Timing failure

Failure

A pair of valves bent by collision with a piston after timing belt breakage. The engine was running at 4500 RPM.

Timing belts must be replaced at the manufacturer's recommended distance and/or time periods. Failure to replace the belt can result in complete breakdown or catastrophic engine failure, especially ininterference engines.^[4] The owner's manual maintenance schedule is the source of timing belt replacement intervals, typically every 30,000 to 50,000 miles (50,000 to 80,000 km).^[5] It is common to replace the timing belt tensioner at the same time as the belt is replaced.

The usual failure modes of timing belts are either stripped teeth (which leaves a smooth section of belt where the drive cog will slip) or delamination and unraveling of the fiber cores. Breakage of the belt, because of the nature of the high tensile fibers, is uncommon.^{[citation needed]} Correct belt tensionis critical - too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the cogs. In either case belt life will be drastically shortened. Aside from the belt itself, also common is a failure of the tensioner, and/or the various gear and idler bearings, causing the belt to derail.