Figure 4-1.GM mechanical governor.
control is effected by the action of the high-speed
(small) flyweights acting against a heavy (high-speed)
spring. See figure 4-2. If you have any questions or need
more illustrations to understand the concept of governor
operations, refer to chapter 9 of Engineman 3,
Mechanical governor faults are usually revealed in
speed variations. But not all speed variations are faults
of the governor. When abnormal speed variations
appear, you should first do the following procedures:
1. Check the load to be sure the speed changes are
not the result of load fluctuations.
2. If the load is steady, check the engine to make
sure all the cylinders are firing properly.
3. Make sure there is no binding in the governor
mechanism or operating linkage between the governor
and the engine. There should be no binding in the
injector control rack shaft or its mounting brackets. If
you find no binding anywhere and the governor still fails
Figure 4-2.Mechanical governor control mechanism.
to control the engine properly, you may assume that the
governor is worn or inoperative.
If the governor is the cause of improper speed
variations, it must be completely disassembled,
inspected, and rebuilt or replaced. When it is necessary
to disassemble and reassemble the governor, you should
secure a copy of the manufacturers instruction book and
follow the instructions given. During reassembly of the
governor, use only hard grease on the gasket! Under NO
circumstances should you use shellac on the gasket.
Adjustment procedures for the replacement of any
governor are listed in the manufacturers instruction
manual and should be followed with particular attention
given to the precautions listed.
OVERSPEED SAFETY DEVICES
Mechanical overspeed trips depend upon the
centrifugal forces developed by the engine and must be
maintained in good working condition. A faulty
overspeed device can endanger not only the engine but
also the personnel. The engine could explode or fly apart
because of the uncontrolled speed.
The engine instruction manual contains information
as to the speed at which the overspeed device is designed
to function. Most overspeed trips are adjustable. Before
making any changes in the adjustment of the overspeed
trip, you must determine the cause. If the engine did not
trip out, was it for some reason other than the action of
the element of the overspeed trip? You should first
check the accuracy of the tachometer and then test the