Sudden development of loud knock in Cummins 8.3

I agree Carpediem 100% but these engines still need to be propped correctly even with the new heads.
I purchased a Searay a few years back that had one engine drop a valve 1.5 hours before purchase. I installed an EGT gauge on this Cummins repaired boat and found the temps to be over 1000 deg at cruise! After pitch reduction the temps dropped to under 750 deg. The certified Cummins mechanic also put the engine back together with the old, unchecked aftercooler which actually was so bad it needed to be replaced.
After the 12K the previous owner spent and the 5k I added to the mix it made a great boat.
 

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