Compression Readings; Example Readings; Cylinder Leakage Detector; Oil Leak And Valve Guide Seal Test - Ford LRG-423 Service Manual

01-8
Engine Service 01-8
SERVICE PROCEDURES (Continued)
Compression Readings - Interpreting
It is recommended the Compression Pressure Limit
Chart be used when checking cylinder compression so
that the lowest reading number is 75 percent of the
highest reading.
If one or more cylinders reads low, squirt
approximately one tablespoon of SAE 50 weight, or
equivalent, engine oil on top of the pistons in the low
reading cylinders. Repeat compression pressure
check on these cylinders.
1. If compression improves considerably, piston
rings are at fault.
2. If compression does not improve, valves are
sticking or seating poorly.
3. If two adjacent cylinders indicate low
compression pressures and squirting oil on
pistons does not increase compression, cause
may be a cylinder head gasket leak between
cylinders. Engine oil and/or coolant in cylinders
could result from this problem.
Example Readings
If, after checking the compression pressures in all
cylinders, it was found that the highest reading
obtained was 1351 kPa (196 psi) and the lowest
pressure reading was 1069 kPa (155 psi), the engine
is within specification and the compression is
considered satisfactory.
Cylinder Leakage Detector
When a cylinder produces a low reading, the use of
Rotunda Pressurization Kit 014-00705, or equivalent,
will be helpful in pinpointing the exact cause.
The leakage detector is inserted in the spark plug
hole, the piston is brought up to top dead center on the
compression stroke, and compressed air is admitted.
Once the combustion chamber is pressurized, a
special gauge will read the percentage of leakage.
Leakage exceeding 20 percent is considered
excessive.
While the air pressure is retained in the cylinder, listen
for the hiss of escaping air. A leak by the intake valve
(6507) will be audible in the carburetor. A leak by the
exhaust valve (6505) can be heard at the exhaust
pipe. Leakage past the rings will be audible at the
positive crankcase ventilation (PCV) connection. If air
is passing through a blown gasket to an adjacent
cylinder, the noise will be evident at the spark plug
hole of the cylinder into which the air is leaking. Cracks
in the cylinder block (6010), or gasket leakage into the
cooling system may be detected by a stream of
bubbles in the radiator (8005).
ROTUNDA
PRESSURIZATION
KIT
014-00705
A23452-A
-
Oil Leak and Valve
Guide Seal Test
The cylinder leakage detector can be used to test for
engine oil leaks and to check the valve seals for
leakage.
1. Plug all crankcase openings except the one used
for connecting the leakage detector.
2. Connect the detector to a crankcase opening.
The oil level indicator tube (6754) is convenient.
Adjust the air pressure to approximately 34 kPa
(5 psi).
3. Using a solution of liquid soap and water, brush
the solution along the gasket sealing surfaces
and bearing seals. Look for bubbles or foam.
4.
Remove the spark plugs (12405) and rotate the
engine slowly with a wrench. Check for large
amounts of air escaping into the cylinders as
each intake and exhaust valve opens.
The spark plugs (12405) on the leaking cylinders
will probably show deposits of burned oil.
Intake Manifold Vacuum Test
Bring the engine to normal operating temperature.
Connect Rotunda Vacuum/Pressure Tester
059-00008, or equivalent, to the intake manifold. Run
the engine at the specified idle speed.
The vacuum gauge should read between -51 and
-74 kPa (15 and 22 in-Hg) depending upon the engine
condition and the altitude at which the test is
performed. SUBTRACT 5.5 kPa FROM THE
SPECIFIED READING FOR EVERY 500 METERS
(1 in-Hg for every 1,000 feet) OF ELEVATION ABOVE
SEA LEVEL.