Service difficulty report · Screw · Cessna 421B

Difficulty date
December 25, 2014
Submitted
December 25, 2014
Operation
General aviation
Aircraft
N21WT
Make and model
Cessna 421B
Aircraft serial
0486
Aircraft time
4,298 hours
Engine
Cont GTSIO520C
Engine time
914 hours
Propeller
Mcauly 3AF34C92
Part
Screw
Part number
537750D
Condition
Sheared
Location
Intake Rocker
Stage of operation
CR
How discovered
O
Nature of condition
B, K, J
Precautionary procedure
E, J, A

As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.

What was found

RPM AND MANIFOLD PRESSURE STARTED FLUCTUATING FOR THE RT ENGINE. WHITE SMOKE FROM TURBO CHARGER VENTS WAS NOTED AS WELL AS OIL STREAKS NOTED. OIL PRESSURE DROPPED TO BOTTOM OF GREEN ARC ON THE OIL PRESSURE GAGE. EMERGENCY PROCEDURE CHECKLIST CALLED FOR ENGINE TO BE SHUTDOWN WITH THROTTLE CLOSED, PROP FEATHERED, MIXTURE IDLE CUT-OFF, FUEL VALVE TO BE CLOSED, MAGNETOS OFF, PROP SYNCHROPHASER OFF, AND ALTERNATOR OFF. ALSO ELECTRICAL LOAD WAS REDUCED. AFTER ENGINE INSPECTED ON THE GROUND IT WAS DETERMINED THAT THE 2 BOLTS ON THE ROCKER ARM HAD SHEARED AND THE PUSH ROD HAD MADE AN OPENING ON THE BOTTOM OF THE ROCKER COVER WHICH ALLOWED THE OIL TO FLOW OUT THE INTAKE SIDE OF THE NR 1 CYLINDER. THE PUSH ROD WAS NOT BENT. SUBSEQUENT CHECKING INDICATED NO METAL PARTICLES IN THE OIL OR OIL FILTER.

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