What was found
(CAN) A/C EXPERIENCED ENG OIL PRESS PROBLEM. TROUBLESHOT & CONSULTED WITH O/H SHOP, UNABLE TO RECTIFY OIL PRESSURE PROBLEM. ENGINE REMOVED/OVERHAULED & INSTALLED. ENG HAD OVER MAX OIL PRESSURE (100 PSI) AT HIGHER RPM SETTING, AT IDLE, OIL PRESSURE WOULD DROP BELOW NORMAL OPERATING RANGE AIRCRAFT WAS GROUNDED. AFFECTED ENGINES SENT TO ANOTHER OVERHAUL FACILITY FOR ANALYSIS AND REPAIR.ENGINE DISASSEMBLED, DISCOVERED 12 IMPROPER VALVE LIFTERS 646277 HAD BEEN INSTALLED. O/H SHOP CONFIRMED THIS WOULD CAUSE POOR OIL PRESSURE. ENGINE REPAIRED AND TESTED AFTER RE-ASSEMBLY, OIL PRESSURE READINGS WERE EXCELLENT.