Broken Spark Plug

[Demetri]

What do you think caused it?

[Demetri]

[Superman]

If you show a pic of the broken end, some of the many engineers here could offer educated guesses. Me? Manufacturing defect is my guess.

[manbridge 74]

What’s with the marks on the screw on tip? Looks like it’s been overtightened or suffered some trauma causing part to fail further down....

[smadsen]

Threads corroded. Plug wrench on cock-eyed/not properly engaged. Then max torque. Usually some combination of the above.

[DerkPerk]

Neve seen one snapped like that with the ceramic still intact.


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[Major Dad]

I’ve had four out of six go like that when I removed them from my 2.4S recently, same brand and make as OP.

[manbridge 74]

Counterfeit comes to mind….

[Flat Six]

Center electrode broken, looks like axial failure (twisting load, not side load). Since the electrode's broken but not the ceramic insulator (and based on the marks on the aluminum ferrule), I'd guess someone overtightened the screw-on ferrule w/pliers. BTW, a 9-range plug is really cold . . . .

[Demetri]

Maybe it was an over tightened ferrule? I tightened them by hand. They always seem to be loose out of the box. They are in my 83 SC ROW. The cold plug helps with detonation.

[Dave Kost]

Maybe the plug was dropped before it was installed.

[rgrimm]

First time I changed plugs on my '68 I had that happen. No cracks or break in the ceramic at all, just the center electrode (and about in the same place)

[Demetri]

Thank you for all the input! I’ll keep you posted. I tightened the ferrule on the replacement plug, too.��

[manbridge 74]

I tighten the ferrule with smooth jaw pliers. Leaves no mark and they are tighter than hand tight but not too tight (because clamping/turning pressure is low).