Why does my PU timing belt drift or mistrack, and how do I fix it?

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Short answer: PU timing belts usually drift or mistrack because of pulley misalignment (shafts not parallel or not square to the belt path), incorrect or unstable tension, worn or damaged pulley teeth and flanges, debris in the drive, or a poorly made weld on an endless joined belt. Fix it in that order: check alignment first, then tension, then pulley condition, then cleanliness — and only then suspect the belt itself.The four usual suspectsShaft alignmentNon-parallel shafts or a squareness error between pulley and belt path push the belt to one flange. A straightedge, laser line or even a taut wire reveals most cases quickly.TensionToo little tension lets the belt climb and skip; too much overloads cords and bearings and can also worsen edge wear. Verify against the manufacturer tension table for the profile and width.Pulley conditionWorn tooth flanks, damaged flanges, or a missing crown on flat back-side idlers all encourage running off center. Inspect pulleys whenever a new belt shows drift.Debris and wear productsPacking dust, cord particles and swarf accumulate in tooth gaps and on guides, lifting the belt line off center. Cleaning is the cheapest fix in the list.Most drift cases trace back to alignment or tension rather than the belt itself.Symptom to cause quick tableSymptomLikely causeFirst actionBelt rides hard against one flange, noisy edgeShaft misalignment or pulley not squareCheck parallelism with straightedge or laserDrift appears after tension changeTension too low or unevenRe-measure tension to the profile tableDrift started with a new belt on an old driveWorn pulley teeth or flange damageInspect and replace worn pulleysIntermittent wander along the pathDebris, worn guides, bad splice squarenessClean the drive and inspect the weld lineEdge wear on one side onlyPersistent misalignmentCorrect alignment, then re-check after run-inDiagnosis checklistLock out the machine and check shaft parallelism across the full belt span, not only at one pulley.Measure tension with a proper gauge and compare with the recommended value for your profile and width.Run the belt slowly by hand and watch where it first touches a flange — that point points to the offending component.On welded endless PU belts, check that the weld line is square to the belt edges; a skewed splice visibly walks the belt.After correcting, run in briefly and re-verify: alignment corrections often need one small follow-up trim.Alignment errors are the leading cause of belt drift and edge wear. Tension values and minimum pulley diameters differ by profile, cord type and manufacturer. Persistent drift after alignment, tension and cleanliness are correct may indicate a splice or manufacturing issue — in that case, stop adjusting and have the belt inspected to avoid masking a real defect.Stable tracking needs correct alignment, tension and clean guides working together.Drift that will not go away?Send photos of the drive, your profile and width, tension readings and the tracking behavior — our engineers will help you isolate the cause and propose the right belt or tension setup.Get Tracking Help

Why does my PU timing belt drift or mistrack, and how do I fix it?

The four usual suspects

Shaft alignment

Tension

Pulley condition

Debris and wear products

Symptom to cause quick table

Diagnosis checklist

Drift that will not go away?

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Symptom	Likely cause	First action
Belt rides hard against one flange, noisy edge	Shaft misalignment or pulley not square	Check parallelism with straightedge or laser
Drift appears after tension change	Tension too low or uneven	Re-measure tension to the profile table
Drift started with a new belt on an old drive	Worn pulley teeth or flange damage	Inspect and replace worn pulleys
Intermittent wander along the path	Debris, worn guides, bad splice squareness	Clean the drive and inspect the weld line
Edge wear on one side only	Persistent misalignment	Correct alignment, then re-check after run-in