Yamaha XMAX YP125R - Service manual > Checking the cylinder and piston

1. Check:

• Piston wall
• Cylinder wall

Vertical scratches → Rebore or replace the cylinder, and replace the piston and piston rings as a set.

2. Measure:

• Piston-to-cylinder clearance

a. Measure cylinder bore "C" with the cylinder bore gauge.

TIP

Measure cylinder bore "C" by taking side-to-side and front-to-back measurements of the cylinder.

Then, find the average of the measurements.

Bore 52.000-52.010 mm (2.0472- 2.0476 in)

Taper limit 0.050 mm (0.0020 in)

Out of round limit 0.005 mm (0.0002 in)

b. If out of specification, rebore or replace the cylinder, and replace the piston and piston rings as a set.

c. Measure piston skirt diameter D "a" with the micrometer.

b. 5 mm (0.20 in) from the bottom edge of the piston

Piston

Diameter D 51.962-51.985 mm (2.0457- 2.0466 in)

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 "D"

Piston-to-cylinder clearance 0.015-0.048 mm (0.0006-0.0019 in)

Limit 0.15 mm (0.0059 in)

f. If out of specification, rebore or replace the cylinder, and replace the piston and piston rings as a set.

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 0.040-0.080 mm (0.0016- 0.0031 in)

Limit 0.120 mm (0.0047 in)

2nd ring

Ring side clearance 0.030-0.070 mm (0.0012- 0.0028 in)

Limit 0.120 mm (0.0047 in)

2. Install:

• Piston ring (into the cylinder)

TIP

Level the piston ring into the cylinder with the piston crown.

a. 10 mm (0.39 in)

3. Measure:

• Piston ring end gap

Out of specification → Replace the piston ring.

TIP

The oil ring expander spacer end gap cannot be measured. If the oil ring rail gap is excessive, replace all three piston rings.

Piston ring

Top ring

End gap (installed) 0.10-0.25 mm (0.0039-0.0098 in)

Limit 0.50 mm (0.0197 in)

2nd ring

End gap (installed) 0.10-0.25 mm (0.0039-0.0098 in)

Limit 0.60 mm (0.0236 in)

Oil ring

End gap (installed) 0.20-0.70 mm (0.0079-0.0276 in)

See also: