Generac Power Systems GP Series Diagnostic Repair Manual page 46

Section 5 Engine Diagnostic Tests
Remove both spark plugs.
3.
Remove air cleaner cover and air filter
4.
Use a finger to manually open throttle plate to wide
5.
open position.
Disconnect Wire 16 from starter contactor (SC).
6.
Connect one lead from the remote push button
7.
starter to Wire 16 terminal on the SC.
Figure 1-74. Remote Push Button Starter Connected
Connect the other lead from the remote push
8.
button starter to the positive battery terminal.
Insert a compression gauge into one cylinder.
9.
Crank the engine until there is no further increase
10.
in pressure.
Record the highest reading obtained.
11.
Repeat the procedure for the remaining cylinder
12.
and record the highest reading.
NOTE: See Specifications
values.
When done with testing:
13.
a. Re-install air cleaner cover and air filter.
b. Reconnect Wire 16 to SC.
c. Re-install fuses.
d. Re-install spark plugs.
e. Return unit to normal operation.
Results
The difference in pressure between the two cylinders
should not exceed 25 percent. If the difference in
compression is greater that 25 percent, loss of
compression in the lowest reading cylinder is indicated.
Example 1: If the pressure reading of Cylinder #1 is 165
PSI and of Cylinder #2 is 160 PSI the difference is 5 PSI.
Divide "5" by the highest reading (165) to obtain the
percentage of 3.0 percent.
Cylinder Leak Down Test
The Cylinder Leak Down Tester checks the sealing
(compression) ability of the engine by measuring air
leakage from the combustion chamber. Compression
loss can present many different symptoms. This test is
designed to detect the section of the engine where the
40
015250
for acceptable compression
fault lies before disassembling the engine.
represents a standard tester available on the market.
NOTE: Refer to the tool manufacturer's instructions for
variations of this procedure.
A
C
B
0
0
F
H
G
0
A. Compressed air in
B. Air pressure regulator
C. Inlet gauge pressure set point
D. Outlet gauge pressure
E. To spark plug hole
F. Regulator adjustment knob
G. Outlet gauge
H. Red range indicates unacceptable leakage
I. Needle indicates minimal air leakage
J. Green range indicates acceptable leakage
Figure 5-75. Cylinder Leakdown Tester
Procedure
Remove F1 and F2 fuses.
1.
Remove the spark plug(s) from the cylinder.
2.
Gain access to the flywheel or to the generator fan
3.
assembly. Remove the valve cover.
Rotate the engine crankshaft until the piston reaches
4.
top dead center (TDC) of the compression stroke on
the cylinder being tested. In this position, both the
intake and exhaust valves will be closed. If the
engine is not properly positioned at TDC the results
of the test may be inaccurate.
Attach cylinder leak down tester adapter to spark
5.
plug hole.
Connect an air source per the tool manufacturer's
6.
requirements to the cylinder leak down tester.
NOTE: Refer to the tool manufacturer's instructions for
proper setting.
Monitor the flywheel/generator fan for rotation from
7.
top dead center as you apply air in the next step.
Adjust the regulated pressure on the gauge to the
8.
manufactures setting for the tool that you are using—
typically 90 psi. Verify flywheel/fan has not rotated.
Read the gauge on the tester for cylinder percent
9.
of leakage. A leakage of 20 percent is normally
acceptable. Use good judgment, and listen for air
escaping at the carburetor (air intake), the exhaust,
the side of the head where head and block join,
Figure 5-75
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Diagnostic Repair Manual
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