Spark plug question

[Sonny]

I’ve researched this up and down the internet and can’t find anything that addresses the single black spot on my plugs. It’s not oil, it’s like a burned spot. I’ve tried hotter and colder plugs but still get this Mark. I’ve tried leaner and richer, same mark. Could this be caused by my motor home 440’s 452 heads with water jackets around the plugs cooling 3/4 of the perimeter? The pics below are of the same plug Autolite 23s taken after idle (not wot). Was running champion RV12YC but pinging was excessive, the 23s are better:

 

[HEMI-ITIS]

The only thing I could think of is to index the plugs,that might give you an even burn.

 

[Sonny]

The only thing I could think of is to index the plugs,that might give you an even burn.

Unfortunately my heads have a tapered seat. Not sure that’s possible.

 

[HEMI-ITIS]

Sure it is,just a PITA!!!

 

[66Satellite47]

I think that's a function of plug indexing and burn characteristics of the chamber.

 

[Photon440]

Unfortunately my heads have a tapered seat. Not sure that’s possible.

Tapered washers are available for indexing. https://www.jegs.com/i/JEGS/555/40356/10002/-1

 

[Sonny]

Tapered washers are available for indexing. https://www.jegs.com/i/JEGS/555/40356/10002/-1

I had no idea!!! Thanks!

 

[Sonny]

So I should try to align the burn mark 180 degrees from the strap?

 

[1967coronet]

I’ve researched this up and down the internet and can’t find anything that addresses the single black spot on my plugs. It’s not oil, it’s like a burned spot. I’ve tried hotter and colder plugs but still get this Mark. I’ve tried leaner and richer, same mark. Could this be caused by my motor home 440’s 452 heads with water jackets around the plugs cooling 3/4 of the perimeter? The pics below are of the same plug Autolite 23s taken after idle (not wot). Was running champion RV12YC but pinging was excessive, the 23s are better:
View attachment 986089 View attachment 986090 View attachment 986091 View attachment 986092

Have you swapped pistons for a different pin height ? If not, the pinging/detonation you mention while running the #12 champions would have me looking at the timing and distributor advance. Mabey you have bumped the compression and that makes this a non issue but if not that 7 .5.1 engine should not have a detonation problem. I am no pro at all but those plugs look lean to me.

 

[Sonny]

Have you swapped pistons for a different pin height ? If not, the pinging/detonation you mention while running the #12 champions would have me looking at the timing and distributor advance. Mabey you have bumped the compression and that makes this a non issue but if not that 7 .5.1 engine should not have a detonation problem. I am no pro at all but those plugs look lean to me.

I installed Keith black pistons that raised the compression ratio to 8.9.

 

[Sonny]

Have you swapped pistons for a different pin height ? If not, the pinging/detonation you mention while running the #12 champions would have me looking at the timing and distributor advance. Mabey you have bumped the compression and that makes this a non issue but if not that 7 .5.1 engine should not have a detonation problem. I am no pro at all but those plugs look lean to me.

Also note those pics are of one plug. My afr is barely 12 at cruise and wide open, idle is 13 based on my wide ban gauge. Maybe the gauge is lying to me?

 

[1967coronet]

I installed Keith black pistons that raised the compression ratio to 8.9.

Good to hear about the Keith Black pistons. I have never yet did that with my MH 440 still running low comp.
Even with your 8.9 it seems low for detonation but with the crap fuel we have now days anything is possible.
with the af meter that should be plenty of help, I just thought the plug looked lean, prob just me.
Have fun indexing hope it gets rid of your burn mark.

 

[66Satellite47]

Thinking about it, seems like a J12 was fairly hot back when we had "good" gas. Don't know how the Autolite 23's compare. IIRC the Champions & Autolites heat ranges didn't line up together very well. Maybe some distributor re-curving is needed for the pinging. In my iron head motors the burn pattern was never consistent around the porcelin.