An engines timing chain runs inside the engine and needs to be lubricated with oil. The chain is supported with plastic guide rails and tensioners.
Problems can occur over time with timing chains especially in higher mileage vehicles due to lack of oil changes, poor quality oils or low oil level. Failure of any part of the timing chain kit can result in sever engine damage if the chain is to slip a tooth or snap.
Usually a car with a problematic chain will give an early warning.Often, if the timing chain is worn the engine may feel sluggish, low on power or have troubles starting.
There may be a rattle from the engine especially when cold.This is the time to replace the chain before it leads to more serious damage.