1-5
SECTION 1: GENERAL INFORMATION
If the RPM loss is greater than 75 RPM this indicates that the
grounded cylinder with the least RPM loss is the weakest of
the two cylinders. Look to that cylinder for a problem.
Example:
Engine RPM - Both Cylinders = 3400 RPM
Engine RPM - #1 Cylinder Grounded = 3300 RPM
Engine RPM - #2 Cylinder Grounded = 3100 RPM
Conclusion: #1 cylinder is weakest of the two cylinders.
Figure 1-8. Cylinder Balance Test
The cylinder balance test will also detect a cylinder that is not
functioning. When grounding out one cylinder there will be
no RPM loss. When the other cylinder is grounded out the
engine will stop.
CHECK FUEL:
The fuel pressure can be checked using a pressure tester kit
for LP and NG systems.
CHECK COMPRESSION:
It has been determined through testing that a simple and accu-
rate indication of compression can be made as follows:
Remove both spark plugs and insert a compression gauge into
either cylinder (one cylinder at a time). Turn engine over with
engine starter until there is no further increase in pressure.
Record this reading. Repeat procedure on other cylinder and
record that reading. The difference between both cylinders
should not exceed 25%. More than 25% indicates loss of com-
pression in the cylinder with lower pressure. See example.
EXAMPLE:
Cyl. #1 Cyl. #2 Diff.
Eng. #1 165 PSI 160 PSI 5 PSI
Eng. #2 175 PSI 155 PSI 20 PSI
If compression is poor, look for:
• Insufficient valve clearance
• Loose cylinder head bolts
• Blown head gasket
• Burned valves, valve seats and/or loose valve seats
• Warped cylinder head
• Warped valve stems
• Worn bore and/or rings
• Broken connecting rods
CYLINDER LEAKDOWN TEST
:
A cylinder leakdown tester may be used to test the sealing
capability of the compression components of each cylinder and
quickly identify the problem component.
THINGS WHICH AFFECT BOTH CYLINDERS:
1. Carburetion
2. Crankcase vacuum
3. Ignition timing
a. A partially sheared flywheel key will effect ignition timing
and engine performance.
THINGS WHICH AFFECT ONE CYLINDER:
1. Spark plug
a. A fouled spark plug may indicate that carburetor is out
of adjustment.
2. Leak in spark plug wire
3. Head gasket
4. Intake manifold
a. A leak at either end of the intake manifold will only affect
one cylinder, not both.
5. Valves
6. Rings
7. Piston
8. Cylinder
NOTE: A twin cylinder engine will run well on one cylin-
der as long as the power required for the application does
not exceed the power produced by the one cylinder.
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