INSPECTION

INSPECTION

Fig. 1: A normally worn spark plug should have light tan or gray deposits on the firing tip

Fig. 2: A carbon fouled plug, identified by soft, sooty, black deposits, may indicate an improperly tuned vehicle. Check the air cleaner, ignition components and engine control system

Fig. 3: A variety of tools and gauges are needed for spark plug service

Fig. 4: A physically damaged spark plug may be evidence of severe detonation in that cylinder. Watch that cylinder carefully between services, as a continued detonation will not only damage the plug, but could also damage the engine

Fig. 5: Checking the spark plug gap with a feeler gauge

Fig. 6: An oil fouled spark plug indicates an engine with worn piston rings and/or bad valve seals allowing excessive oil to enter the chamber

Fig. 7: Adjusting the spark plug gap

Fig. 8: This spark plug has been left in the engine too long, as evidenced by the extreme gap — Plugs with such an extreme gap can cause misfiring and stumbling accompanied by a noticeable lack of power

Fig. 9: If the standard plug is in good condition, the electrode may be filed flat — CAUTION: do not file platinum plugs

Fig. 10: A bridged or almost bridged spark plug, identified by a build-up between the electrodes caused by excessive carbon or oil build-up on the plug

Compare the condition of the spark plugs to the plugs shown in the accompanying photos. It should be remembered that any type of deposit will decrease the efficiency of the plug. If the plugs are not to be replaced, they should be thoroughly cleaned before installation. If the electrode ends of the plugs are worn or damaged and if they are to be reused, wipe off the porcelain insulator on each plug and check for cracks or breaks. If either condition exists, the plug must be replaced.
If the plugs are judged reusable, have them cleaned on a plug cleaning machine (found in most service stations) or remove the deposits with a stiff wire brush.
Check the plug gap on both new and used plugs before installing them in the engine. The ground electrode must be parallel to the center electrode and the specified size wire gauge should pass through the opening with a slight drag. If the center or ground electrode has worn unevenly, level them off with a file. If the air gap between the two electrodes is not correct, open or close the ground electrode, with the proper tool, to bring it to specifications. Such a tool is usually provided with a gap gauge.