33
ST SERIES
ENGINE PARTS CHECK
❱❘ Piston
• In case of fitting an used piston, check the following points:
• Skirt: Looking for seizure marks. Lights marks can be removed with
a soft stone.
• Ring grooves: rings must be free in their grooves. In order to clean
the grooves, you can use an old ring.
• The ring pins should not be worn or loose.
• Rings : check condition and end gap
❱❘ End gap
• Insert the ring in the cylinder, using the piston to make it square to the cylinder axis, to
about 10mm of the cylinder deck.
• Measure end gap using a thickness gauge.
Ring end gap :
Standard :
125 : 0.35mm – 0.50mm
250 / 300 : 0.2mm – 0.4mm
❱❘ Wrist pin check
Wrist pin diameter ; 125cc:
Standard : 14,998 mm
Wear limit : 14,995 mm
Wrist pin hole ; 125cc
Standard : 15,003mm
Wear limit : 15,007mm
Wrist pin diameter ; 250/300cc
Standard : 17,998 mm
Wear limit : 17,995mm
Wrist pin hole ; 250/300cc
Standard : 18.002 mm
Wear limit : 18.006 mm
If the end gap is greater than specified, you must check cylinder and piston condition. If
they are within tolerance, only replace the rings.
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