Signs of a Bad GM Timing Chainby Paul Novak
On most GM vehicles with V-8 or V-6 engines, a metal timing chain is used to connect the camshaft to the crankshaft. This causes the camshaft to move in synchronization with the crank, causing the camshaft to open and close the valves in the proper sequence and duration for the intake, power stroke and exhaust cycle. Because of this, pronounced slack in the timing chain can have a direct effect on the performance and fuel economy of the engine.
A worn timing chain introduces slack into the connection between the camshaft and the crankshaft. This causes the valves to open and close later than normal, resulting in reduced cylinder pressures and uneven firing of the fuel mixture. This can be felt as misses and uneven idling.
A worn timing chain may cause the cylinders to be unable to fully fill with a fuel and air mixture, reducing the amount of energy they can produce. This will slow down the response of the engine when the accelerator is depressed, and result in less power.
Abrupt Performance Change
A timing chain that receives sudden damage or extreme wear due to overheating or lack of oil may break teeth off of the drive gears on the camshaft, or jump positions on the gears. This can result in a severe loss of power, very poor idle, and the camshaft and crank becoming so far out of synchronization that the engine will not start.
A clattering noise coming from the front of the engine can be caused by a loose timing chain contacting the timing cover, or slapping against the gears on the crank and camshaft. A timing chain making noise like this is most likely near failure.
A loud popping hear under the hood is known as a backfire. A worn timing chain can cause this by allowing the timing of the engine's firing sequence to become so out of sync that the intake valve remains partially open during the power stroke, allowing the ignited fuel mixture to escape through the intake manifold.
A worn timing chain can be diagnosed by using a timing light to observe the relation of the timing marks on the timing cover with the marks on the crankshaft balancer. If the marks move back and forth in relation to each other instead of remaining in a steady position while the engine is running, the timing chain is most likely very worn.
- rusty chain image by Leonid Nyshko from Fotolia.com