by the scavenge oil system. The following subparagraphs discuss the pressure and scavenge oil systems.
The pressure oil system supplies oil at 85 to 95 psi to the reduction gearbox where it is
divided into two branches. One branch is led to the first stage reduction gears, splines, torquemeter, and
number 3 and 4 bearings. Pressure oil to the torquemeter is led through a metering valve which controls
the flow into the torquemeter chamber. The bearings and gears are lubricated by oil spray jets. The
second branch supplies oil to the propeller governor unit, the accessory drive gears, and propeller thrust
The scavenge oil system includes two double-element scavenge pumps connected by
internal passages and lines to two main external transfer tubes. One pump is secured inside the
accessory gearbox and the other is externally mounted. They are contained in separate housings and
driven off accessory gearshafts.
The oil from the No. 1 bearing compartment is returned by gravity through an internal
cored passage to the bottom of the compressor inlet case and then through internal passages in the oil
tank and accessory diaphragm into the accessory gearbox. Number 2 bearing oil drains down from its
compartment into an external sump leading rearward to the bottom of the tank. It is then scavenged to
the scavenge pump which forces the oil into the accessory gearbox. The oil from the centrifugal
breather and the input gearshaft and bearings drains to the bottom of the accessory gearbox. It is then
scavenged from the gearbox together with the oil from No. 1 and 2 bearings by the rear element of the
double-element internal scavenge pump. The internal scavenge pump is driven by a quillshaft from the
main oil pump in the oil tank. The external scavenge pump scavenges any reduction gearbox oil which
drains rearward when the engine is in extreme climbing attitudes. Oil from the propeller governor, front
thrust bearing, reduction gear, and torquemeter bleed orifice drains into the reduction gearbox sump.
The oil is then scavenged by the external scavenge pump through the external transfer tube to the
accessory gearbox housing. The oil from both internal and external scavenge pumps is forced through a
T fitting into the airframe oil cooler, where the oil is cooled and passed on to the oil tank. The normal
oil operating temperature is 74 to 80 C.
The torquemeter is a hydromechanical torque-measuring device located inside the first stage
reduction gear housing. The