The camshaft(s) on many Single Over Head Cam (SOHC) and Double Over Head Cam (DOHC) engines are driven by the crankshaft via a timing belt. The camshaft operates the valves, and valve opening and closing must be perfectly synchronized with the up and down movement of the pistons for optimal engine performance. The timing belt drives the cam(s) and keeps the engine precisely timed with the aid of a tensioner and idler pulley(s).

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At one time, chains and gears were the camshaft drives of choice, but as overhead cam engines became more and more prevalent, engineers found that belts were more easily routed, ran quietly, didn’t require lubrication, were less expensive, and reliable. The last factor has progressed even further, with improved materials stretching belt replacement intervals from about 30,000 miles when they were first used, to 60,000 miles or more today.

But such improvements in reliability shouldn’t inspire complacency. The manufacturer’s replacement interval can be found in your owner’s manual and this maintenance should not be ignored. A timing belt can break without notice and when that happens your engine will stop. Even worse, many engines are “interference” engines, and on these engines the pistons will contact the open valves, causing expensive engine damage. But a belt doesn’t have to fail completely to affect engine performance. Belt damage or a worn tensioner can cause the belt to jump time, resulting in poor performance or an engine that won’t run at all.

If access to the belt is possible, it should be inspected for cracks, missing teeth, frayed or exposed fiber reinforcement, and oil or coolant contamination. Any of these conditions are cause for belt replacement regardless of mileage, but even if the belt looks perfect at the recommended replacement mileage, it should not be reused. Although it is common practice to reuse crankshaft and camshaft pulleys, these components should be inspected for wear and imbedded dirt that could interfere with the new belt.

However, components like automatic tensioners and idler pulleys should always be replaced when a new belt is installed to ensure proper engine performance. On many engines the timing belt also drives the water pump. Although it may appear OK when the belt is serviced, its negligible cost compared to the cost of the labor to access it makes pump replacement with the belt the smart move. And it would be a shame to have to do the job all over again if the old pump were to fail shortly afterward. Our kits provide everything needed with one part number: belt, tensioners, idler pulley(s), water pump, and seals and gaskets.

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Timing Reviews

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2005 Volkswagen Beetle
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