Incident Description
Oil was observed leaking from the propeller shaft seal assembly. An investigation revealed that the seal components had not been assembled in the correct sequence. Specifically, the half flat spacer was positioned forward of the seal rather than aft. This misplacement compressed the seal and forced it against the seal runner. The resulting friction from the rotating seal runner caused abnormal wear, enabling engine oil to escape.
Assembly Process
During assembly, the engineer consulted the Illustrated Parts Catalog (IPC) diagram rather than the Engine Maintenance Manual (EMM) diagram, which depicted the correct order of parts. Although the engineer referred to the EMM, he did not notice that its assembly procedure and diagram differed from those in the IPC. Additionally, the engineer relied on his memory of the order in which the parts were removed. The investigation noted that this recall may have been affected by fatigue associated with longer working hours and disrupted sleep.
Findings
The oil leak originated from the incorrect assembly order of the propeller shaft seal components. The error occurred because the engineer followed the IPC diagram instead of the EMM diagram and depended on memory, which may have been impaired by fatigue from extended work hours and irregular sleep.