* Worn or damaged timing gears: The teeth on the camshaft and crankshaft gears can wear down, particularly if the engine has high mileage or has been poorly maintained. This wear can lead to slippage and ultimately a jump. Stripped teeth are a more dramatic failure mode.
* Broken or stretched timing chain: While less common than gear problems on this engine, a worn or broken timing chain can cause the gears to jump. A chain is more flexible than gears and therefore can skip a link or two if there's sufficient slack or a component failure.
* Loose or worn timing gear sprockets: The sprockets are the parts that the gears bolt onto. If these are loose or worn, it can allow for misalignment and slipping.
* Excessive slack in the timing chain tensioner (if equipped): A failing tensioner won't maintain sufficient tension on the chain, leading to slack and potential jumps.
* Severe engine damage: Internal engine damage (like a connecting rod failure) can cause such violent movement that it forces the timing gears to jump. This is a more catastrophic failure, though.
* Incorrect installation: If the timing gears were ever replaced, improper installation could lead to poor alignment and increased risk of slipping.
How a jump manifests:
When a timing gear jumps, the relative position of the crankshaft and camshaft is thrown off. This results in incorrect valve timing. The pistons might hit the valves (catastrophic), or at least the engine will run poorly, likely not starting at all or running very roughly, with very little or no power. You might hear a strange knocking sound.
Diagnosis:
Diagnosing a timing gear jump often involves checking the timing marks on the crankshaft and camshaft. If these are significantly out of alignment, it confirms the jump. You'll likely need specialized tools to accurately assess the timing.
Important Note: Timing chain/gear problems are very serious. Attempting to repair this yourself without proper experience and tools is strongly discouraged. Incorrect repair can lead to serious and expensive engine damage. It's best to consult a qualified mechanic.
