The camshaft(s) in a four-stroke engine are driven by the crankshaft at half crankshaft speed. The cam(s) and crank must be perfectly synchronized as they rotate so that the camshaft operated valves open and close precisely in time with the up and down movement of the pistons. Timing gears or timing chain and sprocket sets drive the cam on all Over Head Valve (OHV) engines, while chains or belts and sprockets are used on Over Head Camshaft (OHC) engines.

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A matched set of gears on the crank and cam are the simplest and most durable form of cam drive, but gears are heavy and noisy, and typically only used on low revving engines. Because the cam is so close to the crank on an OHV engine, and the chain is so short, only the basic cam and crank sprockets and chain are needed to drive the cam, but tensioners and chain guides are required for the much longer OHC timing chain.

There are two types of timing chains, the inverted silent tooth chain, which is favored by many OEMs for its quiet operation, and the lower friction but noisier double roller chain, the preferred chain for performance applications. Both types can suffer from the common timing chain malady, chain “stretch”, which isn’t stretch at all but rather elongation from the cumulative wear of the chain’s pins and links. An elongated chain will retard valve timing, and it can rub against the timing cover and cause a rattling noise and debris to be circulated throughout the engine.

The hydraulic tensioner is crucial to timing chain performance on OHC engines. However, not changing the engine oil regularly or using the wrong weight oil can negatively affect tensioner operation, resulting in too much chain slack, particularly at critical times like engine startup. A “stretched” chain and retarded valve timing will result in poor performance and fuel economy, but extreme looseness and/or a worn tensioner and chain guides can cause the chain to jump time, resulting in performance that is even worse or an engine that won’t run at all.

Whatever the configuration of your engine’s cam drive, we have the parts to restore precision valve timing and performance, and quiet operation. Timing gears, and timing chain and cam and crank sprockets, should always be replaced in sets. On OHC engines, the tensioner(s) and chain guides should be replaced at the same time as the chain and sprockets. And if the chain has rubbed a hole in your timing cover or it’s otherwise damaged, there’s no need to go to the dealer because we have OE spec covers right here on our digital shelves, along with gaskets and everything else needed to complete installation.

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2001 Chevy Tracker
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