New G.M.C. Range with Two-stroke Engine
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GREATER economy in heavy haulage is made possible by the introduction of two new series of tractive units by the G.M.C. truck and coach division of the General Motors Corporation. These tractors are powered with oil engines operating on the two-cycle principle, a type-developed by the corporation and which has been so successful in applications to locomotives, boats, heavy-duty trucks and buses. The engines in the new tractors are smaller, more compact and lighter than a four-cycle engine of equal power and offer the advantages of fuel economy, low maintenance cost and long life.
There are three models in each tractor series. Those in Series 640 are rated for a gross weight for tractor, semi-trailer and load of about 20 tons, and Series 650 models at just over 24 tons maximum gross weight.
Series 640 models are equipped with 9.00 x 20-in. tyres and the Series 650 machines have 10.00 x 20-in. tyres.
A four-cylindered engine is used in all cases, the unit developing a maximum of 133 b.h.p., with a net b.h.p. of 118.5. The compression ratio is 17 to 1. A push-rod-operated injector is mounted in the head of each cylinder.
In addition to the normal watercooling system, the piston head is cooled on the under side by oilsprayed from a jet on top of the piston rod, which is drilled throughout its length to provide forced lubrication to the piston pin. Cooling is also materially B8
assisted by the scavenging system which effectively removes the combustion gases.
In this system a blast of fresh air is forced into the cylinder from a gear. type blower through a ring of small ports formed in the removable, hardened, cast-steel cylinder liner. The holes, drilled tangentially, give the inrushing air a spiral swirling motion that sweeps the liner wall clean. The large volume of fresh air forced into the cylinder cools the cylinder wall and the top of the piston before it passes out into the atmosphere.
Prospective buyers of these vehicles are offered several options in changespeed gearing and rear-axle drive. A five-speed synchromesh overdrive gearbox having second, third and fifth-speed gears in constant-mesh, is standard in all models, but two variations of this
type are available. An auxiliary threespeed box with two different sets of ratios may be obtained for use with any main transmission on models having a wheelbase of 12 ft. 9 ins, or more.
There is also a choice of three types of rear axle: a hypoid single-reduction drive; a hypoid double-reduction gear for heavy slow-speed work, and a planetary. two-speed axle designed for heavy, loads and hilly routes or higher speed in level country.
Wide-track front axles align the front wheels with the outside rear wheels, thus contributing JO stability, ease of steering control and reduction of tyre wear. Radiator Cores are protected against the possibility of leaks, as the result of chassis frame distortion, by a surrounding steel frame' supported on the chassis front cross-member by a spring-and-rubber mounting.
Cabs also are cushioned with rubber at the front and rear supports, to reduce transmission to the cab of stresses set up by twisting of the tractor frame. Standard cabs have ample accommodation in all respects and are protected against the entrance of dust and draughts at doors and floor.
In the de luxe cab, curved rearquarter windows, in addition to the large rear window, give the driver extra visibility when manoeuvring at loading docks. All windows are of safety glass. A built-in ventilating system, which can be regulated, circulates fresh air in the cab and prevents fogging of the windows. An optional heating unit can be combined with the system to maintain any desired temperature in the cab.