The timing chain in an engine performs a very important function: it links the crankshaft and camshaft. Nylon gears and timing belts perform the same function on some makes and models. The intake and exhaust valves open and close in respect to the rotation of the crankshaft, which controls the strokes of the piston for firing. If the two become misaligned or the connection breaks as the result of a bad timing chain, the engine fails to run properly or won't run at all. The timing chain can make a variety of noises, and most often other parts of the engine are blamed for timing chain noise.
Place the vehicle in park or neutral and set the emergency brake. Raise the hood. Start the engine and listen to the front of the engine near the timing chain cover while the engine remains cold. A bad timing chain will often emit a rattling sound for a few minutes before the engine warms up, and then will lower in intensity or dissipate altogether after it warms up.
With the engine warm and idling, place the blade of a slot screwdriver with a very long-handled shank against the uppermost portion of the timing chain cover. Be extremely careful; you do not want the screwdriver to come in contact with any moving part, like a spinning belt or a fan blade. Also, tuck your hair back. Place your ear over the handle end of the screwdriver.
Listen for a metallic sound that resembles a rattling or scrapping noise. The sound can be intermittent or constant, but it will be a metal to metal contact. Such a noise will reveal a loose timing chain hitting the inside of the timing chain cover every time it rotates. You might also hear a metallic slapping noise. Don an automotive stethoscope and place the probe on the top or side of the timing chain cover. If you hear a rattle, metal to metal slapping or scraping coming from inside the cover, it indicates a timing chain noise.
Don the stethoscope and place the probe on the front of the valve cover, if you have a four-cylinder engine. Listen to the action of the rocker arm tappets. If they seem loud, move the stethoscope further down the valve cover and listen again. Move a few inches at a time. Listen for noisy lifters. If all the lifters sound noisy, it means that the timing chain has too much slack in it. This can work for V6 and V8 engines. Move the stethoscope slowly over both valve covers. If all the rocker arms seem noisy, it points to a stretched timing chain.
Determine if your vehicle has a single serpentine belt or individual belts running the separate components. Shut the engine off. For the serpentine belt configuration, refer to your owner's repair manual for the correct routing of the belt, or use the diagram on the top of the fan shroud.
Use a socket and breaker bar to attach to the centre bolt on the belt tensioner pulley. Turn it clockwise to unload the belt tension and then slip the belt off the pulley. Start the engine. Use the stethoscope to listen for noise at the timing chain cover. If you hear rattling or scraping noises, it will certainly be a bad timing chain, since you have eliminated the operation of the other likely components.
Use a socket and wrench to loosen the adjusting bolts on all the belt-driven components, if you have multiple belts. This includes the water pump, air conditioning compressor, alternator, fan pulley, power steering pump and smog pump. Remember the placement of the belts. Once the belts have been removed, start the engine.
Place the probe of the stethoscope on the top or side of the timing chain cover. If you hear a rattling or scraping sound, with no other noise being emitted from the engine, it indicates a bad timing chain. Do not run the engine excessively long with the belts off.