Testing Engine Compression - KYMCO MXU400 Service Manual

2. Rotate the crankshaft to the TDC position on the
compression stroke.
NOTE: At this point, the rocker arms and adjuster
screws must not have pressure on them.
NOTE: Use Valve Clearance Adjuster for this pro-
cedure.
3. Place the valve adjuster onto the jam nut securing
the tappet adjuster screw; then rotate the valve
adjuster dial clockwise until the end is seated in
the tappet adjuster screw.
4. While holding the valve adjuster dial in place, use
the valve adjuster handle and loosen the jam nut;
then rotate the tappet adjuster screw clockwise
until friction is felt.
5. Align the valve adjuster handle with one of the
marks on the valve adjuster dial.
6. While holding the valve adjuster handle in place,
rotate the valve adjuster dial counterclockwise
until proper valve/tappet clearance is attained.
NOTE: Refer to the appropriate specifications in
Feeler Gauge Procedure sub-section for the proper
valve/tappet clearance.
NOTE: Rotating the valve adjuster dial counter-
clockwise will open the valve/tappet clearance by
0.05 mm (0.002 in.) per mark.
7. While holding the adjuster dial at the proper clear-
ance setting, tighten the jam nut securely with the
valve adjuster handle.
8. Place the two tappet covers with O-rings into posi-
tion; then tighten the covers securely.
9. Install the spark plug; then install the timing
inspection plug.
Testing Engine
Compression
To test engine compression, use the following proce-
dure.
1. Remove the high tension lead from the spark plug.
2. Using compressed air, blow any debris from
around the spark plug.
CF005
! WARNING
Always wear safety glasses when using compressed
air.
3. Remove the spark plug; then attach the high ten-
sion lead to the plug and ground the plug on the
cylinder head well away from the spark plug hole.
4. Attach the Compression Tester Kit.
NOTE: The engine must be warm and the battery
must be fully charged for this test.
5. While holding the throttle lever in the full-open
position, crank the engine over with the electric
starter until the gauge shows a peak reading of
95-115 psi (five to 10 compression strokes).
6. If compression is abnormally low, inspect the
following items.
A. Verify starter cranks engine over at normal
speed (approximately 400 RPM).
B. Gauge functioning properly.
C. Throttle lever in the full-open position.
D. Valve/tappet clearance correct.
E. Valve not bent or burned.
F. Valve seat not burned.
NOTE: To service valves, see Section 3.
7. Pour 29.5 ml (1 fl oz) of oil into the spark plug
hole, reattach the gauge, and retest compression.
8. If compression is now evident, service the piston
rings (see Section 3).
2
2-7