A car jumps timing primarily due to a worn or failed timing component, most commonly the timing belt. This critical belt synchronizes the rotation of the engine's crankshaft and camshaft(s). When it stretches, slips, or breaks, the precise coordination between the pistons and valves is lost, which can lead to a no-start condition, poor performance, or catastrophic engine damage.
The root causes are almost always related to the timing system's components reaching the end of their service life or failing due to neglect.
- Worn Timing Belt: This is the number one culprit. Over time and miles, the rubber belt deteriorates, cracks, and stretches. A loose, stretched belt can jump teeth on the sprockets.
- Faulty Timing Belt Tensioner: The tensioner applies constant pressure to keep the belt tight. If it fails, the belt becomes slack and is highly likely to jump timing.
- Worn Timing Components: The guide pulleys that the belt runs against can wear out. Seized idler pulleys or a worn water pump (if it's driven by the timing belt) create excessive drag, which can also cause the belt to jump.
- Oil or Coolant Contamination: Leaks from valve covers or other engine seals can drip oil onto the timing belt. This oil degrades the rubber and can cause it to slip on the sprockets.
Ignoring the manufacturer's recommended replacement interval for the timing belt and its related components is the most common reason for this expensive problem. Interference engines are particularly vulnerable, as a jumped timing belt can cause the pistons to collide with the valves, resulting in severe internal damage.
