Yamaha YZ 2017 Series, Owner'S Service Manual

Page: 45 / 410

ENGINE SPECIFICATIONS
2-4
Valve spring
Free length (intake) 39.03 mm (1.54 in)
Limit 37.08 mm (1.46 in)
Free length (exhaust) 35.59 mm (1.40 in)
Limit 33.81 mm (1.33 in)
Installed length (intake) 32.50 mm (1.28 in)
Installed length (exhaust) 29.60 mm (1.17 in)
Spring rate K1 (intake) 25.56 N/mm (2.61 kgf/mm, 145.95 lbf/in)
Spring rate K2 (intake) 37.83 N/mm (3.86 kgf/mm, 216.01 lbf/in)
Spring rate K1 (exhaust) 24.53 N/mm (2.50 kgf/mm, 140.07 lbf/in)
Spring rate K2 (exhaust) 31.99 N/mm (3.26 kgf/mm, 182.66 lbf/in)
Installed compression spring force (intake) 155.00–179.00 N (15.81–18.25 kgf,
34.84–40.24 lbf)
Installed compression spring force (exhaust) 137.00–157.00 N (13.97–16.01 kgf,
30.80–35.29 lbf)
Spring tilt (intake) 1.7 mm (0.07 in)
Spring tilt (exhaust) 1.6 mm (0.06 in)
Winding direction (intake) Clockwise
Winding direction (exhaust) Clockwise
Cylinder
Bore 77.000–77.010 mm (3.0315–3.0319 in)
Taper limit 0.050 mm (0.0020 in)
Out of round limit 0.050 mm (0.0020 in)
Piston
Piston-to-cylinder clearance 0.030–0.055 mm (0.0012–0.0022 in)
Limit 0.15 mm (0.006 in)
Diameter 76.955–76.970 mm (3.0297–3.0303 in)
Measuring point (from piston skirt bottom) 4.0 mm (0.16 in)
Offset 0.00 mm (0.0000 in)
Piston pin bore inside diameter 16.002–16.013 mm (0.6300–0.6304 in)
Limit 16.043 mm (0.6316 in)
Piston pin outside diameter 15.991–16.000 mm (0.6296–0.6299 in)
Limit 15.971 mm (0.6288 in)
Piston ring
Top ring
Ring type Barrel
Dimensions (B

T) 0.90

2.70 mm (0.04

0.11 in)
End gap (installed) 0.15–0.25 mm (0.0059–0.0098 in)
Limit 0.50 mm (0.0197 in)
Ring side clearance 0.030–0.065 mm (0.0012–0.0026 in)
Limit 0.115 mm (0.0045 in)
Oil ring
Dimensions (B

T) 1.50

2.25 mm (0.06

0.89 in)
End gap (installed) 0.10–0.35 mm (0.0039–0.0138 in)