SPARK PLUG ILLS

New Zealand Herald, Volume LXXIII, Issue 22468, 11 July 1936, Page 15 (Supplement)

SPARK PLUG ILLS

RECOGNISING SYMPTOMS Unfortunately for everybody concerned, not even the most expert motor mechanic is infallible when lie attempts to diagnose, by signs and symptoms, tho minor ills to which cars will develop at times. No less than other experts ho makes mistakes occasionally, or fails to observe some secondary symptom that rules out tho indications of tho obvious ono to which, maybe, his attention is drawn by the car owner. But there are certain signs and symptoms that are almost sure evidence of tho same shortcomings every time. Thus sparking plugs provide definite information to tho observant owner-driver, and as they are so easy to remove and inspect, the motorist who likes to find out things for himself may learn quite a lot about the condition of his engine by removing the plugs occasionally after the end of an ordinary run. For example, if tho inner end of a sparking plug—the insulation adjacent to the electrodes in particular—is black and sooty, one has a sure sign of too rich a mixture, which in turn implies excessive petrol consumption and loss of

power, to sny nothing of the risk of misfiring under certain conditions. If the insulator is white and parched this indicates that the plug has been running at an excessively high temperature, probably due to too weak a mixture; again, the practical effect is loss of power, primarily during acceleration and slow but hard pulling. A red deposit left after tho use of Ethyl fuels need cause no alarm, however. Wot oil on the insulator end, and more so on tho electrodes, means, obviously, that too much oil is working up past the pistons into the combustion chamber. The engine is probably one that has covered a big mileage, for worn pistons, cylinders and piston rings are usually the cause —assuming that the car owner has not been replenishing the sump appreciably above tho high-level mark on the dip rod. But not all old engines with worn pistons, etc., cause wet oil to remain on the plugs. They inav be coated thickly with carbon—burnt oil—and thus give another sign and symptom of over-oiling. What we ought to see when we inspect a sparking plug is a grey-black "business end," without any soot at all.