Engine Engine Mechanical
Diagnostic Information and Procedures
Engine Mechanical Symptom Diagnosis
Refer to “Engine Symptom Diagnosis in Section 1A (Page 1A-7)”.
Compression Pressure Check
The compression pressure reading of a cylinder is a good indicator of its internal condition. The decision to overhaul the cylinder is often based on the results of a compression test. Periodic maintenance records kept at your dealership should include compression readings for each maintenance service.
• Before checking the engine for compression pressure, make sure that the cylinder head nuts are tightened to the specified torque values and the valves are properly adjusted.
• Make sure that the battery is in fullycharged condition.
1) Warm up the engine.
2) Remove the fuel tank lower cover. Refer to “Fuel Tank Removal and Installation in Section 1G (Page 1G-9)”.
3) Remove the spark plug. Refer to “Spark Plug Cap and Spark Plug Removal and Installation in Section 1H (Page 1H-4)”.
4) Install the compression gauge and adaptor in the spark plug hole. Make sure that the connection is tight.
(A): 09915–64512 (Compression gauge)
(B): 09915–63311 (Compression gauge attachment)
5) Disconnect the fuel pump lead wire coupler (1).
6) Remove the ignition switch and connect the ignition switch coupler. Refer to “Ignition Switch Removal and Installation in Section 1H (Page 1H-7)”.
7) Shift the transmission to the neutral, turn the ignition switch ON and grasp the clutch lever.
8) Keep the throttle lever in the fully-opened position.
9) Press the starter button and crank the engine for a few seconds. Record the maximum gauge reading as the cylinder compression. Compression pressure specification Low compression pressure can indicate any of the following conditions:
• Excessively worn cylinder wall
• Worn piston or piston rings
• Piston rings stuck in grooves
• Poor valve seating
• Ruptured or otherwise defective cylinder head gasket
10) After checking the compression pressure, reinstall the removed parts.
Engine Components Removable with the Engine in Place. Engine components which can be removed while the engine is installed on the frame are as follows. For the installing and removing procedures, refer to respective paragraphs describing each component.