Checking engine compression
1. A compression test will show you what condition the engine is in. Low compression indicates leaks caused by worn piston rings, defective valves and their seats, or a burnt head gasket.
2. Warm up the engine to normal operating temperature, shut it off and wait 10 minutes to allow the catalytic converter temperature to drop. On models without a catalytic converter, there is no need to wait 10 minutes.
3. First, clean the area around the spark plugs so that dirt does not get into the cylinders when checking the compression. Remove the spark plugs.
4. Disconnect the primary wire from the distributor. Lock the throttle and choke so they are open.
5. With a pressure gauge inserted into the #1 cylinder spark plug hole, crank the engine through at least four compression strokes and observe the pressure gauge reading. Compression should build up quickly. Low compression on the first stroke that does not increase on subsequent strokes indicates worn valves, a blown head gasket, or a cracked head. Record the highest pressure gauge reading and compare it with the data given in Specifications.
6. Repeat the procedure on the remaining cylinders. The lowest compression value should not be less than 70% of the highest. No reading should be less than 7.9 bar.
7. Pour in a couple of teaspoons of engine oil (best with a syringe) into each cylinder through the spark plug hole and repeat the test.
8. If after that the compression increased noticeably, the piston rings are worn out. If the compression has not increased, there is a leak in the valves or through the cylinder head gasket. Leaking valves can be caused by burnt seats or deformed and cracked valves.
9. If two adjacent cylinders have the same low compression, the cylinder head gasket is most likely burned between them. The presence of coolant in the combustion chambers or crankcase confirms this version.
10. If the compression is higher than normal, the walls of the combustion chambers are probably covered with soot. Remove the cylinder head and remove carbon deposits.
11. If the compression is below normal or its differences between the cylinders are large, contact a specialist for a special leak test.