How does Timing Belt work? | Signs of bad Timing Belt

What is Timing Belt?

The timing belt is a component of the car engine that synchronizes the rotation of the crankshaft and camshaft in the engine’s lower and higher portions. The timing belt is also known as a timing chain or cambelt. This allows the engine’s inlet and outflow valves to open and close at precisely predetermined intervals during each round of the engine.

It serves as a link between the upper (cylinder head and valves) and bottom parts of the engine (pistons and crankcase).

timing chain

Working of Timing Chain 

The timing chain operates the engine’s intake and exhaust valves. These valves must open and close in precise coordination with the motion of the pistons.

The pistons drive the crankshaft. A sprocket on that shaft drives the timing chain which in turn rotates the camshaft to operate the valves.

When the engine runs, the motion of each valve is precisely synchronized to the arrival and departure of each moving piston. This synchronized event is called ‘correct valve timing’. It is the timing chain that makes this valve and piston coordination possible. 

Engine designers often use the timing chain to operate other engine components like the fuel pump, distributor, balance shaft(s), and/or the oil pump. Additional timing chain design features may include chain guides to constrain chain motion and reduce noise. 

Idler sprockets may be present to change the chain path of travel. And one or more timing chain tensioners may be employed to keep the chain taut and to account for eventual chain stretch. 

Depending on your engine configuration, it may have just one timing chain or several. While several timing chains complicate the system, the basic functionality remains unchanged.

What is the function of the Timing Belt?

A timing chain is responsible for controlling your pistons and valves, making sure they operate precisely when they need to inside your engine cylinders.

What’s the difference between a timing belt and a timing chain?

A timing belt is a heavy-duty rubber belt, with teeth along one side that fit into a series of pulleys and cogs that control your engine timing. If you open your bonnet, you should be able to see the rubber belts, or if not, a plastic case or cover where they’re sat.

A timing chain is a heavy-duty metal chain—something that looks a lot like a bicycle chain—but if you try to spot it when you lift your bonnet, you won’t. Your timing chain works inside the engine casing as it needs lubricating (with engine oil) to keep it in good condition and to operate as it should. It also requires oil to control the tensioners that keep it nice and snug.

Bad Timing Chain Symptoms

Following are the symptoms of a bad timing chain:

1) Stretched Timing Chain

Over time, the timing chain will stretch due to wear. Correct valve timing will degrade. This will be noted by an increase in fuel consumption, reduced power at low engine speeds, and an increase in roughness.

The stretched chain also may become noisy, producing a rattling or clattering sound. This sound will be evident with the hood open and it will vary with engine speed.

2) Engine Misfiring

Since the timing chain times the opening and closing of engine valves, any damage can unbalance the air-fuel ratio and result in a lack of power. It appears as a jerking motion and loss of acceleration.

3) Worn Timing Chain Sprockets or Idlers/Tensioners

This problem will display the same symptoms as a stretched chain. Additionally, idler and tensioner bearings may become worn leading to whirring sounds apparent during engine operation. This sound will grow louder with increased engine speed.

4) Contaminated Engine Oil

Another warning sign is finding metal bits in the engine oil. Metal parts from a damaged timing chain may break off and land in the oil. This finding must prompt the owner or mechanic to inspect the timing chain.

5) Timing Chain That Jumped from Its Idler or Tensioner

When a timing chain jumps off one of its sprockets, the engine will suddenly stop running. Loud clattering or grinding may also be noticed just prior to the engine quitting.

6) Worn Chain Guides

This age-related condition will result in a noisy chain operation. Chain rattles or clatter especially at low engine speeds may be noted.

5) Visually Broken Timing Chain

A broken chain will produce the same symptoms as the timing chain jumping off one of its sprockets. Considerable engine damage is very likely with both of these failure modes.

6) Check Engine Light

The Check Engine Light may come on if valve timing exceeds certain preset limits and/or exhaust emissions go out of spec. A CEL warning necessitates immediate evaluation by a qualified service technician.

Ignoring this warning can lead to severe damage to your engine and associated systems. For a timing chain failure, this warning will occur for some but not all makes of automobiles.

Timing Chain advantages and disadvantages

Advantages of Timing Chain

  • A chain offers superior strength, giving it a far longer lifespan. Hopefully, with proper care and maintenance, a timing chain should last the lifetime of your vehicle.
  • Maintenance is simple—keep up with your oil changes and consider a one-off check at the 125k-mile mark.
  • A metal chain is heat resistant, so isn’t vulnerable to changing conditions in the weather. A rubber belt can freeze in low temperatures, affecting performance.

Disadvantages of Timing Chain

  • A timing chain is much heavier than a rubber timing belt. This increases fuel consumption, and in turn, affects your fuel economy, adding to pollution, and impacts engine power.
  • A timing chain is far noisier than a timing belt.
  • Due to the extra weight, a timing chain is often only available for use on larger engine cylinders.
  • They’re considerably more expensive to replace and to work on.
  • A timing chain requires constant lubrication.

FAQ Section

What causes a timing chain to break or wear?

Over time, the timing chain stretches due to internal component wear. The chain tensioner or the guides that are connected to the timing chain may wear out as well, causing the timing chain to fail completely. If the chain fails, the vehicle will not run at all.

Overly frequent continuous operation of the engine at or near its redline, i.e., maximum speed (at track day events, for example) may overheat and excessively wear the timing chain, guides, and sprockets. This could lead to chain breakage.

Should I also replace sprockets?

Yes, it is recommended that all components of the timing system be replaced at the same time. Using a worn sprocket may result in the chain not meshing with the worn sprocket, which could result in poor engine performance.

What is the Timing Chain Replacement Cost?

The replacement cost of the timing chain depends on the vehicle model, labor cost, and the type of brand. The average replacement cost of the timing chain is $280 to $1,600.

In most cases, you can expect the job to cost at least $750. However, if you have a complicated engine, it can cost several thousand dollars. The cost of the parts is between $40 to $410. The rest is all the cost of labor. 

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