2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 299Get this manual
SWINGARM AND DRIVE CHAIN EBS00496
CHECKING THE DRIVE CHAIN 1Measure: 15-link section of the drive chain Out of specification Replace the drive chain15-link drive chain section limit (maximum) 240.5 mm (9.47 in) NOTE: While measuring the 15-link section, push down on the drive chain to increase its tension Measure the length between drive chain roller and as shown Perform this measurement at two or three different places2Check: drive chain Stiffness Clean and lubricate or replace3Clean: drive chain