Timing belts are a maintenance item on engines that have them, but what about timing chains? On most overhead cam engines that use a timing chain to turn the cams, there’s usually some type of chain tensioner or adjuster to keep the chain tight and to compensate for stretch as the chain ages. But on pushrod V6 and V8 engines, there is no chain tensioner to compensate for chain stretch. Consequently, after tens of thousand of miles, the chain loosens up, starts to make noise as it rattles against the front cover, and causes cam timing to retard. At this point the timing chain needs to be replaced.

The main cause of timing belt wear is heat - caused by both friction of the belt moving, as well as high engine temperatures.

On some engines, the valvetrain uses both types of drives: a timing chain and a pair of belts. Chevy’s 3.4L DOHC V6, for example, uses a timing chain to drive an intermediate sprocket that also drives two belts (one for each pair of overhead cams). This type of setup doubles your opportunity to service the cam drive system. You can replace the timing belts for preventive maintenance, and you can replace the timing chain if it has stretched or is worn.

When Parts Wear Out
Timing belt...