Yamaha YFM660RN Service Manual

Contents

5 - 35ENGCYLINDER AND PISTONCHECKING THE PISTON RING1.Measure: Ring side clearanceUse a feeler gauge.Out of specification → Replace the pistonand rings as a set.NOTE:Clean carbon from the piston ring grooves andrings before measuring the side clearance.Side clearanceStandard LimitTopring0.04 ~ 0.08 mm(0.0016 ~ 0.0031 in)0.13 mm(0.0051 in)2ndring0.03 ~ 0.07 mm(0.0012 ~ 0.0028 in)0.13 mm(0.0051 in)2.Position: Piston ring(in cylinder)NOTE:Insert a ring into the cylinder and push itapproximately 50 mm (2.0 in) into the cylinder.Push the ring with the piston crown so that thering will be at a right angle to the cylinder bore.a 50 mm (2.0 in)3.Measure: Ring end gapOut of specification → Replace.NOTE:You cannot measure the end gap on theexpander spacer of the oil control ring. If the oilcontrol ring rails show excessive gap, replaceall three rings.End gapStandard LimitTopring0.30 ~ 0.45 mm(0.0118 ~ 0.0177 in)0.70 mm(0.0276 in)2ndring0.30 ~ 0.45 mm(0.0118 ~ 0.0177 in)0.80 mm(0.0315 in)Oilring0.2 ~ 0.7 mm(0.0079 ~ 0.0276 in) —