Engine Mechanical (H4SO): Compression: Inspection

CAUTION: After warming-up, engine becomes very hot. Be careful not to burn yourself during measurement.

After warming-up the engine, turn the ignition switch to OFF.
Make sure that the battery is fully charged.
Release the fuel pressure. Refer to RELEASING OF FUEL PRESSURE , PROCEDURE, Fuel.
Remove all the spark plugs. Refer to REMOVAL , Spark Plug.
Fully open the throttle valve.
Check the starter motor for satisfactory performance and operation.
Secure the compression gauge tightly against the spark plug hole.
NOTE: When using a screw-in type compression gauge, the screw should be less than 18 mm (0.71 in) long.
Crank the engine by the starter motor, and read the maximum value on the gauge when the needle of gauge is steady.

Fig 1: Measuring Cylinder Compression
Courtesy of SUBARU OF AMERICA, INC.
Perform at least two measurements per cylinder, and check that the values are correct.
Compression (fully open throttle):

Standard 1,020 - 1,275 kPa (10.4 - 13.0 kgf/cm ² , 148 - 185 psi)

Difference between cylinders 49 kPa (0.5 kgf/cm ² , 7 psi) or less
After inspection, install the related parts in the reverse order of removal.