Evil engine noise

[Big hammer]

Car had been rough went and added fresh non corn gas.Was starting to run much better until, let off for a hill because going to fast for me, and when I put the gas pedal down, evil noise. Got back to garage removed timing cover, so far missing teeth on large gear. The noise came from the middle of the motor and sounded like someone using a hammer. I will pull pan and check out bearings.
FYI on engine noise and rough running engine