Yamaha YZ250FM 2021 Owner's Service Manual

ENGINE SPECIFICATIONS2-3Valve dimensionsValve seat contact width limit (intake) 1.6 mm (0.06 in)Valve seat contact width limit (exhaust) 1.6 mm (0.06 in)Valve stem diameter limit (intake) 4.945 mm (0.1947 in)Valve stem diameter limit (exhaust) 4.430 mm (0.1744 in)Valve guide inside diameter (intake) 5.000–5.012 mm (0.1969–0.1973 in)Valve guide inside diameter (exhaust) 4.500–4.512 mm (0.1772–0.1776 in)Valve-stem-to-valve-guide clearance limit(intake)0.080 mm (0.0032 in)Valve-stem-to-valve-guide clearance limit(exhaust)0.100 mm (0.0039 in)Valve stem runout 0.020 mm (0.0008 in)Valve springFree length limit (intake) 34.94 mm (1.38 in)Free length limit (exhaust) 33.82 mm (1.33 in)CylinderBore 77.000–77.010 mm (3.0315–3.0319 in)Wear limit 77.060 mm (3.0339 in)PistonPiston-to-cylinder clearance 0.030–0.055 mm (0.0012–0.0022 in)Diameter 76.955–76.970 mm (3.0297–3.0303 in)Measuring point (from piston skirt bottom) 4.0 mm (0.16 in)Piston pin bore inside diameter limit 16.043 mm (0.6316 in)Piston pin outside diameter limit 15.971 mm (0.6288 in)Piston-pin-to-piston-pin-bore clearance 0.002–0.022 mm (0.0001–0.0009 in)Piston ringTop ringEnd gap limit 0.50 mm (0.0197 in)Ring side clearance 0.030–0.065 mm (0.0012–0.0026 in)Side clearance limit 0.115 mm (0.0045 in)CrankshaftCrank assembly width 55.93–56.00 mm (2.202–2.205 in)Runout limit 0.030 mm (0.0012 in)ClutchClutch type Wet, multiple-discClutch lever free play 7.0–12.0 mm (0.28–0.47 in)Friction plate thickness 2.70–2.90 mm (0.106–0.114 in)Wear limit 2.60 mm (0.102 in)Plate quantity 8 pcsClutch plate thickness 1.50–1.70 mm (0.059–0.067 in)Plate quantity 7 pcsWarpage limit 0.10 mm (0.004 in)Clutch spring free length 46.20 mm (1.82 in)Clutch spring free length limit 43.89 mm (1.73 in)Push rod bending limit 0.30 mm (0.012 in)DrivetrainPrimary reduction ratio 3.353 (57/17)Transmission type Constant mesh 5-speed