Diagnostic information and procedures

Refer to “engine symptom diagnosis” in section 1a .

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. 1
   Warm up the engine.
2. 2
   Lift and support the fuel tank. Refer to “fuel tank removal and installation” in section 1g (page 1g- 9).
3. 3
   Remove the air cleaner box. Refer to “air cleaner box removal and installation” .
4. 4
   Remove all the spark plugs. Refer to “ignition coil and spark plug removal and installation” in section 1h .
5. 5
   Install the compression gauge and adaptor in the spark plug hole. Make sure that the connection is tight.

Special tool
(a): 09915–64512 (compression
gauge)
(b): 09915–63311 (compression gauge
attachment)

6. Keep the throttle grip in the fully-opened position.

1. 1
   Press the starter button and crank the engine for a few seconds. Record the maximum gauge reading as the cylinder compression.
2. 2
   Repeat this procedure with the other cylinders.

• excessively worn cylinder walls
• worn piston or piston rings
• piston rings stuck in grooves
• poor valve seating
• ruptured or otherwise defective cylinder head gasket

• compression pressure in one of the cylinders is 1 000 kpa (10 kgf/cm2, 142 psi) and less.
• The difference in compression pressure between any two cylinders is 200 kpa (2 kgf/cm2, 28 psi) and more.
• All compression pressure readings are below 1 400 kpa (14 kgf/cm2, 199 psi) even when they measure 1 000 kpa (10 kgf/cm2, 142 psi) and more.

9. After checking the compression pressure, reinstall the removed parts.