THE MOTOR WORLD

New Zealand Times, Volume XLIII, Issue 9955, 26 April 1918, Page 8

THE MOTOR WORLD

ENGINE KNOCKS

SOME HINTS TO AID IN DETECTION.

Knocking in an engine is one of the hardest things for even the experienced repair man to identify, because most of the internal noises, while they indicate that something is not right, are so nearly alike in character that it is most difficult to distinguish tho causa of one from another.

It is only possible to diagnose motor knocks in a sort of general way, for even though to the txepenenccd ear a certain knocking may appear to be caused by too advanced a spark, for instance, it may in reality be caused by a loose rod bearing or a shaft bearing. But the more experience a man gets with the particular motor ho is driving, the easier it is for him to.. tell j ust what any kind of a knock in that engine results from. Some of the knocks, of course, are easier to distinguish than others. For instance, it is usually possible to tell a loose piston knock from the others. This is commonly called a piston slap. GENERAL CAUSES OF KNOCKS.

Generally speaking, there are about five causes of motor knocking. Those are:. Spark badly carbonised, loose connecting rod bearing, piston too loose, cylinder worn, or a ring broken; loose main bearing. ‘ Tho first of these—namely, spark knock—is, perha£j„ about the most commou knock, apu uie one with which tlie average driver is most familiar, it may usually be -distinguished by a rather dull, metallic sound, which is in contrast to the sharp sound of metal striking metalSupposing a coin or a key is wrapped in a tnickness of newspaper, and then gently tapped against the enamelled metal part of a desk telephone. This will be a close imitation ot an ignition knock, but the best way to know the sound of this noise is to make tho car pull a heavy load w-ith. a spark fully advanced.

The spark knock is due to the spark being so far advanced in relation to the speed of tie engine that the ofiarge is ignited before compression is' completed, the. tiring of tho charge exerting a sudden downward force upon tho piston before it should receive that downward impulse. The remedy is very simple. P'ull the spark lever down lower on the quadrant until the knocking stops, or remove tho load from the motor by throwing out tne clutch, or slow' down the motor. Tne _ general indication of a carbon knock ia a fairly clear and hollow, pounding which is specially evident when the engine is hot and when on a hard pull, such os through deep sand or ut> a good grade. Carbon knocking is due to excessive carbon deposits on cylinder walls, piston heads, etc. The carbon particles become red hot, due to the intense heat within the combustion chamber, and they ignite the charge before compression is completed and the piston is in position for ignition to take place. In other words, it is a pre-ignition knock. Improperly adjusted carburettors which send too rich mixtures to the cylinders, poor lubricating oil, and excessive use of oil are the three main factors in the following of carbon incrustations. THE ELECTRIC VEHICLE. The increased shortage in petroleum fuel, which threatens to become acute the world over, offers a great opportunity for the wider introduction of electrically-driven vehicles, which depend for their supplies on power developed by other classes of fuel, or water-power ■whonel available. The decUfic vehicle is by no means an experiment, for it has performed most satisfactorily for a number of years for both pleasure and commercial purposes, and has proved itself eminently practicable. This tho public does not appear to be generally aware of, as the more spectacular or sonsatisual,

features of the petrol-driven ear have monopolised attention. But impending conditions will undoubtedly force a wider recognition ,of the undoubted merits of the electric vehicle.