7. CYLINDER HEAD/VALVES MXU 250R/300R VALVE /VALVE GUIDE INSPECTION Inspect each valve for bending, burning, scratches or abnormal stem wear. If any defects are found, replace the valve with a new one. Check valve movement in the guide. Measure each valve stem O.D. Measure each valve guide I.D. Subtract each valve stem O.D. from the corresponding guide I.D. to obtain the stem- to-guide clearance. Service limits (replace if over): IN : 0.06 mm (0.0024 in) EX: 0.08 mm (0.0032 in) If the stem-to-guide clearance exceeds the service limits, replace the cylinder head is necessary. CYLINDER HEAD INPECTION Check the spark plug hole and valve areas for cracks. Check the cylinder head for warpage with a straight edge and feeler gauge. Service Limit: 0.05mm repair or replace if over. VALVE SPRING INSPECTION Measure the free length of the inner and outer valve springs. Service Limit (replace if below): Inner: 29.4 mm (1.176 in) Outer: 39 mm (1.56 in) 7-11