WARNING: Where a "Power Timing Light" is used, DO NOT connect the "Battery Lead" connec­ tion to the alternator output terminal, as this could cause alternator diode failure.

Spark Plugs

Spark plugs must fire properly to assure proper engine performance and emission control. In most cases spark plugs will operate satisfactorily for the scheduled period, after which they should be replaced.

If misfiring occurs before scheduled replacement, re­ move the spark plugs for inspection. Appearance or con­ dition can reflect a wide variety of engine conditions:

• Normal Conditions

Normal conditions (Fig. 6). This plug has been running at the correct temperature in a "healthy" engine. The few deposits present will probably be light tan or grey in colour with most regular grades of commercial fuel. Electrode burning will be in evidence; gap growth will average not more .than about 0,03 mm (0.001") per 1600 km. Chances are the plug, as pictured, could be .~leaned, the gap electrodes filed, regapped and reinstalled with good results.

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Fig. 6-Normal conditions

• Co.ld Fouling

Cold fouling or carbon deposits (Fig. 7). This dry black appearance is fuel carbon and can be due to over rfch fuel-air mixture, possibly resulting from a faulty choke, clogged air cleaner, improper carburettor idle adjustment, or dirty carburettor. However, if only one or two plugs in a set are fouled like this it is a good idea to check for

Fig. 7 -Cold fouling

1-2-5

sticking valves or Iauuy ignition cables. This condition also results from prolonged operation at idle.

• Wet Fouling

Wet fouling (Fig. 8) tells you that the plug has drowned in excess oil. In an old engine, suspect worn rings or excessive cylinder wear.

Remember that "break-in" fouling of new engines may occur before normal oil control is achieved. In new or recently overhauled jobs, such fouling plugs can be cleaned and reinstalled.

Fig. 8- Wet fouling

• Overheating

Overheating (Fig. 9) is indicated by a white or light grey insulator which appears "blistered." Electrode gap wear rate will be considerably in excess of 0,03 mm (0.001") per 1600 km. This suggests that a cooler heat range should be used ... however, over-advanced igni­ tion timing, detonation and cooling system stoppages can also overheat the correct spark plug heat ranges.

Fig. 9-0verheating

• Plug Removal

To remove the plug leads, grasp the nipple at the end of the wire and rotate slightly to break the adhesion be­ tween it and the spark plug insulator, then use a straight steady pull to remove.

CAUTION: Removing secondary leads by grasping any areas other than the nipple can cause lead stretch and subsequent excessive secondary circuit resistance.

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