Timing chain rattle at startup
Brief metallic rattle on cold start, lasting 1–3 seconds, from the front of the engine.
M117 uses a duplex timing chain with a hydraulic tensioner. Startup rattle = tensioner not pumping up fast enough OR slack chain. Ignore at your peril; a snapped chain destroys the engine.
What the diagnosis checks
- How long is the rattle — under 2 s, or longer?
- Have you measured chain stretch at the cam tower?
Possible causes it points to
- Tensioner draining down overnight
- Chain stretched beyond limit
- Measure stretch first
Parts for this job
Maintenance basics: oil, plugs, filtersBackground reading
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