Diagnose this truck

Can you diagnose this motor? ...What be broke in the motor?

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I'd bet valve contact since they had it adjusted recently. Knock sounds pretty fast.

 

Agreed. Something in the valve train is bent (push rod, rocker arm, valve bridge or valve) causing excess clearance, and why the noise. If something was broken there would be no noise, just a miss.

 

Melted piston, broken ring(s), scored cylinder. I would assume that at the very least so you are not surprised. A compression check would be a good idea.