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Spark Plug Anomaly


Blue Bowtie
05-15-2022, 10:11 PM
I've seen my share of strange things over the years, but this one is a mystery. I pulled the two plugs from an off-road engine and found the side electrodes oddly bent. The two on the right are from the engine in question, and the one on the left is a "normal" plug from a running engine.

http://www.wwdsltd.com/files/1929DeereGPSparkPlugDamage.jpg

Closed observation reveals that the side electrodes seem to have been cut back, bent inward to the center electrode, and possibly filed at a slight angle.

The gap appears to be almost correct, at 0.025" (spec) but it certainly struck me a unusual.

Any speculation about why?

Stealthee
05-16-2022, 06:28 AM
It's called side gapping. There is a whole theory behind how it is supposed to put more of the spark in the fuel mixture.

maxwedge
05-16-2022, 08:30 AM
Yup, some racing plugs are made this way, to save money I did this myself in the pictured race car, supposed to be effective in wedge chambered heads.

Blue Bowtie
05-16-2022, 09:55 PM
Thanks Stealth (and Max). I don't recall encountering it exactly like that before, but I've only been doing this since about 1975.

Vanman1720
05-22-2022, 08:46 AM
That is interesting, I have been in the industry for a long time as well and I haven't even heard of this technique before...

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