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:

    Checking the crankshaft
    1. Measure: Crankshaft runout Out of specification Replace the crankshaft, bearing or both. NOTE: Turn the crankshaft slowly. 2. Measure: Big end side clearance Out of specification Replace the crankshaft. 3. Measure: Crankshaft width Out of specification&nbs ...

    Checking the spark plug cap
    1. Check: Spark plug cap resistance Out of specification Replace. a. Remove the spark plug cap from the spark plug lead. b. Connect the pocket tester ( × 1k) to the spark plug cap as shown. c. Measure the spark plug cap resistance. ...

    Checking and lubricating the cables
    The operation of all control cables and the condition of the cables should be checked before each ride, and the cables and cable ends should be lubricated if necessary. If a cable is damaged or does not move smoothly, have a Yamaha dealer check or replace it. WARNING! Damage to the out ...

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