What was found
THE NR 2 PROPELLER WAS REPLACED WITH AN O/H PROPELLER. GROUND RUNS REVEALED NO DISCREPANCIES AND THE ACFT WAS RETURNED TO SERVICE. THE ACFT FLEW A MISSION AND UPON RETURN THE CREW HAD A PROPELLER REVERSE THRUST WRITE-UP ON THE NR 2 PROPELLER. AFTER TROUBLESHOOTING, IT WAS DISCOVERED THAT A BETA ROD BLOCKING PIN WAS MISSING, UPON FURTHER INVESTIGATION, ALL 4 BETA RODS WERE FOUND TO BE SET AT DIFFERENT LENGTHS. PROPELLER WAS REMOVED AND RETURNED TO O/H FACILITY FOR REPAIR.