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engine oil before engine startup. The oil fill plug on all
3161 Governors is located on the top cover.
Gerotor Oil Pump
The gerotor oil pump is located in the base of the
governor. The inner rotor of the pump is driven by a pin
in the drive shaft, and carries the outer rotor around in
mesh, this pushes oil to the accumulator piston.
The 3161 Governor is a mechanical-hydraulic
A single accumulator, that consists of a piston
governor that senses (feels) engine speed and is
and spring, acts as a relief valve for the oil pump and
connected to the engine fuel system by mechanical
supplies a reservoir of high pressure oil for rapid power
linkage. The governor controls the rate of fuel injected
piston movement. Oil is sent to the accumulator by the
into each of the engine cylinders as needed to adjust for
governor pump, with an increase in pressure as the
engine loads.
accumulator spring is put under compression. When the
pressure gets to a set point, oil is returned to sump
Droop and compensation can be adjusted on the
through relief ports in the piston wall.
governor as needed for stability of engines with different
rates of engine speed changes.
Power Piston
The 3161 Governor has a maximum of 8 Nm (6
lb. ft.) of torque output over the full 42 degrees of
The power piston is fastened to the output shaft
terminal (output) shaft rotation in both the fuel ON and
by a link and lever assembly. The power piston has a
OFF directions. Because the governor terminal shafts
large area on the bottom and a small area on top
are moved in both directions by hydraulic pressure, no
(differential piston). A small pressure increase on the
return spring is used on the outside of the governor. A
large area of the piston will move the piston up, this
1.4 Nm (1 lb. ft.) spring inside the governor moves the
causes the output shaft to turn in the "increase" direction.
terminal shafts to the full shutoff position when the
The piston can move down only when oil under the
governor is not in operation.
piston is released to sump. Oil to or from the bottom of
the power piston is controlled by the ballhead pilot valve
The recommended travel (rotation) of the
and ballhead pilot valve bushing.
terminal shafts is approximately 30 degrees from low idle
to full load. This gives extra travel at each end for the
governor to make a complete shutdown and gives
Pilot Valve System
maximum fuel when needed.
The pilot valve system  is  made  of  two
The 3161 Governor is connected to the engine
components, the ballhead pilot valve (rotating) bushing,
lubrication oil system. The oil supply (under pressure) is
and the ballhead pilot valve plunger.  The bushing is
sent to the governor through an orifice and internal
turned relative to the pilot valve plunger to reduce friction
passages. The governor keeps the correct oil level and
between the two parts. The control land of the pilot valve
drains excess oil back into the engine, this gives a
plunger controls the flow of oil through the control ports
constant flow of oil through the governor.
of the ballhead bushing.
After removal or overhaul, the governor must be
filled with approximately 1.8 liters (2. U.S. qt.) of clean


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