What was found
(CAN) FLIGHT CREW NOTED AN ENGINE OIL BYPASS PIN POPPED ON PREFLIGHT. REMOVED OIL FILTER FOR INSPECTION AND FOUND PEICES OF THE OIL FILTER ALUMINUM CASE TRAPPED IN THE FILTER. THE END OF THE FILTER THAT CONTAINS THE O-RING HAD BROKEN AND PIECES WERE DRAWN INTO THE FILTER. THIS CAUSED THE OIL-BYPASS PIN TO POP WHEN THE RESTRICTION BECAME HIGH ENOUGH. INSTALLATION WAS FOUND TO BE CORRECT. ALL PEICES OF THE FILTER WERE ACCOUNTED FOR. OIL WAS DRAINED, SOAP SAMPLES TAKEN AND NO FURTHER CONTAMINATION OF THE SYSTEM WAS NOTED.