Yamaha MT-09 2021 - Checking the Piston Rings

5-71
CONNECTING RODS AND PISTONS
c. Measure piston skirt diameter “b” with the
micrometer.
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.
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.
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.
Piston
Diameter
77.975–77.990 mm (3.0699–
3.0705 in)
a. 9.0 mm (0.35 in) from the bottom edge of the
piston
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)
Top ring
Side clearance limit
0.115 mm (0.0045 in)
2nd ring
Side clearance limit
0.115 mm (0.0045 in)
a
b
G089001
Top ring
End gap limit
0.50 mm (0.0197 in)
2nd ring
End gap limit
1.15 mm (0.0453 in)
a. Bottom of cylinder
b. Upper of cylinder
G089002
a
b
G089003