My belt keeps coming off or throwing
Belts and Tensioners
A belt that walks off a pulley is almost never a belt problem. It is an alignment problem, and it is worth finding the cause before you replace another belt.
Overview
Short Answer
If the belt is coming off, something is out of alignment. Lay a straightedge across the face of the crank and alternator pulleys. An offset that is invisible to the eye will show up immediately against a straightedge.
Work through these three checks in order
Check the alternator pulley for wobble with the engine running. A pulley that visibly moves side to side as it spins will push the belt off no matter how the rest of the system is set up.
Verify belt tension. About 1/4″ to 1/2″ of deflection at the longest span is typical on a serpentine setup.
Confirm every pulley sits in the same plane. A straight edge across the face of the alternator and crank pulleys will show any offset far better than eyeballing it.
If a pulley is out of plane, what puts it there
On a CVF bracket system, the water pump is the base that everything else references. The offsets we see most often come from:
- a water pump that differs from the one the kit was built around, which shifts the whole bracket
- a harmonic balancer with a different hub height than the one the kit expects
- spacers left out, doubled up, or installed in the wrong position
- a tensioner that is not seated flat on its bracket (see our article on tensioner seating)
What to send us
Belt alignment is hard to diagnose in text. Photos taken straight on rather than at an angle, showing the belt path, plus a shot with a straightedge laid across the pulley faces, tell us more than any description. Include your order number so we can pull the kit configuration you actually bought.
Safety
Do not keep running the engine with a belt that is walking off. A belt that comes off at speed can take a fan, a hose, or worse with it.
Still need help? Our tech support team can get you pointed in the right direction.
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