Automotive engines rely on the combustion of volatile gases to create energy that moves the mass of the crankshaft. This crankshaft movement is transferred to the wheels through the drive train to move the vehicle. The process of energy creation and crankshaft movement is controlled through the complex interaction of components that rely on precise timing to work properly. The critical link in this process is the timing chain. A loose timing chain disrupts this timing.
When a timing chain becomes worn it stretches. The increased length of the chain creates slack in the connection between the camshaft and the crankshaft. This slack changes the timing of the valves opening and closing, causing a reduction in the cylinders' pressures and incomplete firing of the fuel and air mixture. This results in uneven firing of the cylinders, which is noticed as misses and a rough idle.
A loose timing chain will cause the valves to open and close at the wrong time. This results in an improper fuel mixture in the combustion chambers and less energy produced by the combustion process. This is noticed as poor throttle response and reduced overall power.
A loose timing chain has excessive slack. This slack allows the chain to move around on the gears connecting it to the camshaft and the crankshaft. A severely loose chain may contact the timing chain cover or jump around on the gears. This movement results in a clattering noise coming from the front of the engine.
A severely worn timing chain can cause the timing between the opening of the valves and the ignition of the fuel mixture to become so out of synchronisation that the mixture is ignited while the valves are still partially open. The explosion from the ignited gases creates pressure that escapes past the open valves, resulting in a loud popping noise that can be heard through the intake manifold or the exhaust.