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Spark Plug Installation & Maintenance - from Cyclepedia
SAFETY FIRST: Protective gloves and eyewear are recommended at this point.
Remove the spark plug cap from the spark plug.
Some motorcycles use what is commonly called a stick type ignition coil that fits directly onto the spark plug.
Use compressed air to blow out any dirt or debris that may fall into the combustion chamber when the spark plug is removed. This is very important to prevent engine damage.
NOTE: Always wear safety glasses when using compressed air and never point it directly at yourself or anyone else.
Use a spark plug socket and ratchet to remove the spark plug from the cylinder head, you may need to use an extension as well. There are currently three size spark plug socket sizes used, 5/8″, 18 mm and 13/16″. Spark plug sockets differ from ordinary deep well sockets in that they have a rubber insert to hold the spark plug in the socket for easier removal and installation.
Inspect the spark plug porcelain for cracks or damage. Check the electrode for wear, fouling or deposits. The center and ground electrodes should have nice square edges. If they appear rounded, replace the spark plug. The spark plug porcelain insulator nose should be a light tan color, which can indicate how your engine is performing. For example, if the spark plug nose is white the engine may be running too lean, if the spark plug nose is dark the machine may be running too rich.
Use a flat feeler gauge or a wire gauge to measure the gap between the ground electrode and center electrode. To change the gap, carefully bend the ground electrode.
Install the spark plug and tighten it to the torque specification in your service manual. Another way of tightening a new spark plug properly is to install it hand tight, put a wrench on it and turn it another 1/2 to 3/4 of a turn. It is common (and damaging) for people to over-tighten the spark plug. Remember that the threads in the cylinder head are soft aluminum and can be easily stripped. If installing a used spark plug where the sealing washer has already been crushed, install the spark plug hand tight and turn it 1/8 to 1/4 of a turn with a wrench. Re-install the spark plug cap or the stick-type ignition coil.
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