Checking Compression Pressure

1. Before checking engine compression, check the engine oil level. Also check that the starter motor and battery are all in normal operating condition.
2. Start the engine and wait until the engine coolant temperature reaches 80 ~ 95°C (176 ~ 205°F).
3. Turn off the engine and disconnect the spark plug cables.
4. Remove the spark plugs.
5. Crank the engine to remove any foreign material in the cylinders.
6. Insert the compression gauge into the spark plug hole.
7. Depress the accelerator pedal to open the throttle fully.
8. Crank the engine and read the gauge.

   Standard value : 1200 kpa (12.2 kg / cm² , 170 psi)

   Fig 1: Reading Compression Gauge

   Courtesy of HYUNDAI MOTOR CO.
9. Repeat steps 6 to 8 for all cylinders, ensuring that the pressure difference for each of the cylinders is within the specified limit.

   Limit 

   Max. 100 kpa (1.0 kg / cm² , 14 psi) between cylinder

10. If a cylinder's compression or pressure differential is outside the specification, add a small amount of oil through the spark plug hole, and repeat steps 6 to 9.
    1. If the addition of oil causes the compression to rise, it is likely that there may be wear between the piston ring and cylinder wall.
    2. If compression remains the same, valve seizure, poor valve seating or a compression leak from the cylinder head gasket are all possible causes.

Tightening torque 

Spark plug : 20 ~ 30 Nm (200 ~ 300 kg.cm, 14 ~ 22 lb.ft)