Examination
1. Before testing, clean spark plugs with carbon deposits or contaminated ones using a special sand jet and blow them with compressed air. If the carbon deposits are light brown, you do not need to remove them, as they appear on a serviceable engine and do not interfere with the operation of the ignition system.
2. After cleaning, inspect the spark plugs and adjust the gap between the electrodes. If the spark plug insulator has chips, cracks, or the weld on the side electrode is damaged, replace the spark plug.
3. The gap between the spark plug electrodes should be within 0.5–0.6 mm for a conventional ignition system and 0.7–0.8 mm for a contactless system. Check the gap with a round wire feeler gauge. You cannot check the gap with a flat feeler gauge, since this does not take into account the notch on the side electrode that forms when the spark plug is operating. Adjust the gap by bending only the side electrode of the spark plug.
Leak test
1. Screw the spark plug into the corresponding socket on the stand and tighten it with a torque wrench to 3.2–4 kgf·m.
2. Create a pressure of 20 kgf/cm² in the stand chamber.
3. Drip a few drops of oil or kerosene from an oil can onto the candle; if the seal is broken, air bubbles will escape, usually between the insulator and the spark plug body.
Electrical test
1. Screw the spark plug into the socket on the stand and tighten it to the torque specified above.
2. Adjust the gap between the arrester electrodes to 12 mm, which corresponds to a voltage of 18 kV, and then use the pump to create a pressure of 6 kgf/cm².
3. Place the high voltage lead tip on the spark plug and apply high voltage pulses to it.
4. If a full spark is observed in the eyepiece of the stand, then the spark plug is considered excellent. If sparking occurs between the electrodes of the spark gap, then the pressure in the device should be reduced and the pressure at which sparking occurs between the electrodes of the spark plug should be checked. If it begins at a pressure below 3 kgf/cm², then the spark plug is defective.
5. Several sparks on the spark gap are allowed. If there is no spark formation on the spark plug and on the spark gap, then it must be assumed that there are cracks on the spark plug insulator and that the discharge occurs inside, between the mass and the electrodes. Such a spark plug is rejected.