Spark Plug Problem

[jdotson]

What is considered a reliable spark plug for automotive engines? I have a friend who is running a new 383 with AC Delco plugs and one of the plugs lost an electrode yesterday. It didn't burn off, it looks like it either broke or came out of the porcelain a little ways up into the porcelain. The broke piece is now in the intake valve seat area and keeping the valve from closing properly. Is it common for a plug to do that or is it AC Delco quality? I'm planning on installing Autolites after pulling the head and fixing the valve issue.

 

[Olf Art]

JD, I'm answering only because our two engine gurus, Felber and Waterthunder aren't on here right now. They'll probably suggest you go to an NGK plug. They seem to be the best of the rest right now.

What happened to your buddy's engine was probably just a poor quality issue with the plug, but you might want to make sure that you check the plug length (reach) to make sure you're not installing a plug that's too long for that engine. Also, if the heads have been machined or the pistons changed, clearance might be too close at TDC.

 

[jdotson]

The center electrode is the only one missing, the ground electrode is fine and is not burnt or bent in any way. The center electrode did not break off flush with the porcelain but looks like it broke a little ways up into the porcelain. The porcelain is not damaged either, just a hole in the center where the electrode used to be.

 

[Olf Art]

Sorry, I missed that. OK, that sounds like just a defective plug. Thunder recommends an NGK B7ES for the Chevy small blocks.

 

[Waterthunder]

When ever possible I use NGK plugs and if their not available then I use a Autolite plugs their both great plugs and are the most commonly used ones in racing applications. I also recommend avoid using Champions when ever possible.

 

[jdotson]

Is this a freak incident or do some plugs fail like that from time to time?

 

[Croc1]

ac delco broke of the last 3 threads and ended up stuck in the rings of my dodge truck 2 years ago I had to trade it in quick

 

[Waterthunder]

These problems are not too common but they have the potential to be catastrophic. If you run N20, only the NGK and Autolite's hold up. On N20 it's even more critical to use a good quality plug.

 

[Anonymous]

Is this a freak incident or do some plugs fail like that from time to time?

Sorry I missed this post. Although I tend to agree w/Waterthunder, I also have to scratch my head.....I have seen several spark plugs missing the positive electrodes, but in all honesty, it has been when detonation was evident, and other parts of the spark plug beared witness. Now in my knowledge, I can't think of a single AC plug that doesn't have a ground electrode that covers the positive electrode, and the biggest gap I know of in OEM auto apps from the '80s was in the .080" range. So in order for a electrode that is at least that diametor to "fall out" from the gap, is basically impossible, unless the length of the electrode was under that dimension...

So if the ground electrode is fine with original gap(?????) It would have to be either a very short piece, or we have a very odd series of events.

Everyone reading, please bear w/forgive me while I'm thinking out loud.....I just can't see a sizable piece missing from the pos electrode while the rest of the plug is "perfect".......

All that comes to mind is.....Did you "side-gap" the plugs?....There was heat followed by cold (fuel wash) or a defective plug...But still after thousands of plugs under the most rediculous conditions...I can't see a perfect plug with a gap under .100 missing the POS electrode without melting.....

Something is missing here.....

 

[jdotson]

I'll try to get a pic of the plug later this week. Those are some good points Felber and a possibility. Maybe a pic will show more than I can describe.