Types of Timing Chains
There are two types of timing chains in use today: link chains and roller chains. These constructions date back to the late 19th century.
Link chains consist of many precision links made of flat, hardened alloy steel secured by pressed pins. The shape of each link corresponds to the drive face of both the crankshaft-driven sprocket and the camshaft-driven sprocket.
The link shape is intended to ensure smooth engagement of each sprocket. For this reason, the design is sometimes called a “quiet chain.”
Roller chains look similar to bicycle chains, but are larger, stronger, and more durable. Their design allows them to run around smaller diameter sprockets, requiring less space than link chain designs.
For light vehicle engines, roller chains can be in a single-row configuration (like a bicycle chain). Larger, more powerful engines require a double-row design. The roller chain engages with precision alloy steel sprockets.
The timing chain is usually housed in a housing at the front of the engine. This housing is sealed, the chain is lubricated, and wear particles are flushed away from the engine oil system.
Timing chains should not be confused with timing belts, which perform the same function but have a very different design and failure mode.
How a Timing Chain Works
The timing chain operates the intake and exhaust valves of the engine. These valves must open and close in precise coordination with the movement of the pistons.
The pistons drive the crankshaft, which has a sprocket that drives a timing chain that rotates the camshafts to operate the valves.
When the engine is running, the movement of each valve is precisely synchronized with the arrival and departure of each moving piston. This synchronized event is called “correct valve timing.” This adjustment of the valves and pistons is made possible by the timing chain.
Engine designers often use the timing chain to operate other engine components such as the fuel pump, distributor, balancer shaft, and oil pump. Other timing chain design features may include chain guides to limit chain movement and reduce noise.
Idler wheels may be present to reroute the chain, and one or more timing chain tensioners may be used to keep the chain tight and compensate for chain stretch. Depending on the engine configuration, an engine may have only one timing chain or multiple timing chains. Multiple timing chains make the system more complex, but the basic function remains the same.
What causes timing chain noise?Timing chain noise can occur even before the chain has completely failed. Typical causes of chain noise include problems (1) to (3) in the previous section. Additionally, timing chain noise can occur if the tensioner is not adjusted correctly (too loose).
The moving chain will start to hit and rub against nearby engine parts. If not addressed immediately, debris particles can find their way into the oil pan and clog the oil inlet, partially or completely clogging the oil filter.
Please note that such abnormal noises can also be a precursor to a chain failure. If you hear such abnormal noises, we strongly recommend having the problem diagnosed by a qualified service technician. What causes a timing chain to break?
Timing chains can break for the following reasons:
1. If the chain has an adjustable tensioner, it may have been adjusted too tight during routine maintenance. Setting it too tight overloads the chain, guides and sprocket structures, causing accelerated wear. This wear can lead to the chain breaking.
2. As the vehicle ages, wear and tear from normal life on the chain and its components, as well as wear on the guides and sprockets, can cause chain breakage.
3. Excessive continuous operation of the engine at or near maximum speed (e.g. during track events) can cause overheating and excessive wear on the timing chain, guides and sprockets. Can lead to chain breakage.
4. Failure to regularly change engine oil and filters can adversely affect the life of your timing chain. Old engine oil contaminated with sludge can accelerate wear on the timing chain, guides and sprockets. It can even lead to chain breakage.
Diligent regular maintenance as recommended by the manufacturer can help extend the life of your timing chain and your entire engine. Regular oil and filter changes are especially beneficial.
Using full synthetic oil (rather than conventional oil) of the proper viscosity will further reduce engine wear and extend overall life. Consult your owner’s manual for maintenance and lubrication recommendations.
When should my timing chain be replaced?Timing chain systems are designed to last the life of the vehicle. Routine chain replacement is not necessary.
However, if abnormal noise symptoms or engine operating characteristics (1), (2), (3), or (6) described above under “Symptoms of Timing Chain Failure” are present, evaluation by a qualified service technician is required.
Replacing a worn timing chain is an expensive service. However, this expense is far better than a complete overhaul or engine replacement, or perhaps even a new car, that may be necessary if the chain fails.
