What effect does changing the spark plug gap have?
Outstanding HDF Member
Joined: Jan 2011
Posts: 2,590
Likes: 31
From: Western Illinois, land of bad roads, and corrupt politicians
When you consider, most people use either those bent loop wire, or ramp gauges.... it really doesn't matter. Neither are accurate.
If you want accuracy, use a "feeler" gauge.
If both plugs are the same, and within the suggested range, then you're good. The important part is that both plugs match.
If you want accuracy, use a "feeler" gauge.
If both plugs are the same, and within the suggested range, then you're good. The important part is that both plugs match.
Sorry to say chaps, in the real world it's not going make difference," I did this" or "I did that" "and it seems to pull harder" etc etc is only an opinion, the only way you are going to tell if it makes any difference,is to put the bike on a dyno before and after any mods are done, and I bet you a pint the difference in the plug gap tolerence would be immeasurable on a dyno test.
Elite HDF Member
Joined: Nov 2010
Posts: 3,846
Likes: 171
From: Simi Valley, CA
Sorry to say chaps, in the real world it's not going make difference," I did this" or "I did that" "and it seems to pull harder" etc etc is only an opinion, the only way you are going to tell if it makes any difference,is to put the bike on a dyno before and after any mods are done, and I bet you a pint the difference in the plug gap tolerence would be immeasurable on a dyno test.
To say you can feel the difference in the seat of your pants... Not a chance. It's all in your head if you do think you feel a difference. Ever take your car or bike for a ride just after you've spent hours detailing it - It feels like it runs better right? I know mine feels like it does. But that's impossible, it's simply in my head.
And for the tighter gap to make the plugs last longer - that's a myth also. The edges of the electrode get rounded off from use. Regardless of the gap, as the electrode edges lose their sharpness the plug's performance degrades proportionately. The crispest spark occurs from a very sharp edge like that found on a brand new plug.
Last edited by 2black1s; Nov 20, 2011 at 06:36 PM.
Outstanding HDF Member
Joined: Jan 2010
Posts: 2,916
Likes: 31
From: earth
Sorry to say chaps, in the real world it's not going make difference," I did this" or "I did that" "and it seems to pull harder" etc etc is only an opinion, the only way you are going to tell if it makes any difference,is to put the bike on a dyno before and after any mods are done, and I bet you a pint the difference in the plug gap tolerence would be immeasurable on a dyno test.
Doesnt the same theory apply to your suggestion
This is what I would tend to agree with. While theoretically you can argue many of the points presented in this thread, in the real world any benefit is gonna be negligible, and certainly not measureable except possibly in a tightly controlled laboratory environment.
To say you can feel the difference in the seat of your pants... Not a chance. It's all in your head if you do think you feel a difference. Ever take your car or bike for a ride just after you've spent hours detailing it - It feels like it runs better right? I know mine feels like it does. But that's impossible, it's simply in my head.
And for the tighter gap to make the plugs last longer - that's a myth also. The edges of the electrode get rounded off from use. Regardless of the gap, as the electrode edges lose their sharpness the plug's performance degrades proportionately. The crispest spark occurs from a very sharp edge like that found on a brand new plug.
To say you can feel the difference in the seat of your pants... Not a chance. It's all in your head if you do think you feel a difference. Ever take your car or bike for a ride just after you've spent hours detailing it - It feels like it runs better right? I know mine feels like it does. But that's impossible, it's simply in my head.
And for the tighter gap to make the plugs last longer - that's a myth also. The edges of the electrode get rounded off from use. Regardless of the gap, as the electrode edges lose their sharpness the plug's performance degrades proportionately. The crispest spark occurs from a very sharp edge like that found on a brand new plug.
Seasoned HDF Member
Joined: Sep 2009
Posts: 17,138
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From: SE Michigan
Extreme HDF Member
Joined: Jun 2011
Posts: 14,731
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From: Mountain Top, Alabama
I'm sure a lot of considerations were taken to arrive at the recommended gap range of
.38 -.43 My recommendation would be to set them to the low to middle of these settings if you plan to run them the full service interval, the gap will increase with wear, but should stay within range. For shorter intervals, I would say run anywhere in the range you like, but I would pull and check plug condition following a few miles of your normal ride patterns (stop and go, highway, whatever).
In a mostly stock motor, You may not notice much change however.
.38 -.43 My recommendation would be to set them to the low to middle of these settings if you plan to run them the full service interval, the gap will increase with wear, but should stay within range. For shorter intervals, I would say run anywhere in the range you like, but I would pull and check plug condition following a few miles of your normal ride patterns (stop and go, highway, whatever).
In a mostly stock motor, You may not notice much change however.
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Cruiser
Joined: Dec 2008
Posts: 191
Likes: 2
From: At Work
Indexing is a complete waste of time. Think about this. The intake valve is open on the down stroke of the piston. At the bottom of the stroke the intake valve closes. As the piston comes up the entire fuel/air charge is swirling around in the cylinder. As the piston comes to the top, the charge is compressed into a small area and completely surrounding the spark plug. Then the spark plug fires. It will not make a bit of difference to have the gap pointed at the intake valve at this point of the cycle when the charge is no longer entering the cylinder. On these engines, it will make no difference in performance to have the plug gapped at either end of the tolerances.
