Chain Failure Glossary
Failure mode
Chordal Action
Also known as Polygon effect, cyclic speed variation
What chordal action is
Because a chain seats on a sprocket as a polygon rather than a circle, the effective radius changes through each engagement. Chain speed and tension rise and fall with every tooth, adding cyclic load, vibration and impact at entry. The effect intensifies with fewer teeth.
Common causes
- Sprockets with a low tooth count, especially below 17 teeth
- High chain speed where the speed ripple becomes significant
- Long centres without a tensioner to absorb the ripple in slack side tension
- Loose chain allowing the polygon effect to amplify into snatch
Warning signs
- Regular vibration or speed pulsation at each tooth engagement
- Heavy impact marks at sprocket entry and roller wear
- Chain surge on the slack side even at steady load
- Noise that increases with speed rather than with load
Prevention and correction
- Increase sprocket tooth count, keeping the largest practical driver
- Fit a tensioner or idler to control slack side movement
- Use a chain with a smaller pitch for the same load
- Reduce speed where the drive ratio allows
Fix it with the right product
Chain and sprocket specificationNeed a second opinion?
Send us the chain, the running hours and a photo. Our engineers will confirm the failure mode and quote the right replacement.
All chain failure modes
Chain ElongationFatigue FailureSide Plate CrackingPin and Bush WearRoller Wear and SpallingAbrasive WearAdhesive WearCorrosionStress Corrosion CrackingHydrogen EmbrittlementGallingSurface PittingTensile OverloadShock LoadingImpact FractureLubrication StarvationTight Links and KinkingMisalignmentChordal ActionSprocket Tooth Wear
Same & Next-Day Delivery Areas
Roller chain supply across South Yorkshire & the North
Dispatched from our Rotherham depot — order by 1pm for next-working-day delivery, or collect same-day within our 30-mile radius.
RotherhamDepot location
Sheffield9 mi · ~25 min
Barnsley6 mi · ~15 min
Doncaster16 mi · ~30 min
Mexborough3 mi · ~8 min
Maltby5 mi · ~12 min
Wath-upon-Dearne4 mi · ~10 min
Wakefield20 mi · ~35 min
Leeds25 mi · ~45 min
Huddersfield30 mi · ~50 min
Scunthorpe22 mi · ~35 min
Mansfield28 mi · ~45 min
Chesterfield18 mi · ~30 min
Worksop14 mi · ~25 min