Checking The Piston Rings - Yamaha MT-09 2021 Service Manual

c. Measure piston skirt diameter "b" with the
micrometer.
Piston
Diameter
77.975–77.990 mm (3.0699–
3.0705 in)
a
G089001
a. 9.0 mm (0.35 in) from the bottom edge of the
piston
d. If out of specification, replace the piston and
piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
Piston-to-cylinder clearance = Cylinder bore
"C" - Piston skirt diameter "b"
Piston-to-cylinder clearance
0.010–0.035 mm (0.0004–0.0014
in)
f. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
EAS30748

CHECKING THE PISTON RINGS

1. Measure:
• Piston ring side clearance
Out of specification → Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
Top ring
Side clearance limit
0.115 mm (0.0045 in)
2nd ring
Side clearance limit
0.115 mm (0.0045 in)
CONNECTING RODS AND PISTONS
b
G089002
2. Install:
• Piston ring
(into the cylinder)
TIP
Use the piston crown to level the piston ring near
bottom of cylinder, where cylinder wear is low-
est.
3. Measure:
• Piston ring end gap
Out of specification → Replace the piston
ring.
TIP
The oil ring expander spacer's end gap cannot
be measured. If the oil ring rail's gap is exces-
sive, replace all three piston rings.
Top ring
End gap limit
0.50 mm (0.0197 in)
2nd ring
End gap limit
1.15 mm (0.0453 in)
G089003
a. Bottom of cylinder
b. Upper of cylinder
5-71
a
b