Checking The Piston Rings - Yamaha MTN850-A 2017 Service Manual

TIP
Measure cylinder bore "C" by taking side-to-side
and front-to-back measurements of the cylinder.
Bore
78.000–78.010 mm (3.0709–
3.0713 in)
Wear limit
78.060 mm (3.0732 in)
"C" = maximum of D , D
1
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.
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
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 "P"
, D , D , D , D
2 3 4 5 6
CONNECTING RODS AND PISTONS
Piston-to-cylinder clearance
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.
Piston ring
Top ring
Ring side clearance
Side clearance limit
2nd ring
Ring side clearance
Side clearance limit
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
5-63
0.010–0.035 mm (0.0004–0.0014
in)
0.030–0.065 mm (0.0012–0.0026
in)
0.115 mm (0.0045 in)
0.020–0.055 mm (0.0008–0.0022
in)
0.115 mm (0.0045 in)