2004 Yamaha YFZ450 Service and Repair Manual
The YFZ450 launches for 2004 as model code YFZ450S, and Yamaha's service manual for it is part number LIT-11616-17-11.
That book covers 2004 and 2005 together. Two model years is narrow coverage by Yamaha's standards, which suits a new sport machine: the tables stay short and the figures are unambiguous once you have matched your code.
The chapters work through periodic inspection and adjustment, engine and transmission service with measurement points, clearances, wear limits and tightening sequences, fuel and ignition specifications, electrical testing with the readings Yamaha expects, and chassis repair covering steering, suspension, wheels, brakes and the drive. Full wiring diagrams and troubleshooting charts are included.
On a machine built to be ridden hard, the factory service limits are what tell you whether a component is still within tolerance. Confirm YFZ450S on the frame and work from those numbers.