Note: During the inspection, the engine must be at normal operating temperature, oil level and battery fully charged.
1. Before removing the spark plugs, clean the area around them.
2. Remove the spark plugs from the engine.
3. Disconnect the coil wire from the center socket of the distributor cap and ground it to the engine housing.
4. Install the compression gauge into the #1 spark plug hole. Press the gas pedal to the floor to open the throttle valve. Rotate the engine shaft through at least 4 compression strokes, observing the gauge. In a normal engine, compression increases quickly. Low compression in the 1st stroke with an increase in subsequent strokes indicates worn piston rings. If the compression is low in the 1st stroke and does not increase in subsequent strokes, this indicates leaks in the valves or a ruptured head gasket (another cause may be a cracked cylinder head). Record the maximum reading of the gauge.
5. Repeat the procedure for the remaining cylinders and compare the obtained data with those given in the specification and table (see figure). The difference between the highest and lowest readings should not exceed the values specified in the table.
6. Add a little engine oil into each cylinder through the spark plug hole, then repeat the test.
7. If the compression increases after adding oil, the piston rings are definitely worn. If there is no significant increase in compression, then leaks are occurring through the valves or the cylinder head gasket. Valve leaks can be caused by burnt valve seats, as well as by skewed, cracked or bent valves themselves.
8. If two adjacent valves have equally low compression, then there is a high probability of a ruptured cylinder head gasket between them. This is confirmed by the appearance of coolant in the combustion chambers or in the oil.
9. If the compression is higher than normal, then the combustion chambers may be covered with carbon deposits. In this case, the cylinder head must be removed and cleaned.
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