It's rarely the chain itself
In the vast majority of cases we see, the chain material itself isn't the problem — it's the hydraulic tensioner responsible for keeping it correctly tensioned. Tensioners rely on oil pressure and wear over time; once they can no longer maintain proper tension, the chain develops slack, which is what produces the characteristic rattle and, eventually, incorrect valve timing.
What accelerates the wear
- Extended or missed service intervals, and the resulting reduction in oil quality
- Oil dilution on diesel engines, which thins the oil and reduces lubrication at the tensioner
- Frequent short journeys that don't let the engine reach full operating temperature
- Known design weaknesses in certain tensioner generations, which is why some manufacturers and engine families are more commonly affected than others
What happens if it's left too long
As slack increases, the chain can skip a tooth on the sprockets, throwing valve timing out — this alone can cause serious drivability issues and, on interference engines, the risk of piston-to-valve contact. In the worst cases, a badly worn chain can snap completely, which on most engines causes catastrophic internal damage requiring a full rebuild rather than a straightforward chain replacement.