2004-2006 (2007) Honda TRX400FA Fourtrax Rancher / TRX400FGA Rancher AT GPScape Service Manual, Page 186Get this manual
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CYLINDERPISTON PISTONPISTON RING
Compare this measurement against the maximum cylinder I.Dmeasurement and calculate the cylinder-to-piston clearance (page 9-5)
Measure the piston pin hole