CARE OF SPARK PLUGS

Bay of Plenty Times, Volume LXXVI, Issue 14639, 7 April 1948, Page 4

CARE OF SPARK PLUGS

POINTS TO LOOK FOR Making Sure Of Proper Temperatures Frequent Causes Of TroubleSatisfactory spark plug operation requires that the insulator nose and electrodes shall bo maintained at a temperature sufficiently high to burn carbon accumulations, but not high enough to causa detonation, preignition, fusing or blistering of the ceramic surfaces, or rapid erosion of the electrodes.

Spark plugs are made in several heat ranges, hot, medium and cold. Hot plugs have a long insulator nose, cold plugs'a! short nose, and medium plugs a medium length nose. Proper temperatures deponed upon use of hot plugs in a cold engine, cold plugs in a hot engine and medium plugs in an engine {hat operates under ordinary conditions.

The colour of the insulator nose will indicate whether the right spark plugs have been installed in any given engine. Before making a comparison in this manner, it is essential that engine performance prior to the inspection has been normal. Any irregular operation, particularly prolonged idling in vehicles not ordinarily subject to this service, will affect the appearance of the plug and prevent making an accurate diagnosis.

Then too, identical types of spark plugs frequently show wide variations in appearance even though used in the same make and model of engine. Any such deviation from characteristic appearance is usually the result of conditions external to the spark plug. A detailed examination of such plugs frequently suggests the remedy for the faulty condition. Powdery Deposit Spark plugs operating under normal conditions wall have a soft powdery deposit on the nose of the insulator, eithef grayish tan or rusty brown in appearance depending upon how long the plug has been installed without cleaning. Electrode erosion will be normal and is confined to the immediate faces of the spark gap. However, the electrodes should be carefully checked, because certain types of ignition coils and magnetos have spark discharge characteristics that • produce rapid plug electrode erosion without otherwise affecting the appearance of the plugs.

Spark plugs operating under conditions that are too hot can be classified in three groups. First, a plug operating for a short period under excessively hot conditions, will show the insulator nose white in colour with dark spots or blisters near the tip. There is usually no excessive electrode erosion.

The second group includes • plugs that have been operating for a long period of time under conditions that are too hot. The insulator nose will show fused and blistered , dark coloured deposits near the tip with excessive electrode erosion. The third group includes those plugs which have- been operating for a prolonged period of time under extremely severe conditions or ode-rating in an engine with water leaking into the combustion chamber. The deposit on the insulator nose, or oven the ceramic material itself, is badly blistered and fused. Both the centre and the side electrodes will show excessive erosion. Five Main Causes Most frequent causes of the above trouble, with the exception of the last which indicates water leakage, are (1) spark plugs not sufficiently tightened*in the cylinder head, (2) improperly seating valves, (3) excessively lean air-fuel mixture, (4) ignition timing improperly adjusted, (5) using plugs too hot for the particular installation.

Spark plugs operating in an engine that is too cold will usually show a “sooty” sludge that will cover the insulator tip or completely'fill the gap between the shell and the insulator. This is usually caused by a condition that permits oil to reach the combustion chamber. An excessively rich air-fuel mixture may aggravate it. Caution should be used in making examination as such a condition can be brought about by prolonged idling prior to inspection, preventing the spark plugs from reaching normal operating temperatures. The utmost care should be used when cleaning a spark plug. Never should any instrument be used to

gouge out accumulations of carbon between the insulator nose and the electrode. Rather, the spark should be placed in a cleaSine machine after the right adapter ring has been chossn. Caro should be exercised while the plug is cleaned by the abrasive spray b " cause if it is left in too long’ thn abrasive may wear the insulator .nose- sufficiently to change ‘ the thermal rating. Once the plu<* w been cleaned, it should be placed over the blower in order that thcarbon dust -and abrasive can be removed through air pressure. Rules For Gap Setting If new spark plugs arc necessary gap setting and installation should be carefully done in order that the best possible performance can ho obtained. The following rules should b* structly adhered to: (1) Be sure the gan is s «t in accordance with the * car manufacturer's specifications. -a-u----(2) When checking gaps, do not a l«A r . ? auge - but tools for this pperation. If it inecessary to re-set the gap, bend the side electrode only, taking ca?e not to strain the centre elected! °' (3) Use only well-fitting socket wrenches as loose socket wrenchor open end wrenches may result in damage to the plug. y result (4) Tighten plugs "sufficiently to insure heat transfer from the to thei engine cooling system. Always install with a new gasket. vay °