Yamaha YZF-R125 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.

Checking the piston pin


3. Measure:

  • Piston pin bore diameter "b" Out of specification Replace
    the piston.

Checking the piston pin


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"

    Checking the piston rings
    1. Measure: Piston ring side clearance Out of specification Replace the piston and piston rings as a set. NOTE: Before measuring the piston ring side clearance, eliminate any carbon deposits ...

    Installing the piston and cylinder
    1. Install: Top ring "1" 2nd ring "2" Oil ring expander "3" Lower oil ring rail "4" Upper oil ring rail "5" NOTE: Be sure to install the piston rings so that the manufacturer marks or ...

    Other materials:

    Ignition circuit cut-off system
    The ignition circuit cut-off system (comprising the sidestand switch, clutch switch and neutral switch) has the following functions. It prevents starting when the transmission is in gear and the sidestand is up, but the clutch lever is not pulled. It prevents starting when the t ...

    Installing the relay arm
    1. Lubricate: Spacers Bearings Oil seals Bolts (unthreaded shaft portion only) 2. Install: Bearing "1" (to the relay arm) Oil seal "2" (to the relay arm) 3. Rear shock absorber assembly 4. Relay arm 5. Connecting arm A. Left side B. Right side ...

    Intake air pressure sensor
    1. Check: Intake air pressure sensor output voltage Out of specification Replace the throttle body. a. Connect the pocket tester (DC 20 V) to the throttle body sensor assembly coupler as shown. Positive tester probe pink/white "1" Negative tester probe gray/black "2" ...

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