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Discussion Starter · #1 ·
Checked my spark plugs today, and found something interesting. Several threads of the plug run down into the cylinders.

This is great for flame front, but it looks like my rear exhaust valve was grazing the back side of the electrode. Also, there is enough carbon build up and heat on the threads that galling was starting to occur. The spark plugs had to be worked a bit to come out. As it was, one thread in my rear plug hole was damaged.

It is worth pulling your plugs and taking a look at the threads and electrode. If they are tough to get out, don't force them. They can be worked back and forth, and/or some penetrant, carb cleaner, or aero kroil can be used.

Some people are not fans of anti-seize on plugs because of the risk of poor electrical conduction, but I'm putting a touch on the leading edge of my plug threads, to try to avoid future thread damage in the heads.

Just a thought...
 

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Glad someone brought up spark plugs. I've been using NGK DCPR7EIX Iridium spark plugs in all bikes I've owned recently. My CRF450 Honda came with 'em and I've raced Them every weekend for a year on the same sparkplug. I tried then in my Superglide and they were super. I've put them in friends bikes and not told them and they remarked on how the bikes ran. The biggest comment was on throttle responce even on older carburator bikes. Adrenalin just started carring them. Give em a try, you'll like 'em for sure. The plugs do extend a bit but that is an advantage. Mark the plug oposite the electrode on the open side and shim the plug so the open side is toward the combustion chamber. This is an old tuner trick to assist in better ignition on a single plug head. :angel: Later,
 

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spark plugs

On Matt's recommendation-I changed from stock to the NGK DPR9EIX these are great non fouling plugs that seem to run and accelerate a bit smoother. I have not noticed any interference with the valves. I use permatex anti seize per recommendation of the service manual and torque them to spec. I did notice that there was no anti seize present on factory initialy installed plugs despite their requirement upon plug replacement.
 
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Discussion Starter · #4 ·
I installed the NgK plugs (8) the engine seem to run a little hotter anyone see a difference in engine temp with the NGK plugs ? No real noticeable performance change from the stock plugs on my XR.
 

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Haven't seem any increase in heat. The plugs I'm running are hotter than the ones Mort is running. The number in the plug number is the heat range so the "9's" are two stages colder than the "7's". Mine are burning perfect. The "heat" rating is for refrance in tuning and not the actual heat of the engine. Cooler plugs can run leaner mixtures and hotter richer. I have used SERT to richen for cooler overall temp. Funny thing if you go on the NGK site it recommends the "7's" for Sportsters and the big bikes and have used them in both and they work awesome. :scooter: Later,
 

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hmmmmm

Verrry interesting....couple of questions...

Are we seeing 3 different heat ranges in this thread - 7 for FB, 8 for R Moore, 9 for Mort? Or, more likely, have I misunderstood?

Phaed, would it be possible or advisable to use an extra crush washer on these plugs?

FB, I been riding and racing as long as you (but I was never as fast [:)]) I've never heard of "shimming" a plug. Details pleeeeze.
 

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It is better to "shim" with a flat washer above the crush washer. The shimming is to direct the open part of the center electrode toward the combustion chamber instead of of being "shielded" by the ground strap. It's probably not that big of a deal with the new ignition systems. I asked my Screaming Eagle tech why my spark plugs were marked and that was the answer. The larger the piston the harder it is to light the fuel with one spark plug I guess. :whistling: Later,
 
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Discussion Starter · #8 ·
Verrry interesting....couple of questions...

Are we seeing 3 different heat ranges in this thread - 7 for FB, 8 for R Moore, 9 for Mort? Or, more likely, have I misunderstood?

Phaed, would it be possible or advisable to use an extra crush washer on these plugs?

FB, I been riding and racing as long as you (but I was never as fast [:)]) I've never heard of "shimming" a plug. Details pleeeeze.
It is not necessarily advisable to shim the plug to back it out a few threads. We did a quick measurement and the plug could be shimmed .060 to .080 to decrease its depth - but decreasing its depth will back the flame front out of the cylinder, which could hurt combustion. Better to check the plugs first to see if there is any interference problem.

As for "indexing" - or aligning the spark gap with the center of the cylinder, or perhaps slightly toward the air fuel flow from the intake valve - I do it in my other bike and am going to start in this bike. But not to increase performance. In a Twincam, if it makes a difference it is so subtle as to not be noticeable in a dyno. The head chamber on the newer stock heads just doesn't appear to be very sensitive to this. I've heard guys say they can pick up a quarter or even half a horsepower by doing this, but that's about the equivalent of noise on the dyno. The reason I index on my softail is because I'm anal. And the reason that I'm going to index on this bike is because the valves are so close to the spark plug that rotating the electrode into the middle of the path will gain some clearance.

Personally I don't index with washers. (Although you can buy indexing washers in various thicknesses.) I just buy a box of plugs and mark them and test fit them. Due to manufacturing tolerances some will index well, and some won't. If you want to try this, check each plug in both holes. Plugs that don't index well in one cylinder may line up well in the other. Most people could care less about indexing, so I just pass off my "bad" plugs to my buddies...
 

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Phaedrus, Very good explination if indexing. It is expensive to not shim the Iridium since they come with only 4 per box but I've only had to shim one of them. I'm also very glad to see I'm not the only anal forum member. :clap: Later,
 

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spark plugs

I double checked with Matt prior to installing the 9's and he said there is an uncorrected error in Ngk's application guide. He also said he has been running the Iridium 9's for quite some time with excellent results in all his Buells and XR's including his personal bike. I fully agree with Matt. I noticed a slightly smoother idle and slight improvement in throttle response right after the installation about 1,000 miles ago. I use Permatex anti-sieze and I torque the plugs to approx 20NM and no problem getting them in or out. As long as their is no fouling-which I have not experienced-colder is usually safer. The NGK part number here in the states is #5545 (DPR9EIX-9) ask for the non-threaded top post. I ordered mine from Advance Auto Parts. Around $8 a plug. By the way, I would like to take a moment to mention that Matt has been fantastic in helping me with the mods on my bike. His is patient, honest, informative, and has provided fantatstic customer service. I would not be nearly as happy with my XR without his advice and parts. This forum has been a great help to me as well. Thanks to all of you for getting me completely addicted to riding and even just looking at my XR!!!!!!! My wife said she wishes I would look at her the way I look at my XR-so I told her all she has to do is sit on it!! (partially undressed of course) Mort
 
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Discussion Starter · #11 ·
Phaedrus, Very good explination if indexing. It is expensive to not shim the Iridium since they come with only 4 per box but I've only had to shim one of them. I'm also very glad to see I'm not the only anal forum member. :clap: Later,
Oh come on Billy you just love me 'cause I'm not only anal but some would describe me as "big boned"!

And I'm not trying to dis the benefits of indexing. For a racer a 1/4 or 1/2 HP of essentially free power would be big.

But my personal belief is that the addition of this power is likely to be seen as the last addition on a well-tuned HD, and not the first on a production HD v-twin. Even I "feel" the improvement in every change I make, well not really. I generally don't count anything as real until it changes my ET, dyno numbers, or fuel efficiency. And after a good bit of dyno time, and comparison with some actually very good known tuners, I've never seen a difference in measured performance on a stock or mildly modified HD using different plugs. The cheap HD 6r12's for instance, actually seem to run better than the triple platinum wonders in the Big Twins, 'cause they deliver the same performance and don't throw codes.

I do think there is an issue with the ignition path on the XR1200 because of some misfire indications that we were seeing yesterday at WOT and high RPM on the dyno pulls, but I don't know that a plug swap will cure this.

Hey, but winning is all about psychology, so if the change gives the rider the mental edge.... :)

jmho
 

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The indexing of spark plugs debate has been going on for many years. In fact you can buy special indexing washers in various thicknesses with indexing marks on them. There have been plenty of Dyno test's in the major automotive magazines over the years with mixed results. Some combustion chamber designs respond more than others but in all cases the gains (if any) were tiny.
As far as anti size goes, being in the ignition business, we have looked at this and our testing has come to the conclusion that there is PLENTY of ground contact through the washer or seat of the plug and it is nothing to worry about. JMHO
 
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