Yamaha XMAX YP125R - Service manual > Checking the piston pin

1. Check:

• Piston pin

Blue discoloration/grooves → Replace the piston pin, and then check the lubrication system.

2. Measure:

• Piston pin outside diameter "a"

Out of specification → Replace the piston pin.

Piston pin outside diameter 13.995-14.000 mm (0.5510- 0.5512 in)

Limit 13.975 mm (0.5502 in)

3. Measure:

• Piston pin bore diameter "b"

Out of specification → Replace the piston.

Piston pin bore inside diameter 14.002-14.013 mm (0.5513- 0.5517 in)

Limit 14.043 mm (0.5529 in)

4. Calculate:

• Piston-pin-to-piston-pin-bore clearance Out of specification → Replace the piston pin and piston as a set.

Piston-pin-to-piston-pin-bore clearance =

Piston pin bore diameter "b" -

Piston pin outside diameter "a"

Piston-pin-to-piston-pin-bore clearance 0.002-0.018 mm (0.0001-0.0007 in)

Checking the timing chain guide

1. Check:

• Timing chain guide (exhaust side)

Damage/wear → Replace.

Installing the piston and cylinder

1. Install:

• Top ring "1"
• 2nd ring "2"
• Upper oil ring rail "3"
• Oil ring expander "4"
• Lower oil ring rail "5"

TIP

Be sure to install the piston rings so that the manufacturer marks or numbers face up.

2. Install:

• Piston "1"
• Piston pin "2"
• Piston pin clips "3"

TIP

• Apply engine oil to the piston pin.
• Make sure the punch mark "a" on the piston points towards the exhaust side of the cylinder.
• Before installing the piston pin clips, cover the crankcase opening with a clean rag to prevent the clips from falling into the crankcase.

3. Lubricate:

• Piston
• Piston rings
• Cylinder (with the recommended lubricant)

Recommended lubricant Engine oil

4. Offset:

• Piston ring end gaps

a. Top ring

b. Upper oil ring rail

c. Oil ring expander

d. Lower oil ring rail

e. 2nd ring

f. 20 mm (0.79 in)

A. Intake side

5. Install:

• Dowel pins
• Cylinder gasket
• Cylinder "1"

TIP

• While compressing the piston rings with one hand, install the cylinder with the other hand.
• Pass the timing chain and timing chain guide (intake side) through the timing chain cavity.

See also: