A few seconds of chain rattle on a cold start, later a permanent noise; the chain stretches and the tensioner does not hold it. If the chain jumps, the engine is badly damaged inside, and the repair is a rebuild. The tensioner is driven by oil pressure, so it does not hold with the engine stopped: a car left rolling in gear is the typical trigger for the chain jumping.
What to check
- Start it cold, and in the first 2 to 3 seconds watch for the rattle from the chain side
- Ask whether the chain and the tensioner have been replaced, and ask for the invoice
- Check the oil change history in the service book: stretched intervals speed up the wear