Spark plug change

[Chrisj CMA]

Some rain today delayed some of my work. So I made use of the time by changing out and indexing the spark plugs on the Cobra bike. The old ones looked great and light brown. But it’s been around 50,000 miles so out they went. Auto Zone only had six of the Valkyrie spark plugs. I usually buy 8 so I have choices when indexing. But, I got lucky and found a hole that worked for each of the six I had 

[sixlow]

Now that's something I haven't done, Please remind me of the gap orientation Jeff, how should they aim?

[Chrisj CMA]

Now that's something I haven't done, Please remind me of the gap orientation Jeff, how should they aim?

I’m not as picky as the mechanic that taught me about indexing plugs. On our Valkyries because of the flat cylinder and the angle of the spark plug. If the spray is at 12 O’clock as looking at the installed plug then it’s spraying against the wall of the cylinder. I try to get them all at six O’clock. But anything between 4 and 8 is ok with me. I mark the porcelain with a sharpie and then I can see where it lands

[WintrSol]

Interesting article on the subject: https://www.enginelabs.com/news/getting-ignition-spark-plug-indexing-101/
And another one that disputes that one: https://www.hotrod.com/articles/how-to-index-spark-plugs/

[gordonv]

How do you alter their alignment?

Tighten the plug, change the hole, or add washers/spacers?

[Chrisj CMA]

How do you alter their alignment?

Tighten the plug, change the hole, or add washers/spacers?

I change a plug to a different cylinder and this time I was able to juggle them so six plugs found an acceptable home

[WintrSol]

How do you alter their alignment?

Tighten the plug, change the hole, or add washers/spacers?

The position of the ground arm is kind of random, relative to where the spark plug actually gets tight, so you just note where each stops and juggle them around until it's good enough. There are washer sets available, but they keep the plug out of the chamber a little bit, of course.

[Chrisj CMA]

How do you alter their alignment?

Tighten the plug, change the hole, or add washers/spacers?

The position of the ground arm is kind of random, relative to where the spark plug actually gets tight, so you just note where each stops and juggle them around until it's good enough. There are washer sets available, but they keep the plug out of the chamber a little bit, of course.

Exactly and as long as the spray is down towards the valves and not up against the cylinder wall it’s good enough for me. The mechanic that taught me about it would insist the spray aimed right at the intake valve. I’m not even sure what clock position that would be for a Valkyrie.

[jnicks01]

Looking at my repair manuals, it appears the intake valve is about 2 o'clock, If up is 12 o'clock.  Would that change anything on the 4 to 8 positioning?  This is a learning experience for me, so please enlighten my curiosity. 

[Chrisj CMA]

Looking at my repair manuals, it appears the intake valve is about 2 o'clock, If up is 12 o'clock.  Would that change anything on the 4 to 8 positioning?  This is a learning experience for me, so please enlighten my curiosity.  

No, if you think about the angles anything near 12 is spraying at the cylinder wall

[h13man]

Basically having the open side of the spark plug pointing toward the bottom (6 o'clock) of the combustion chamber +/- 60 degrees? I throw in another kicker though more $$, Iridium plugs though shimming could be factored in due to cost. Why I say this, my bike run's a little rich but no loss of power or mpg's, with stock NGK's it would foul a plug every time just right over the 10,000 mi. (2x) mark as per OEM change spec. I went to iridiums and I'm @ 11,300 mi. w/o any issue but using the choke isn't necessary anymore only in the spring start up. Yes I could be needing a fuel system tuneup but until then I think this might be a plus to performance regardless. Thanks for bringing this up. 

[jnicks01]

Looking at my repair manuals, it appears the intake valve is about 2 o'clock, If up is 12 o'clock.  Would that change anything on the 4 to 8 positioning?  This is a learning experience for me, so please enlighten my curiosity.  

No, if you think about the angles anything near 12 is spraying at the cylinder wall

Diagram helps.  Thanks.  Now I get a reason to go into the barn and see what I've got them at.

[..]

Looking at my repair manuals, it appears the intake valve is about 2 o'clock, If up is 12 o'clock.  Would that change anything on the 4 to 8 positioning?  This is a learning experience for me, so please enlighten my curiosity.  

No, if you think about the angles anything near 12 is spraying at the cylinder wall

Diagram helps.  Thanks.  Now I get a reason to go into the barn and see what I've got them at.

Me too. Why not give it a try?

[Chrisj CMA]

It’s not going to be a huge improvement. I notice easier starts and a smooth idle. Besides that it will run pretty much the same

[WintrSol]

Looking at the photo at the top of page 8_13 of the service manual, it appears the plug is near the center of the chamber, and very little, if any, benefit would be obtained, per the second article I linked above. Still, you can figure the rough clock position from that photo. I'm not going to bother.

[sandy]

The flaw I see in this subject is that spark doesn’t spray. It’s a ZAP between the electrodes. With compression and proper fuel/air ratio, no difference is made on plug indexing. Sometimes I think my truck runs better when I change the oil but I know better.

[Chrisj CMA]

The flaw I see in this subject is that spark doesn’t spray. It’s a ZAP between the electrodes. With compression and proper fuel/air ratio, no difference is made on plug indexing. Sometimes I think my truck runs better when I change the oil but I know better.

Well like I said it’s not an earth shattering difference . But there are tons of people that take the time. I notice easier starts and a smoother idle so I will continue doing it. I’m sure your bike will run just fine if you don’t

[WintrSol]

No, the spark doesn't spray, but the flame front kind of does. In poorly designed combustion chambers, if the open side of the plug pointed mostly at the wall, instead of into the middle, the flame would have to bounce off that wall before returning to the rest of the mixture, which is probably why clocking made a difference. Looking at photos of our heads, I don't believe that effect, if present at all, has significant impact on the flame travel. It appears our plugs are in a small well, fairly close to, and aimed at, the center of the chamber, so the flame, started in any primary direction, would beam almost directly into the heart of the chamber.

[Chrisj CMA]

No, the spark doesn't spray, but the flame front kind of does. In poorly designed combustion chambers, if the open side of the plug pointed mostly at the wall, instead of into the middle, the flame would have to bounce off that wall before returning to the rest of the mixture, which is probably why clocking made a difference. Looking at photos of our heads, I don't believe that effect, if present at all, has significant impact on the flame travel. It appears our plugs are in a small well, fairly close to, and aimed at, the center of the chamber, so the flame, started in any primary direction, would beam almost directly into the heart of the chamber.

Not to be argumentative but I looked up a picture of the Valkyries head/ combustion chamber. Yes the spark plug is in a cup like depression of sorts but the area that would correspond to say something between 4&8 O’clock is more open. So I stand by suggestions. Index them near the six for the best flame shot. Guys, this is not very important. Your bike will be just fine if you don’t index the plugs. It’s just a fun cheap way to maybe tweek the old gal to run a slight bit better

[Chrisj CMA]

Want to determine the benefit of indexing?  Buy a large quantity of spark plugs of the same type.  Gap all the same.  

Then:

1. Install 6 with random orientation and dyno the bike.  

2. Install 6 new plugs in the preferred indexed position and again dyno the bike.  

3. Install another set of 6 new plugs opposite the orientation of step 2, and dyno.

Comparing the results would give you some idea if indexing makes more power.  Of course, you would have to run the experiment multiple times for the most reliable results.

I never expected a hp jump. Like I said. I think my bike starts easier and idles smoother. No further tests needed.

[WintrSol]

No, the spark doesn't spray, but the flame front kind of does. In poorly designed combustion chambers, if the open side of the plug pointed mostly at the wall, instead of into the middle, the flame would have to bounce off that wall before returning to the rest of the mixture, which is probably why clocking made a difference. Looking at photos of our heads, I don't believe that effect, if present at all, has significant impact on the flame travel. It appears our plugs are in a small well, fairly close to, and aimed at, the center of the chamber, so the flame, started in any primary direction, would beam almost directly into the heart of the chamber.

Not to be argumentative but I looked up a picture of the Valkyries head/ combustion chamber. Yes the spark plug is in a cup like depression of sorts but the area that would correspond to say something between 4&8 O’clock is more open. So I stand by suggestions. Index them near the six for the best flame shot. Guys, this is not very important. Your bike will be just fine if you don’t index the plugs. It’s just a fun cheap way to maybe tweek the old gal to run a slight bit better

In this system of measurement, what is 12? Toward the head/block surface or top of the head? Looking at the photo, it appears to me that the space between valves is orientated at about 8, relative to the spark plug position, if 12 is towards the intake runner, or top of the head. I should think this would provide the 'best' position, so ~8 would be the center of the optimum range.

[dconstruct55]

I was just contemplating a spark plug change so this post was very timely and enlightening. Thanks for all of the tips and thank you Jeff for posting!

[Chrisj CMA]

Well now I’ve seen two pictures of valkyrie heads that are way different one from the other. I’m not going to worry my bike is running like a scalded ape.  I do think all the plugs oriented down made a difference or maybe just that they are all the same.

On one picture the spark plug is in the center and I would think in that case the index is much less important. The other picture it’s in a triangle with the valves and a 4 to 6 O’clock position should be helpful

[Madmike]

If you want to experiment with the effects of using plug designs there are several options available.  

On the larger displacement (600CID per cylinder) natural gas engines we used plugs that had 4 electrodes.  Some of these engines had the plug right into the combustion chamber, others used a "pre-cup" design.

On these particular pre-cup design engines (these were >800CID/cylinder) the plug fired the pre-cup that had a port in the round bottom of it, the pre-cup was indexed so that when the flame came out the port it was directed to a specific area of the cylinder.  I was standing beside one of these running at full load one time when it started detonating.  It was a religious experience.  It ended by spitting a pre-cup into the turbo (rebuild cost $50K).

I did see videos one time showing how the flame front progresses across the piston as it burns.

NGK has a few designs of plugs available if you want to play    https://www.ngk.com/ngk-ground-electrode-designs

[Chrisj CMA]

Ok I figured it out. The head where the plug enters essentially in the center is the 1800. So anything from even 3 to six or  8 should be better than 9 to 12

[turtle254]

Ok I figured it out. The head where the plug enters essentially in the center is the 1800. So anything from even 3 to six or  8 should be better than 9 to 12

The pic I sent you was from my 1500

[Chrisj CMA]

Ok I figured it out. The head where the plug enters essentially in the center is the 1800. So anything from even 3 to six or  8 should be better than 9 to 12

The pic I sent you was from my 1500

The only pictures I’ve seen I found on line

[turtle254]

Ok I figured it out. The head where the plug enters essentially in the center is the 1800. So anything from even 3 to six or  8 should be better than 9 to 12

The pic I sent you was from my 1500

The only pictures I’ve seen I found on line

Check your email  ... I used the one on your profile

[h13man]

Well if the parts fische is right in its illustration, the plug hole is positioned @ 10 o'clock inside the head which would equal to 2 o'clock outside. So "8 o'clock is my final answer". 

https://www.servicehonda.com/oemparts/a/hon/506cb611f870023420a41720/cylinder-head

[Chrisj CMA]

Well if the parts fische is right in its illustration, the plug hole is positioned @ 10 o'clock inside the head which would equal to 2 o'clock outside. So "8 o'clock is my final answer".  

https://www.servicehonda.com/oemparts/a/hon/506cb611f870023420a41720/cylinder-head

After further study of the picture myself instead of using 4-8. I’m going to shift to from 7-10

Went to adjust them. #6 was already at 9 o’clock three others were at 8 o’clock. Switching the other two put one at 9 and the last one at 6. I can live with one a bit out from ideal

[h13man]

Went to FleaBay to see actual pic's, the plug comes into the head on both side's @ 10:30am position inside = 1:30pm outside.

[Chrisj CMA]

Went to FleaBay to see actual pic's, the plug comes into the head on both side's @ 10:30am position inside = 1:30pm outside.

No, it’s easy to get it backwards looking at a picture of the inside of the head. The intake is a direct shot from the outside at 9 o’clock

[Top Cat NJ]

The easiest thing has now become complicated. LOL I'm almost due for plugs and wires, I always do both, I'll give indexing a try.

[turtle254]

Everybody has to use the same 12:00 o'clock  position. Which is ?
Looking from the outside with the heads turned the same way .
I'm not sure which 12:00 o'clock were using?

[The emperor has no clothes]

I'm thoroughly convinced after following this thread, when it comes time for new plugs, I'm just putting in. Regardless of what time the clock says it is. 

[Chrisj CMA]

Everybody has to use the same 12:00 o'clock  position. Which is ?
Looking from the outside with the heads turned the same way .
I'm not sure which 12:00 o'clock were using?

Look at a clock (the old kind with hands.) See the 12 at the top. That’s the 12 o’clock position. Imagine the spark plug hole (right before screwing in the spark plug) is the perimeter of a clock face. 12 o’clock is at the same place (top).

The most efficient place for the spark plug “spray” to face would be 9 o’clock. But anything from 6 or 7 to 10 would be better than say 11-5

[Ricky-D]

The common practice indexing sparkplugs is to have the sparkplug gap facing directly to the intake valve.

That's what it is all about.

***

[Chrisj CMA]

The common practice indexing sparkplugs is to have the sparkplug gap facing directly to the intake valve.

That's what it is all about.

***

Yes that would be 9 o’clock

[h13man]

I'm thoroughly convinced after following this thread, when it comes time for new plugs, I'm just putting in. Regardless of what time the clock says it is. 

  Yep!

Maybe I can actually do a wheelie instead of slightly lifting the front end. All in all it's a good read of something I never knew that existed. 

[Chrisj CMA]

I'm thoroughly convinced after following this thread, when it comes time for new plugs, I'm just putting in. Regardless of what time the clock says it is. 

To each his own. You will have no Ill effects. Must of us have done it that way for years.  I know it is a little complicated for some.