Page 28 - Nov21T

Four months of non-flying produced a Santa-like beard.
vibration, no oil-starved prop dome gears, and no cranking against dry metal on the next start-up. Enter Lycoming Service Instruction 1462A.
My Kingdom for Oil Pressure
According to Lycoming, SI 1462A should be accomplished “Whenever sluggish propeller action is reported, when the engine does not hold RPM during cruise, climb or descent, or whenever the engine (I’m certain they meant propeller) is going into feather during landing roll out with reduced throttle setting.” The purpose of the air pressure check to the propeller governor system is to determine if the governor oil passages have excessive clearance, leaks or blockages (tight clearance). The air pressure check shows the condition of governor oil passages, front bearing clearance, and positioning of the governor circuit oil plug. The test procedure directs you to attach a test plate and pressure gauge to where the prop governor mounts to the engine. First, the test plate is used to verify oil psi with the engine running – this verifies you have good baseline oil psi. Next, you shut down the motor, attach a differential air pressure tester to the same test plate and input 40 PSI.
The output (prop governor circuit) should be between 6 and 35 PSI. The Duke’s was around five. The reason for the low number was that during the engine overhaul, while within tolerance, the crankshaft was undersize. The overhauler installed new “normal” sized bearings on the
26 • TWIN & TURBINE / November 2021
Turbines