The specification—and exactly which bike it covers
For the 2020 U.S. Honda CRF250F, the owner’s manual specifies 30–40 mm (1 3/16–1 9/16 inches) of drive-chain slack. Check with the engine off, transmission in neutral and motorcycle on its side stand. Measure the lower run midway between the sprockets. Verify your own model-year manual before applying this number; a CRF250R, CRF300F or another motorcycle is a different application. [1]
Measure total up-and-down movement
The slack figure is the chain’s vertical travel at the specified point, not simply the gap between the chain and swingarm. Motion Pro’s tool instructions distinguish total slack from chain-to-swingarm measurements. Read the method before choosing a scale on a measuring tool. Take the measurement deliberately so you can reproduce it after any adjustment. [2]
Check more than one chain position
Honda calls for checking at several positions. With the engine stopped, carefully roll the motorcycle by hand to reposition the chain and repeat the check. Keep fingers clear of sprockets. Uneven readings, binding or damaged links deserve inspection; repeatedly changing an adjuster does not repair a damaged chain. See the drive-chain section beginning on printed page 98 of the linked manual. [1]
Before touching the adjusters
Record the readings first. If an adjustment is needed, follow the complete model-year procedure for axle loosening, wheel alignment, adjusters and final tightening. This article is a checking guide, so it does not substitute a generic torque number for the specified fasteners. Motion Pro also instructs users to recheck slack after the axle is tightened. A loose-axle reading is not the final check. [2]
Cleaning advice depends on the chain
Identify the fitted chain before choosing chemicals. D.I.D’s dedicated maintenance guidance calls for cleaner and lubricant compatible with sealed chains and warns against kerosene, gasoline, wire brushes and steam cleaning. If a general guide and the chain maker disagree, use the instructions for the actual chain rather than mixing procedures from different products. [3]
Keep a record you can use again
Write the manual edition, measuring position and readings in your service log. That turns the next check into a comparison instead of a fresh guess. Inspect before a ride rather than discovering a problem while loading the bike. If the readings vary sharply around the chain, have the chain and sprockets assessed together before treating the problem as routine adjustment.
Related reading: The CRF250F-to-CRF300F model transition.
Sources & technical information
- 2020 Honda CRF250F U.S. owner’s manual.
- Motion Pro: SlackSetter Pro instructions.
- D.I.D: drive-chain maintenance guidance.
Sources checked Oct 22, 2026 (UTC). Fitment, specifications and procedures vary; confirm the current manufacturer instructions for your exact bike and component.