Curious Spark Plug Issue

[Thumperbird]

Has anyone seen this before?

The center electrode insulator on one of my plugs (Auotlite 3923) is broken away from the main insulator and just sort of hanging there sliding up and down around the electrode.

I can only assume the insulator was slid down and resting on the side electrode while running shrouding the spark.

Any possible causes engine wise?  Kinda weird.

[sixty9cobra]

I had the exact same problem ran like crap only when it was hot. MY neighbor said change the plugs. As I was doing thrm he was looking at them and was making fun of me how this plug was wasted. I ignored him because they only had a few thousand miles on them. After I finished I looked at the plugs and couldnt see any problem. he came back over and he couldnt find it either. Then we were tapping them and the center slid in and out creating no gap or a massive gap. They were autolite also.

[cjshaker]

I can't see anything in the engine that would cause this, short of blunt force trauma, which would have other serious signs showing somewhere. I'd chalk it up to a fluke, or some other quality issue (like maybe a 'bad' batch of ceramics or too thin in that particular area) with the plug maker. I've been using Autolite for 35+ years and never had that happen, but that doesn't mean it can't. 2 years ago, at the FE R&R, LarryK lost several ground straps on his racing Autolite plugs, which I had also never seen before. Now, depending on the motor, or how it's being used, I use a mix of Autolite or NGK, which I've always found to be excellent plugs (the NGK's). At work, I pretty much use NGK exclusively.

[Stangman]

Wow I’m a big fan of autolites and AC  Delco. I also haven’t seen this happen, but hey I don’t think anybody has the quality control like they had years ago. I dont know if it’s just me but a lot of things aren’t the same as they used to be. I use 3924 but I would have to imagine that doesn’t matter, makes me want to check my plugs. Now we have to check our plugs before we use them???!!!!

[Joe-JDC]

Over tightening can cause the body of the spark plug to separate from the ceramic and cause the problem you describe.  The torque value on most plugs is 15 lb/ft.  NKG has a warning about over-torqueing their plugs, and lists 22lb/ft as the maximum.  I found out the hard way on this when trying to index several sets of plugs with the crush washers.  Joe-JDC

[Stangman]

You got a point there Joe that is possible, you get a feel for this stuff when you change 1000s of plugs over the course of time. Even tightening and accidentally cocking it while doing your last snug. Like I said I have personally seen an old plug that was in my shop and I always had old timers give me there old parts and if you look we’re the porcelain and metal part the the socket goes on it doesn’t even look the same as the newer plugs. Hard for me to explain you would have to look at it yourself to see what I mean. Check it out someone has to have a set of plugs that have been sitting around for 20 -25 years and a new set.

[plovett]

I use Autolite 3924's and tighten the crush washers by hand.  I don't use a torque wrench.  I just feel it.  You can feel when the plug bottoms out on the washer, then you can feel it crush, then you can feel when it is crushed.  I am not saying that is the best way, but it has worked for me for decades.

JMO,

paulie

[Thumperbird]

I chose not to index but regardless I've done quite a few plug sets over the years, and since this was in aluminum heads I would like to think I was pretty cautious, i just go for a snug with 3/8 drive ratchet so not a ton of leverage.  Should have taken a picture, but for further detail, not chipped, cracked or anything else, just that whole tapered cylinder insulation section rattling around on the electrode.  3924's going back in "carefully" but do not recall doing anything stupid the first time around.

What's the consensus on the value of indexing on a 500hp 445 street motor?

 

[Joe-JDC]

Some plug mfgs. require anti-seize on their threads which can lead to overtightening, and especially if they have the crush washer.  That washer is designed to protect the plug housing from overtightening.  A torque wrench is the desirable way to install the plugs, but hand tightening is and has always been used by thousands successfully.  NGK does not require anti-seize on some of their plugs since they have a coating applied at the factory.  They do recommend using a torque value, and I did a test on old plugs to try to see where the body starts to separate from the ceramic.  It was like clockwork, at 22-25lb/ft, you could feel the plug stop moving, and the body turn just like stripping a set of threads on an aluminum part.  Joe-JDC

[Joe-JDC]

I chose not to index but regardless I've done quite a few plug sets over the years, and since this was in aluminum heads I would like to think I was pretty cautious, i just go for a snug with 3/8 drive ratchet so not a ton of leverage.  Should have taken a picture, but for further detail, not chipped, cracked or anything else, just that whole tapered cylinder insulation section rattling around on the electrode.  3924's going back in "carefully" but do not recall doing anything stupid the first time around.

What's the consensus on the value of indexing on a 500hp 445 street motor?

 

  I recently went through several sets of plugs on my EMC entry engine on the dyno, and we indexed the first set with the electrode facing/open to the exhaust valve, and made several pulls to establish a trend and repeatability.  Changed the plugs and indexed them to the intake valve, facing/open to the intake, and no difference after several pulls.  When we had over 50 or so dyno pulls, we changed the plugs again, and simply installed them without regard to indexing, and the power was still the same and repeated.  This was with aluminum heads, 55 cc chambers, and 13:1 compression, 565tq/595hp on 375 cubic inch Y Block.  We used NGK 10mm plugs, and found no gain or change in the horsepower by indexing the plugs using four sets during the testing to see if there was anything to be gained with indexing or fresh plugs.  Joe-JDC

[gdaddy01]

thank you for sharing that , I have often wondered if there was any gain to indexing . 

[70tp]

I had one do this once in a nitrous 302 in a ranger.    Would run ok off the bottle and miss on the bottle.  Pulled the plugs and #4 had the porcelain slid down over the gap. It was an autolite plug , big thread, taper seat. I just chalked it up to some detonation on pump gas as the cause    Only had it happen once.  Plug didn't show any signs of major distress other than the broken porcelain     No melted ground strap or center electrode probs

[cammerfe]

Forty plus years ago I was daily-driving an Austin Healey with a '3000' engine. I developed a miss that would come and go. I finally traced it to a plug with the porcelain cracked off so that the tip section would ride up and down on the center electrode. I found it while stopped on the side of the expressway---really annoyed at the on-'n'-off missing. I had a spare plug (with an Austin Healey you need to carry a variety of spares) and replaced the bad one. There was no sign of a reason and it never happened again. Go figure!!

KS

[Faron]

A Sad Heads Up , if the Metal Part of the Autolite Plug You Buy is shiny , its Made in China if its the dull Black , its Mexico