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Did a tune up on cub today, noticed when I took the plug boot off, the plug had a crack in the porcelain, or whatever it's called. What might cause it?
Poor material? I never go gorilla tightening them, just snug.

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Ya know not tightening spark plugs to spec, can cause the plugs to keep the heat & not transfer it to the head as fast.

Just sayin...

I don't think it was expansion & contraction. They are made to handle heat cycles.

I think the spec is either 18 or 22 ft lbs.

If you go to 15 ft lbs that would be safe.. Or wind them all the way in "by hand" then put the ratchet & socket on & give a good snug.