8.1l spark plug cracking (again) and plug recommendations

[deputydog]

My W22 had a rough idle and was missing under load again so I started with the "check the wires" (replaced them with a spare set I had and no difference) so I pulled the plugs and found the outside insulator of #7 and #8 cracked their entire length.
I have previously had 3 others crack in similar fashion but I didn't keep track of their positions.
The plugs are AC Delco 41-983 plugs and I had put them in new when I was having similar issues which ended up being bad wires. I'm beginning to wonder if I got some factory defective ones since I've never seen plugs crack like this in my 45+ years of working on cars and airplanes.
Yep they were torqued correctly and nope I didn't drop them or put the socket on crooked.

I couldn't find any recent posts but some of the old ones showed using 41-932's which apparently have been discontinued and are now 41-993.
Any thoughts/recommendations are appreciated.
Different brand maybe??

[Arch Hoagland]

I'm curious where you bought them. For many years there has been a lot of counterfeiting going in many industries.

After reading of oil filters being counterfeited I decided to only buy my oil filters from Chevrolet dealers.

I've never heard of plugs cracking like that but I don't do that type of work so Ihaven't repalced but maybe 40 or 50 plugs over the years.

[Unplanned Tourist]

Can you post a couple of pics for us? Maybe someone will recognize the problem and come up with a cure, or at least an opinion, we have lots of those! Sounds like an odd failure.
Happy Glamping.

[bamaguy911]

Originally Posted by deputydog

My W22 had a rough idle and was missing under load again so I started with the "check the wires" (replaced them with a spare set I had and no difference) so I pulled the plugs and found the outside insulator of #7 and #8 cracked their entire length.

I assume the metal heat insulators are in use???

[guardrail53]

Originally Posted by deputydog

My W22 had a rough idle and was missing under load again so I started with the "check the wires" (replaced them with a spare set I had and no difference) so I pulled the plugs and found the outside insulator of #7 and #8 cracked their entire length.
I have previously had 3 others crack in similar fashion but I didn't keep track of their positions.
The plugs are AC Delco 41-983 plugs and I had put them in new when I was having similar issues which ended up being bad wires. I'm beginning to wonder if I got some factory defective ones since I've never seen plugs crack like this in my 45+ years of working on cars and airplanes.
Yep they were torqued correctly and nope I didn't drop them or put the socket on crooked.

I couldn't find any recent posts but some of the old ones showed using 41-932's which apparently have been discontinued and are now 41-993.
Any thoughts/recommendations are appreciated.
Different brand maybe??

I think you answered you own question? As this has happened before, a brand switch is in order!
FWIW, A.C. in AC Delco, stands for Albert Champion! I would go with the plug that he put his name on!
I never had good luck with the AC Delco brand of plugs in any of my gas engines! Always went with Champions! Rail!

[Unplanned Tourist]

Originally Posted by guardrail53

I think you answered you own question? As this has happened before, a brand switch is in order!
FWIW, A.C. in AC Delco, stands for Albert Champion! I would go with the plug that he put his name on!
I never had good luck with the AC Delco brand of plugs in any of my gas engines! Always went with Champions! Rail!

Yeah but AC Delco had such a cool jingle. 🎼🎵🎶🎵🎵 Anyone else remember that?
Happy Glamping.

[vettenuts]

Couple of thoughts. First, those plugs are still gapped at 0.060" and GM did have a bulletin out for reducing the gap to 0.045". Second, it is interesting that it's the rear two cylinders, which run a bit leaner. Think I would try cleaning the MAF and checking the air filter. Then I would personally replace with new plugs that come gapped at 0.045".

[LETMGROW]

Originally Posted by deputydog

My W22 had a rough idle and was missing under load again so I started with the "check the wires" (replaced them with a spare set I had and no difference) so I pulled the plugs and found the outside insulator of #7 and #8 cracked their entire length.
I have previously had 3 others crack in similar fashion but I didn't keep track of their positions.
The plugs are AC Delco 41-983 plugs and I had put them in new when I was having similar issues which ended up being bad wires. I'm beginning to wonder if I got some factory defective ones since I've never seen plugs crack like this in my 45+ years of working on cars and airplanes.
Yep they were torqued correctly and nope I didn't drop them or put the socket on crooked.

I couldn't find any recent posts but some of the old ones showed using 41-932's which apparently have been discontinued and are now 41-993.
Any thoughts/recommendations are appreciated.
Different brand maybe??

I have had no problems with AC Delco plugs. I use a lot of them in GM vehicles in my shop. It seems strange to me the plugs you had cracked were on opposite sides of the engine ( #7 & #8 ). Even if you had a cracked manifold causing heat on the porcelin portion of the plugs it shouldn't cause the plugs to crack. If the heat shields were not in place it would melt the wires before damaging the plugs.
Are you absolutely sure you had the plug wires firmly and completely pushed all the way onto the spark plug terminals? These can be difficult to get on the plugs with limited working space and the added friction of the shields. If the wires weren't all the way on to the plug terminal the gap left might and likely would cause heat which could damage the plug. I use a liberal amount of silicone Di-Electric lube on the inside and outside of the wire boot to aid in wire to plug installation. The amount you get with the plug wire set is simply not enough to satisfy me. I buy the lube by the tube.
I changed plugs and wires on my 8.1 this summer using AC 41-983 plugs gapped @ .060" and used Belden Edge premium wires. Even with the lube the wires were a bit of a challenge to get firmly into position.
When I installed the plugs I used a boot from the old wire set to hold the plug while screwing the plug into the cylinder head. I use a 3/8" bolt in the wire hole in the boot so I could reach into the head and clear the manifold with my fingers. My spark plug socket has a rubber insert inside it which helps keep the plug in the socket and keeps it aligned.
If you had a timing or fuel mixture problem it would show up on the electrodes and the porcelin around the electrode not at the outside of the plug.
Lynn

[deputydog]

I'll try to respond to the additional questions you posted - and thanks for the replys:
I'm pretty sure I bought the plugs from Autozone
The metal shields were installed (with the springs attached - I think Brazil cuts them off)
They were gapped at .060 per the manual - may try the .045 this time
The MAF is clean as is the air filter
The exhaust manifolds are not cracked
Dielectric compound was used but only a thin coat inside the boot
All my plug sockets have rubber boots inside them to protect the plugs
The internal insulator (plug tip) look good and the plug colorations appear normal (light tan) and no erosion of the plug tips
I posted photos of the three cracked plugs along with a couple of others with flaws beginning. I went through all the plugs I had (16) and 8 of them appeared fine but the other 8 were either cracked or had the beginnings of cracks/flaws. I'm beginning to wonder if I got a box that somebody dropped on the floor?? Until this time I unfortunately didn't keep track of which plugs were a set or which cylinder they came out of. The blue tape is where I numbered them this time.
Any ideas as to the differences between the 41-983, 41-932 and 41-993?
Thanks again for any thoughts/ideas/comments. I'm tired of crawling under this thing.

[Unplanned Tourist]

Are those definitely cracks, or carbon arc paths caused by arcing down the side of the plugs? May be the grease is causing this?
Happy Glamping.

[davebw31]

silicone Di-Electric grease does not conduct electricity. PERIOD Not using this type of grease or not applied liberally could promote carbon tracking. Besides it helps push the plug wire boot on a lot easier!

[Mudfrog]

Any ideas as to the differences between the 41-983, 41-932 and 41-993?

Probably wouldn't help with the cracking situation but i've seen several posters suggest going with Iridium 41-101 plugs gapped at .045.

[AKIQPilot]

Originally Posted by Mudfrog

Probably wouldn't help with the cracking situation but i've seen several posters suggest going with Iridium 41-101 plugs gapped at .045.

That is the only plug I will put in my 8.1's. And as you said, gapped at .045.

[deputydog]

Originally Posted by Unplanned

Are those definitely cracks, or carbon arc paths caused by arcing down the side of the plugs? May be the grease is causing this?
Happy Glamping.

Definitely cracks in the ceramic you can see under a strong loupe. The black in the cracks could be carbon but they are for sure cracked.