MISUSING A CAR

Rotorua Morning Post, Volume 2, Issue 544, 30 May 1933, Page 2

MISUSING A CAR

USE OF THROTTLE TOP GEAR SLOGGING WILL WEAR 'THE ENGINE. FULL OPEN UNWISE. (With acknowledgments to the N.R.M.A.)

Only in rare cases is it possible to overload the working parts of a motor car engine far beyond the normal limits, but there are other ways in which an engine may be misused, resulting in wear and even bearing failure, although' the engine has not been overloaded dn the accepted sense of the word. ' ' The big-end bearings connecting the rods to the crank-pins are undoubtedly the danger points in a modern high-speed engine. These have to transmit the whole power of the engine in addition to rotating at a high speed. Safeguarding them is a very thin film of oil, which is continually being sheared as the crank revolves, and which has to transmit terrific pressures with'out being squeezed out from between the surface. Great Heat. A great amount of heat naturally is generated. ' The temperature of the big-ends is apt to rise to within a narrow margin of danger joint 'if an engine is kept hard at it for any length of time. The slightest shortage of oil is sufficient to enable the heat to melt the white metal of the bearing. If a car is being driven for long distances at high speed, it follows that while 55 m.p.h. may be maintained with safety hour after hour, 60 m.p.h. may spell disaster if the engine is not in tip-top condition. Those speeds are chosen merely as an example, of course. It is a good rule not to cruise at highei* than 90 per cent of the maximum speed of which the oa.r is capable. That one has a considerable margin of power at hand is one of the charms of a fast car. Two Loads. Two kinds of loads are borne by the pistohs, connecting rods and bearings — the pressure of the expanding ga.ses, and the inertia of'the reciprocating parts. The second occurs only at high speeds. The piston objects to being brought to a standstill and started again after each stroke, and it gives an upward pull when at the top and a downward pressure a.t the bottom, always trying to continue its motion unchecked, but h'eld in leash by the connecting rod. This inertia effect may become even more important at very high speeds than the load due to the explosion. Such revolution speeds can be reached in ordinary touring cars only on an intermediate gea.r or by driving down a hill in top gear at a speed well above the maximum attainable on the level. Lazy Drivers. Again, if the engine is kept slogging hard uphill at a low revolution speed without retarding the ignition the working parts may be overloaded. If the spark is timed accordingly, slow pulling does no particular harm. The lazy driver does not bother about using the hand-operated system, so that, when his poor power unit is pulling hard uphill at low revs., each piston, rising on the compression stroke, suddenly " reeeives the full force of the explosion before it reaches the full force of the explosion before it reaches the top. Naturally there is considerable sh'ock, expressed dn audible knocking or rough running. At a low speed the oil pressure is usually low, too, and ther|e i|S consideiM)^ r'Ssk of damaging the bearings. The lessons t0 be learned, therefore, are to avoid prolonged full-throttle high-speed running, and to change to a lower gear or retard the ignition when top gear speed is low.