2013 Yamaha YZ250F — Owner's Manual
ADJUSTING THE DRIVE CHAIN SLACK. 1. Elevate the rear wheel by placing the suitable stand under the engine. 2. Check: Drive chain slack "a". Above the seal guard installation bolt.
Before checking and/or adjusting, rotate the rear wheel through several revolutions and check the slack several times to find the tightest point. Check and/or adjust the drive chain slack with the rear wheel in this "tight chain" position. Drive chain slack adjustment steps: a. Loosen the axle nut "1" and locknuts "2". b. Adjust the drive chain slack by turning the adjusters "3".
c. Turn each adjuster exactly the same amount to maintain correct axle alignment. (There are marks "a" on each side of the drive chain puller alignment.) NOTICE: Improper drive chain slack will overload the engine as well as other vital parts of the motorcycle and can lead to chain slippage or breakage. To prevent this from occurring, keep the drive chain slack within the specified limits.