Yamaha MTN850-A 2017, Service Manual, Page: 298 / 560

CONNECTING RODS AND PISTONS
5-63
TIP
Measure cylinder bore “C” by taking side-to-side
and front-to-back measurements of the cylinder.
b. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
c. Measure piston skirt diameter “P” with the mi-
crometer.
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.
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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 “a”, where cylinder wear is
lowest.
3. Measure:
•
Piston ring end gap
Bore
78.000–78.010 mm (3.0709–
3.0713 in)
Wear limit
78.060 mm (3.0732 in)
“C” = maximum of D
1
, D
2
, D
3
, D
4
, D
5
, D
6
Piston
Diameter
77.975–77.990 mm (3.0699–
3.0705 in)
a. 12.0 mm (0.47 in) from the bottom edge of
the piston
Piston-to-cylinder clearance = Cylinder bore “C” -
Piston skirt diameter “P”
Piston-to-cylinder clearance
0.010–0.035 mm (0.0004–0.0014
in)
Piston ring
Top ring
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Side clearance limit
0.115 mm (0.0045 in)
2nd ring
Ring side clearance
0.020–0.055 mm (0.0008–0.0022
in)
Side clearance limit
0.115 mm (0.0045 in)