Here's another quick tech mod that will add 3 HP to your XR1200...
Well, maybe not!! But it's one of those fanatical things that guys like to do,
and I'm just in the habit of doing it.
Indexing your spark plugs points the spark gap toward the center of the combustion
chamber, and/or slightly toward the intake valve. In theory this sets up a better ignition wavefront for a more complete
burn of the gases. In a modern twincam the liklihood of this making a difference is very small, as opposed to in some
of the older bikes that had asymmetrical combustion chambers.
While spark plug choice is almost as contentious as oil choice, I've never found a
significant difference in changing plug types or brands. I've tried platinum plugs, split fire plugs, etc. etc. in the
twincam and the only thing that has really induced a performance difference is changing the spark plug gap. (Narrowing
the gap slightly acts like advancing the timing a couple of degrees.) But as for plug type, I've never seen noticeable
differences on the dyno. But then that's a dangerous claim to make, since some guys swear their plug type change added
HP, throttle snap, and/or acceleration. Likewise, I can't say I've seen any noticeable change in indexing the plugs
on a modern twincam - but I still do it.
Here is how...
Ideally, when threaded into their cylinder heads, the plug's electrode gap will point toward
the center of the cylinder. But -the orientation of the electrode on a spark plug varies in relation to the threads,
and even if a particular plug type were always produced exactly the same, the threads in the plug holes in the heads vary.
So, some spark plugs will just naturally orient better in a cylinder than others.
In order to help align the spark gap, one can buy spark plug "indexing" washers.
These washers come in different thicknesses, and will let you change the direction that the gap points toward,
when the plug is tightened into the cylinder head. Here are one brand of indexing washers...
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These Moroso indexing washers come in three thicknesses. The idea is that each washer
thickness will back the spark plug up about 1/3 of a rotation. To index the plug, one
- first marks the direction of the electrode opening on the side of the plug so
that it can be observed when the plug is inserted,
- installs the spark plug in its cylinder and torques it to spec (Moroso
calls for 10 ft-lbs although I usually use 12 ft-lbs, and HD calls for 12-18 ft-lbs).
- checks the marks on the spark plugs to see where the plug gap is pointing
- inserts a washer under the plug to point it in the proper direction, or the plug is
exchanged for one that naturally orients in the desired direction.
Moroso gives a chart on the back of the package that tells how many degrees each thickness of
washer is supposed to rotate a spark plug, but I find that actual plug rotation differs. I usually try the washer
that should work and then experiement with others to see if they produce better results.
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In the above picture I have marked a spark plug and test fit it in the rear cylinder head.
I usually put a single line on the plug insulator in the direction of the gap, and a double line 180 degrees out, on the back
side. This way I can easily see where the plug gap is pointing. In this case, this plug is pointing
90 degrees out, toward the rear of the bike. Ideally, a plain copper colored washer should bring the gap back 105 degrees,
pointing it almost perfectly toward the intake valve.
Now the front cylinder. First I test fit a spark plug and you can see that this one
pointed toward the rear of the bike and outside edge of the cylinder. Not at all ideal! This plug just happens
to align in the rear cylinder a little better than it does in the front, so I tried a different spark plug in the front
cylinder. (I usually buy a half dozen plugs at a time, to have a selection to try from.)
Now, with the spark plugs properly indexed I'll take the bike back out on the road.
Since I've been so diligent in my work, I am sure the throttle will snap, and the front wheel will rise off the ground as
a result of my work - oh wait, it did that before...
Oh well, I feel better!!
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In the above picture I have added an indexing washer and the plug gap now points directly
toward the middle of the combustion chamber. Although this should have taken a plain copper washer, that did not produce
the best results. I experimented, and one of the other washers did work well. Voila!!
|Front Plug - Different Plug
Just out of pure luck, it turned out that the next spark plug that I grabbed oriented almost
perfectly in the front cylinder without a washer. All done!!