6G- 66 1973 OPEL SERVICE MANUAL
6. Check compression of each cylinder. Repeat
compression check and record highest reading ob-
tained on each cylinder during the two pressure
checks.
The recorded compression pressures are to be con-
sidered normal if the lowest reading cylinder is more
than 75 percent of the highest reading cylinder. See
the following example and the “Compression Pres-
sure Limit Chart.” See Figure
6G-2.
Seventy-five percent of 140 (highest) is 105. Thus,
cylinder No. 4 is less than 75 percent of No. 3. This
condition, accompanied by low speed missing, indi-
cates an improperly seated valve or worn or broken
piston ring. See Figure 6G-1.
2
3
I
SO-1
Figure 6G-1 Example of Compression Check
7. If one or more cylinders read low, inject about a
tablespoon of engine oil on top of pistons in low
reading cylinders through spark plug port. Repeat
compression check on these cylinders.
a:
If compression improves considerably, rings are
lV0*tl.
b. If compression does not improve, valves are stick-
ing or seating poorly.
c. If two adjacent cylinders indicate low compression
and injecting oil does not increase compression, the
cause may be the head gasket leaking between the
cylinders. Engine coolant and/or oil in cylinders
could result from this defect.
Compression Pressure Limit Chart
This chart may be used when checking cylinder com-
pression pressures. It has been calculated so that the
lowest reading number is 75 percent of the highest
reading number. See Figure 6G-2.
EXAMPLE:
After checking the compression pressures
in all cylinders, it was found that the highest pressure
obtained was 182 psi The lowest pressure reading
was
145psi.
By locating 182 in the maximum col-
umn, it is seen that the minimum allowable pressure
r
-.__
MAXIMUM
PRESSURE
POIJNW
W.
INCH
--
134
136
138
140
142
146
148
150
152
154
156
158
160
lb2
164
166
168
170
172
174
176
178
180
182
184
186
MINIMUM
PRESSURE
POUNDS/
SQ. INCH
HAXIMUM
‘RESSURE
‘OUNW
iQ. INCH
MINIMUM
PRESSURE
“OUNW
X?.
INCH
101 188
I41
I02
190
142
104 192 144
105 194 145
107 196 147
II0
198 148
Ill 200 150
113
202
151
114
204
153
115
206
154
117
208
156
118
210
157
120
212
158
121
214
160
123
216
162
124
218
163
126
220
165
127
222
166
129
224
168
131
226
169
132
228
171
133
230
172
135
232
174
136
234
175
138 236
177
140 238
178
Figire
6G.2 Compression Pressure Limit Chart
is 136psi. Since the lowest reading obtained was 145
psi, the car is within limits and the compression is
considered satisfactory.
Spark Plugs
1. Inspect, clean and regap or replace spark plugs as
required. Correct gap is
,030.
2. Install spark plugs. Tighten to 30 lb.ft.
Secondary Ignition System
1. Inspect ignition cables for broken, swollen or
deteriorated insulation.
2. Check terminal ends and condition of rubber
boots. Replace as required.
3. Inspect the condition of the distributor cap and
rotor.
4. Clean the ignition coil and inspect for cracks or
carbon paths which could cause high voltage leak-
age.
Distributor Contact Points
1. Inspect distributor contact points and replace or
adjust as necessary
(.016
gap).
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