Compression Test Conclusion - Ford LSG 875 Service Manual

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BASIC ENGINE
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DIAGNOSIS AND TESTING (Continued)
TEST CONCLUSION
The indicated compression pressures are con-
sidered normal if the lowest reading cylinder is
within 75% of the highest. Refer to the following
example.
Seventy-five percent of 140, the highest cylin-
der reading, is 105. Therefore, cylinder No. 7
being less than 75% of cylinder No. 3 indicates
an improperly seated valve or worn or broken
piston rings.
3. If two adjacent cylinders indicate low com-
pression pressures and squirting oil on the
pistons does not increase the compression,
the cause may be a cylinder head gasket
leak between the cylinders. Engine oil and/
or coolant in the cylinder could result from
this problem.
It is recommended that the following quick ref-
erence chart be used when checking cylinder
compression pressures. The chart has been cal-
culated so that the lowest reading number is
-
If one or more cylinders read low, squirt ap-
proximately one (I) tablespoon of engine oil on
top of the pistons in the low reading cylinders.
Repeat compression pressure check on these
cylinders.
1. If compression improves considerably, the
piston rings are at fault.
75% of the highest reading.
EXAMPLE
After checking the compression pressures in
all cylinders, it was found that the highest read-
ing obtained was 196 psi. The lowest pressure
reading was 155 psi. The engine is within speci-
2. If compression does not improve, valves are
fications and the compression is considered
sticking or seating poorly. satisfactory.
Maximum Minimum Maximum Minimum Maximum Minimum
PSI PSI
PSI
PSI PSI
PSI
134 101
174 131 214 160
136 102 176 132
216 162
138 104 178 133 218 163
140 105 180 135 220 165
142 107 182 136 222 166
144
108 184
138 224 168
146 110 186
140 226 169
148 111 188
141
228
171
150 113 190 142 230
172
152 114 192 144 232
174
154
115
194
145 234 175
156 117 196
147
236
177
158 118 198 148 238 178
160 120 200 150 240 180
162
121 202 151 242 181
164
123 204 153 244 183
166 124 206
154 246 184
168 126 208 156 248
186
170 127 210 157 250
187
172
129
212 158
CA1005A
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