8. CYLINDER HEAD/VALVES MXU 550EXi /MXU500i CYLINDER COMPRESSION TEST Warm up the engine to normal operating temperature. Stop the engine and remove the spark plug cap and remove the spark plug (refer to the "SPARK PLUG" section in the chapter 3). Park Plug Cap Compression Gauge Install a compression gauge into the spark plug hole. Open the throttle all the way and crank the engine with the starter motor until the gauge reading stops rising. The maximum reading is usually reached 4 7 seconds. To avoid discharging the battery, do not operate the starter motor for more than seven seconds. Compression pressure: 15 kg/cm2 (1500 kPa, 213 psi) Low compression can be caused by: Blown cylinder head gasket Improper valve adjustment Valve leakage Worn piston ring or cylinder High compression can be caused by: Carbon deposits in combustion chamber or on piston head 8-4