[Ed Snyder]

Originally Posted by massey478

I-6 engines were bad about inhaling a carb air cleaner mount retaining screw on the carb top that vibrated loose or other trash that might get unnoticed into the air cleaner when changing it. Instant knock! I have seen the screws pressed into the piston top virtually permanently. Head off, new piston, hopefully no cracked head or scored cylinder.

I know from painful experience exactly what Marti is talking about here. The original 305D in my '62 Suburban somehow inhaled the threaded rod holding the air cleaner lid down. Instant loud knocking followed by loss of power and big clouds of oil smoke out the exhaust. Head removal revealed the smashed threaded rod and a piston broken in half. That incident led to the installation of the 401M.