A chain that skips — a lurch and a horrible clack under hard acceleration, like the drivetrain hiccupped — is one of the few chain symptoms that should genuinely stop your riding day. Skipping is the chain partially climbing out of the sprocket teeth; the next stage is coming off entirely, at whatever speed you happen to be doing. Here's the diagnosis, in order of likelihood.
Cause 1: Worn chain on worn sprockets
The dominant cause. A stretched chain's elongated pitch rides higher and higher on the sprocket teeth; the teeth, machined by that chain into hooks, eventually let it climb out under peak load. Check both in five minutes: the pull test and ruler measurement (how), and the tooth shapes (healthy vs hooked). If either fails, both are done — kit replacement, not adjustment.
Cause 2: Extreme slack
A wildly loose chain can whip and momentarily disengage under sudden load even with decent components — usually announced by heavy slap first (the sound guide). Measure and set to spec at the tightest point (the procedure), and ask why it got that loose — an axle walking forward or a chain at end-of-life (the loosening causes).
Cause 3: New chain, old sprockets
The false-economy special: fresh chain, original sprockets, and a skip under hard drive because correct pitch won't seat in re-machined teeth. The fix is the rear of the kit you skipped. This one's avoidable by policy: chains and sprockets are a set.
Cause 4: Bent guide or misalignment
Off-road bikes: a rock-bent chain guide feeds the chain onto the rear sprocket crooked, and crooked feed under load skips. Street bikes: severe wheel misalignment does the same more subtly. Sight down the chain run from the rear; the chain should feed dead straight onto the sprocket.
After the fix
Whatever the cause was, the follow-up is the same: correct slack, healthy components, and the inspection habit that catches stage one next time — skipping never arrives without pre-ride-visible warnings first. A clean chain makes every one of those warnings readable, which is one more job the one-minute brush habit quietly does.
Quick answers
What causes a motorcycle chain to skip?
A worn chain riding up hooked sprocket teeth is the classic cause — usually with excessive slack helping. A skipping chain is a derailment warning; diagnose before riding hard.
Can a new chain skip on old sprockets?
Yes — a new chain's correct pitch doesn't seat properly on sprockets machined by the old worn chain, and can jump under hard load. Chain and sprockets replace as a set.
Is chain skip dangerous?
Yes. Skipping means the chain is partially climbing out of engagement — the step before jumping the sprocket entirely, which can lock the rear wheel. Treat it as a stop-riding symptom.