My Dad had a similar experience, only it was he who dropped a machine screw down the carb of his 440. Not a big one, maybe half an inch long. Instead of pulling the carb and fishing it out, he ran the motor thinking the screw would blow out the exhaust. It didn't. I don't remember how we determined it was still in the motor or what side it was in, but I pulled one head and there it was, lightly embedded in a piston. Thank goodness he didn't run it long. Pulled out the screw, leaving an impression of a screw head and threads in the (stock cast) piston. Put it back together and drove it for several years like that.
He wasn't so lucky when he dropped an exhaust valve in his Hemi then drove it for five miles to get home. That did some real damage. (Hint: not a good idea to run 87 octane gas in a 12.5 to one Hemi.)
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