When you over tighten a spark plug you can change the gap by one (or multiple of the following:

• Damage Ceramic/Porcelain Cap thus causing it to fall inwards which causes the electrode to touch the ground electrode.
• Distort the spark plug body which can cause the ground electrode to bend in some cases.
• Cause the ground electrode to touch a piston (if it is at TDC) some motors don't get close enough and some do.

There are some other ways you can close the gap on plugs, but those are usually the result of another catastrophic failure, so it doesn't really apply here.

I've also seen a bunch of people "tap" the ground electrode as they are inserting it, which effectively closes the gap... so that is also possible...

 

It's not always so easy NOT to accidentally tap the ground on the head. I've done that on all the plugs on my truck and my dads truck. Didn't do it on the 76 though, simply because the way the plugs were oriented.

 

Very true... I know I've done it... especially b/c of how the 5.7L Hemi's plugs are oriented.

 

I honestly don't think it affects it quite as badly as some might think.
I've pulled plugs out of my truck that have been "tapped" and their gap was fine. The big issue with letting the plugs "tap", imo, is the higher probability for dirt and crap to get stuck to the nose of the plug.

 

Yeah, you never know though... I've seen all kinds of fun stuff happen after people change their own spark plugs... always gives me a good laugh...

 

I normally tighten my plugs until I hear crack crack and all the porcelain shipping material falls off!


/s

 

Sorry, had to.

 

In over 45 years of dealing with spark plugs, I've never heard or seen this happen. The torque you would have to apply to the body of a plug would have to be astronomical, to change the gap, and if dealing with aluminum heads, you would strip the hole long before you would change the gap. As far as what Izero said about the ceramics falling in, I cant see how breaking the ceramics would ever change the gap. Yes, dropping the plug or beating an electrode could change it, but just a tap, I doubt it. Electrodes don't move very easily, and I like you have tapped them against the head before and actually checked them for movement, and have never found any, through just a casual bump

 

No disrespect but, please watch that video and tell me again what your 45 years of experience tells you... I've personally seen the electrode fall in and meet the ground electrode and you would never know it until you pulled it out... some people don't realize it until they try re-gapping the plug and realize that they can't gap it because the electrode keeps falling.

I've also personally seen each and every issue I mentioned...

 

No disrespect taken. I didn't say something couldn't happen, just that I had never seen or heard of it. Maybe it's because I never overtighten plugs, just snug them up and leave them. I cant imagine how tight you'd have to turn a plug to damage it like the one in the video. I was not saying that you were lying, just had never seen this before