A healthy chain makes a soft whirr. A dry chain squeaks or grinds, a loose chain slaps against the slider and swingarm on bumps, and a worn chain or sprocket clatters as the rollers ride up the teeth. Noise is the chain's early warning: most causes are cheap to fix if you catch them before the chain and sprockets wear out.
Is it safe to ride?
Ride with care and check it today. A noisy chain can be close to jumping off or snapping, which can lock the rear wheel.
Quick checks first
- Engine off, bike on the stand: look at the chain. Dry, orange, or shiny?
- Push the chain up and down at the middle of the lower run. Very loose or very tight?
- Look for marks where the chain hits the swingarm, slider or guard.
- Look at the rear sprocket teeth.
- Check wheel alignment. The front and rear sprockets must be in line, or the chain wears more on one side. Look along the chain to see that it runs straight.
Diagnose it step by step
1Is the chain dry, rusty or dirty?
- Yes: Clean and lubricate the chain. If the noise goes, that was it.
- No: go to step 2.
2Is the slack outside the specified range? (K-Light 125: 20 to 40 mm, bike upright.)
- Yes: Check and adjust chain slack.
- No: go to step 3.
3Does the slack change a lot as you roll the bike forward (tight in places, loose in others)?
- Yes: Chain is tight in some places and slack in others.
- No: go to step 4.
4Are the sprocket teeth hooked, sharp or broken, or can you lift the chain away from the back of the rear sprocket?
- Yes: Inspect sprockets and Check the chain for wear. Worn parts are replaced as a set.
- No: go to step 5.
5Are there rub marks on the slider, swingarm, guard or chain case?
- Yes: Chain rubs on the guard, slider or swingarm.
- No: go to step 6.
6Is the noise a clunk when you open or close the throttle?
- Yes: Clunk or snatch from the rear wheel.
- No: go to step 7.
7Still noisy with a good chain and sprockets?
- Spin the rear wheel by hand: a rumble points to the bearings (Check wheel bearings). A whine that changes with gear points to the gearbox (Whining noise in one or more gears). Check the front sprocket is tight on its shaft.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Dry or dirty chain | Looks dry or rusty, squeaks | Clean and lubricate the chain |
| Wrong slack | Measured outside range | Check and adjust chain slack |
| Worn chain or sprockets | Hooked teeth, chain lifts off sprocket | Check the chain for wear |
| Rubbing on slider or guard | Shiny or cut marks | Check chain guides, sliders and guards |
| Worn cush drive | Clunk on throttle changes | Check the cush drive rubbers |
| Wheel bearing | Rumble when wheel spun | Check wheel bearings |
Reference values (K-Light 125)
| Item | Value | Source |
|---|---|---|
| Chain slack, lower run, bike upright | 20 to 40 mm | K-Light 125 manual, PDF p. 61 |