Timing belt

Toyota describes the timing belt as facilitating the precise coordination of the crankshaft and camshaft. That coordination is what keeps valve movement matched to piston movement. Being rubber, it is a scheduled replacement item: Gates, an OE belt maker, states that timing belts are a critical part of any engine maintenance program and must be replaced at the specified interval determined by the belt manufacturer or original equipment vehicle manufacturer.

It is one of the few maintenance items with a defined interval and a documented consequence for missing it, so service records showing the replacement are worth locating on any belt-driven engine.

In the owner's manual maintenance schedule, on service invoices, and in the recent-work section of listings.

The serpentine or drive belt runs accessories on the outside of the engine; the timing belt sets valve timing inside it. Some engines use a chain instead.