Honda CRF250F Owner's Manual Installation And Operation page 195

Adjustment:
If the drive chain requires adjustment, the
procedure is as follows:
1. Place a support block under the engine
to raise the rear wheel off the ground.
2. Loosen the rear axle nut (1) while
holding the rear axle shaft (2).
3. Turn both the right and left chain
adjusters (3) equally to increase or
decrease chain slack.
4. After adjusting, be sure the same
adjuster index marks (4) align with the
stopper pins (5) on both sides of the
swingarm.
If the drive chain slack is excessive when
the rear axle is moved to the furthest limit
of adjustment, the drive chain is worn and
must be replaced.
70
(3) (1)
(4)
(5)
(4)
(1) Rear axle nut
(2) Rear axle shaft
(3) Chain adjusters
(5)
(3)
(2)
(4) Index marks
(5) Stopper pins