Vent: Tried that 'just use a penny' trick to gap spark plugs on a Lycoming IO-360

I saw some forum hero swearing you could gap plugs with a penny in a pinch. Tried it on a run-up after an oil change at a little strip outside Amarillo. Cylinder 3 started shaking bad at 1800 RPM. Now I have to pull the plug and check for a bent electrode. Has anyone else had a backyard trick backfire like this?

2 comments

2 Comments

alice_palmer2025d ago

Wait, did you use a 1980s penny or a newer one? I read somewhere that modern pennies have a different thickness because they changed the metal blend in 1982. The old ones were mostly copper and a bit thicker. If you used a new one, you might have bent the electrode just from the gap being too wide. I heard a guy at my field say he tried it once on a Continental and had to replace two plugs after his engine started missing on climbout. That trick sounds way too sketchy for something like a Lycoming where the gap tolerance is super tight. Did you check the plug gap with a proper tool before you installed it?

kim_west24d ago

People get way too worked up about pennies and spark plugs. It's not like you're machining a part to a thousandth of an inch, just bending a little metal tab. Half the time the gaps are close enough anyway.