What was found
(CAN) AFTER T/O, SMOKE ACCUMULATED IN THE CABIN. THE FWD AND AFT SMOKE DETECTORS LOCATED IN THE LAVS ACTIVATED. SUCCESSFULLY RETURNED TO AIRPORT. MX CARRIED OUT ENG GROUND RUNS & COULD NOT DUPLICATE DEFECT ON GROUND. A TEST FLT ORDERED & AND IN FLT SMOKE PRESENTED IT SELF AGAIN. THROUGH T/S IN AIR IT DETERMINED THAT BY TURNING OFF THE A/C PACK ON 1 SIDE THAT SMOKE STOPPED ACCUMULATING. ACRFT RETURNED TO AIRPORT FOR FURTHER TROUBLESHOOTING. MX FOUND OIL IN AIR CON COALESOR BAG WITH AFFECTED A/C PACK INOP. ACFT FLOWN TO A NEARBY AIRPORT FOR FURTHER MX. AN INTERNAL OIL LEAK FOUND IN ENG 654717 AROUND THE C1 AND C2 BEARING. THIS OIL MADE ITS WAY TO THE BLEED AIR SYSTEM AND INTO A/C PACK.