- Joined
- Nov 7, 2007
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- Location
- Antelope Valley CA
- First Name
- Scott
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- Brown
I haven't indexed my spark plugs an my bikes for quite a number of years, but I used to as it can make your plugs ignite the incoming fuel mixture better, improving your gas mileage and performance depending on the shape of the combustion chamber and the placement of the spark plug in the combustion chamber.
To index a spark plug, you mark a line on the the porcelain with a black marker in line with the side electrode, then screw the plug into the head and tighten it down to spec and observe the relationship of the mark to the intake valves, as you want the side electrode to be facing away from the intake valves and the incoming fuel mixture. The logic behind indexing your plugs is that you don't want the side electrode shielding the spark from the incoming fuel mixture.
Sometimes you'll luck out and have the side electrode facing away from the intake valves and don't have to make any adjustments, but if it doesn't you remove the plug and place a copper washer on over the threads on the plug which will make it lock up in a different position to the intake valve. I still have a bunch of different thickness copper washers from Moroso, and to accurately determine just how thick a shim to place on the plug to get it to lock up in the right position, all you have to do is determine the approximate degree that the plug needs to be rotated, and then using the pitch of the thread on the spark plug you are using, you can calculate the thickness of shim to use to effect the change in the angle of rotation to get the side electrode to line up where you want it.
So on a 14mm spark plug with a 1.25mm pitch, which equates to .050 of movement per turn, if you needed to have the plug lock up 45 degrees farther in rotation you would use a .012 thick washer.
I used to do this a lot on my older Harleys as it was easy to see the alignment mark on the side of the plugs. On the Bandit with it's plugs recessed way down in the head which will keep you from seeing the alignment mark on the plug, you would have to carefully place the alignment mark on the spark plug socket extension.
Summit Racing still sells several different brands of indexing washers, and this winter when I do a valve clearance inspection, throttle body sync and install new plugs, I may just for giggles index the plugs on my Bandit. You can also do a search on the internet and find all sorts of info about the benefits of indexing your plugs.
http://www.summitracing.com/parts/MOR-71900/
To index a spark plug, you mark a line on the the porcelain with a black marker in line with the side electrode, then screw the plug into the head and tighten it down to spec and observe the relationship of the mark to the intake valves, as you want the side electrode to be facing away from the intake valves and the incoming fuel mixture. The logic behind indexing your plugs is that you don't want the side electrode shielding the spark from the incoming fuel mixture.
Sometimes you'll luck out and have the side electrode facing away from the intake valves and don't have to make any adjustments, but if it doesn't you remove the plug and place a copper washer on over the threads on the plug which will make it lock up in a different position to the intake valve. I still have a bunch of different thickness copper washers from Moroso, and to accurately determine just how thick a shim to place on the plug to get it to lock up in the right position, all you have to do is determine the approximate degree that the plug needs to be rotated, and then using the pitch of the thread on the spark plug you are using, you can calculate the thickness of shim to use to effect the change in the angle of rotation to get the side electrode to line up where you want it.
So on a 14mm spark plug with a 1.25mm pitch, which equates to .050 of movement per turn, if you needed to have the plug lock up 45 degrees farther in rotation you would use a .012 thick washer.
I used to do this a lot on my older Harleys as it was easy to see the alignment mark on the side of the plugs. On the Bandit with it's plugs recessed way down in the head which will keep you from seeing the alignment mark on the plug, you would have to carefully place the alignment mark on the spark plug socket extension.
Summit Racing still sells several different brands of indexing washers, and this winter when I do a valve clearance inspection, throttle body sync and install new plugs, I may just for giggles index the plugs on my Bandit. You can also do a search on the internet and find all sorts of info about the benefits of indexing your plugs.
http://www.summitracing.com/parts/MOR-71900/