Did you know? The valve clearance on your Yamaha YZ or WR should be checked every 3 races or 500 km of use. After 5 races or 1,000 km of use the piston rings should be replaced and the top end should be inspected. Not Properly maintaining a modern four-stroke can create an extremely expensive repair bill. Riding your Yamaha is more fun than spending a bucket load of money fixing something you could have prevented with a little time and the right information.The Cyclepedia.com Yamaha YZ and WR 400, 426, and 450 digital motorcycle service manual features detailed full-color photographs and wiring diagrams, complete specifications with step-by-step procedures performed and written by a veteran Yamaha dealer trained motorcycle technician.The Yamaha YZ WR 400, 426, 450F digital motorcycle manual covers the following off-road and motocross motorcycles:1998 Yamaha YZ400FK1998 Yamaha WR400FK1999 Yamaha YZ400FL1999 Yamaha WR400FL2000 Yamaha YZ426FM2000 Yamaha WR400FM2001 Yamaha YZ426FN2001 Yamaha WR426FN2002 Yamaha YZ426FP2002 Yamaha WR426FP2003 Yamaha YZ450FR2003 Yamaha WR450FR2004 Yamaha YZ450FS2004 Yamaha WR450FS2005 Yamaha YZ450FT2005 Yamaha WR450FT