KYMCO MXU400 Service Manual page 47

Measuring Piston Skirt/
Cylinder Clearance
1. Measure the cylinder front to back in six places.
2. Measure the corresponding piston diameter at a
point 15 mm (0.6 in.) above the piston skirt at a
right angle to the piston-pin bore. Subtract this
measurement from the measurement in step 1. The
difference (clearance) must be within specifica-
tions.
Installing Piston Rings
1. Install ring expander (4) in the bottom groove of
the piston; then install the thin oil rings (3) over
the expander making sure the expander ends do
not overlap. Stagger the end gaps of the upper and
lower thin oil rings according to the illustration.
NOTE: Note the direction of the exhaust side of
the piston (5) for correct ring end gap orientation.
ATV-1069
2. Install the compression rings (1 and 2) so the let-
ter(s) on the top surface of each ring faces the
dome of the piston. Rotate the rings until the ring
end gaps are on directly opposite sides of the pis-
ton according to the illustration.
NOTE: The chrome (silver) ring should be
installed in the top position.
CC397D
Incorrect installation of the piston rings will result in
engine damage.
CYLINDER/CYLINDER HEAD
ASSEMBLY
NOTE: If the cylinder/cylinder head assembly
cannot be trued, they must be replaced.
Cleaning/Inspecting Cylinder Head
The cylinder head studs must be removed for this
procedure.
1. Using a non-metallic carbon removal tool, remove
any carbon buildup from the combustion chamber
being careful not to nick, scrape, or damage the
combustion chamber or the sealing surface.
2. Inspect the spark plug hole for any damaged
threads. Repair
"heli-coil" insert.
! CAUTION
! CAUTION
damaged threads using
ATV-1085B
3
MD1343A
a
3-17