Timing belts must be replaced at the manufacturer's recommended distance and/or time period. Failure to replace the belt can result in a complete breakdown and even catastrophic engine damage should the belt fail. The owner's maintenance schedule is the source of timing belt replacement, intervals typically every 60,000 to 90,000 miles approx. It is common practice to replace the timing belt tensioner and guides at the same time as the belt is replaced. The usual modes of timing belt failure are either stripped teeth (which leaves a smooth section of belt where cam sprockets will slip) unravelling of the fibre cores and snapped belt usually caused from seized components or exceeding date or mileage. Correct belt tension is critical - too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the sprockets. In either case belt life will be drastically shortened. Aside from the belt itself and also common is failure of the tensioner and/or various gear and idler bearings causing a belt to derail.