Cracked ceramic plug issues

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66Valiant528

66Valiant528

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Started up the Valiant this weekend for the first time this year. Looking for issues I found another spark plug wire shorting out the end of the boot to the hex on the plug. Pulled the plug and the ceramic is cracked. This is the 3rd AR3910 plug that has done this. Seems odd. WTF. Have and MSD7 and a pro power coil 13.8 to 1 race gas . Why does this happen? What are these flakes/dark spots on the ceramic?

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I have cracked brand new plugs while installing them! Need to keep the socket and extension as straight as possible if that's the issue.
 
69FBCuda said:
I have cracked brand new plugs while installing them! Need to keep the socket and extension as straight as possible if that's the issue.
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And use a spark plug socket with a rubber insert.
 
I thank you both but this arc has only started recently. I am always very careful with the ceramic and if there's ever a question I replace it. It's difficult enough getting at the plugs.as far as a rubber boot inside the socket sometimes I find it very difficult to get the socket off. Usually I don't have the luxury of a full size socket. Had to make a handy plug socket. I can't believe I damaged 3 plugs.3/4 swivel gear wrench does the trick.

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Are you using dielectric grease in the plug boots? I've have my MSD 7AL2 make the spark jump through boot when I didn't use the dielectric grease.
 
Demonracer said:
Are you using dielectric grease in the plug boots? I've have my MSD 7AL2 make the spark jump through boot when I didn't use the dielectric grease.
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I usually do and made sure this plug/wire got some. That was my initial plan to grease it and see if that took care.of it ,but then I saw the crack.thanks
 
66Valiant528 said:
I usually do and made sure this plug/wire got some. That was my initial plan to grease it and see if that took care.of it ,but then I saw the crack.thanks
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I just read an article on Engine Labs (I think that's where it was) about Ford switching to 12 mm diameter plugs. One of the things with that plug they developed was they used a different end on the plug (IIRC they called it a VW end) and that allowed then to make the porcelain of the plug longer. The upshot of the longer porcelain was to reduce/eliminate fracturing the porcelain.
 
I think they mean the end of the plug is a threaded post. I was thinking about how some of the late model engines use a smooth ceramic as opposed to the ribbed style that the 3910 plug is. Well I'll see how long this set works and if I get another failure I may try a different brand. AR3910 is what the engine dyno people suggested. Cold plug...
 
The purpose of the ribbing is to lengthen the distance from the plug terminal to the metal body. If there are conductive contaminants of the surface of the porcelain, the spark can short out [ path of least resistance ]. Making this distance longer reduces the chances of this happening.....
 
So I guess ribbed has more surface area distance than the smooth bodied plugs
 
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