The typical rattle on start-up
When starting from cold, a metallic clatter or rattling noise lasts for one to three seconds before disappearing. This is often the timing chain slapping: while oil pressure builds up, the hydraulic tensioner can no longer hold it correctly.
The likely causes
- Timing chain stretched by wear, along with its guides and slippers.
- Worn hydraulic tensioner that bleeds down when the engine is off.
- Wrong oil grade or oil changes left too long, which accelerate chain wear.
- Less commonly, hydraulic tappets bleeding down: a light ticking noise from the top of the engine.
Why you should act quickly
A stretched chain can jump a tooth or even snap. On most modern engines, the valves then strike the pistons, resulting in bent valves, a damaged cylinder head, and sometimes holed pistons. Replacing the timing chain kit in good time avoids a far more costly repair.
Can you keep driving?
For a short while, yes — provided you avoid high revs. If the noise lasts longer, also appears when the engine is warm, or is accompanied by misfires, get it seen to promptly.
If the chain has already jumped
If the engine has cut out suddenly and won't restart, or has lost compression following a chain jump, the internal damage is often extensive. A reconditioned engine on an exchange basis, supplied bare and warranted for up to 24 months, is generally the more sensible option over an internal rebuild.
