2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 29Get this manual
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ENGINE SPECIFICATIONS Item Valve spring Free length IN EX Set length (valve closed) IN EX Compressed pressure (installed) IN EX Tilt limit IN EX Standard 37.03 mm (1.46 in) 37.68 mm (1.48 in) 27.87 mm