"MISFIT" PLUGS.

Auckland Star, Volume LXIX, Issue 126, 31 May 1938, Page 16

"MISFIT" PLUGS.

GIVE UNEVEN FIRING.

OVERHEATING DANGER.

Why is it so important, when fitting replacement sparking plugs, to buy the exact type and grade recommended by the plug makers for the particular engine? asks an English writer. To the inexpert eye one standard type plug looks very like another, and consequently the motorist is apt to regard the official recommendation more as an advertisement than a piece of sound advice. He does not, perhaps, actually understand just what is wrong with the wrong type of plug for his engine.

There are several reasons why the makers' advice should be strictly followed, one of the most obvious being that different kinds of plugs have different "reaches." The general rule, as laid down by experts, is that a plug should have its points flush with the wall of the combustion chamber or cylinder head. If the #each is too short, the points will be recessed in the wall or head, and consequently the plug will fire in a pocket of dead gas, caSising difficult starting and uneven firing at low speeds.

On the other hand, too long a. reach means that the points will protrude into the combustion chamber and rwill quickly become overheated, with the danger of pre-ignition, loss of power, and possible damage to the engine.

It is impossible to be certain from the mere look of a plug whether it has the right . characteristics for your engine. The makers' recommendation chart, therefore, is the best and simplest guide when plugs have to be replaced.