Spark Plug Indexing
What is Spark Plug Indexing, why should I care and how do I do it?
In short, spark plug indexing is the process of setting the open end of the electrode toward the gas/air mixture to achieve a better, more consistent burn.
Here is how to achieve this:
First of all, spark plugs, and the plug inserts in the engine head, have threads beginning at any random point in a 360 degree cycle. The thread begins wherever the machine or tool begins the cut; so, unless the outer part of the plug is marked you cannot tell where the electrode is pointed once the spark plug is installed in the head.
Oh, by the way, the electrode is the appendage that extends down from the plug and then makes a 90 degree turn to form the spark plug "gap". Use a magic marker to index or mark the plug on the porcelain or socket area above and in line with the backside of the electrode.
Now, you will know exactly where the open "gap" part of the electrode is pointed when the plug is screwed into place.
In order to have consistency, and also to know how to measure, in advance, the thickness of the indexing washer required to position each plug correctly, once installed, the torque used to tighten it down is 10 foot pounds. I know, I know your book says to tighten the plugs down to what-ever ft.-lbs.. but, the indexing washers reduce this to 10 ft-lb.. Long time mechanics can tell these torque ratings by "feel" but you should use a tool called a torque wrench. If you plan to do backyard or weekend wrenching, this tool is a wise investment.
Purchase a package of different thickness spark plug crush washers. These are the washers that come with every plug, but they are made especially for indexing purposes. Mark the plug to be indexed with a marker in the appropriate place described above and screw it in to the mandatory ten ft.-lb.. Observe the indexing mark and visually calculate how many degrees counterclockwise it would take to position the spark plug correctly.
Remove the plug and position the correct size crush washer, utilizing the following information:
.043 washer rotates the plug counterclockwise by 105 degrees.
.054 washer rotates the plug counterclockwise by 210 degrees
.064 washer rotates the plug counterclockwise by 315 degrees.
Reinstall the plug at 10 ft.-lb.. using only the new washer.
Did we forget something? Oh yeah, what do you index the open electrode towards, Well, it depends on what kind of bike you have. On most Japanese bikes you just face that index toward the intake valve.