Why It’s Important and How to Tell Which One Your Car Has
Timing belts and timing chains do the same thing: They connect the engine’s crankshaft to the camshaft, which opens up the valves of the engine. The valves let fuel and air into the engine, and exhaust out.
However, timing chains and timing belts are made of different materials (metal and rubber, respectively), installed in different ways, and have different maintenance costs (the most important characteristic for car owners).
We’ll explore what these car parts do, how they differ, and how much they cost.
What Do Car Timing Belts and Timing Chains Do?
Timing Chains and Belts Turn the Camshaft and Open the Engine Valves
Timing belts and timing chains connect the engine’s crankshaft to the camshaft, which opens up the valves of the engine. The camshaft makes one revolution for every two revolutions of the crankshaft, and as it turns, small oval lobes on the shaft, or cams, push against the valves to open them. The process follows the same principles as pedaling a bike, with the pedals being the crankshaft and the rear wheel being the camshaft; the timing chain or timing belt is the bike chain in this example.
Engine Valves Let Gas and Air Into the Engine, and Exhaust Out
Engine valves (each motor has at least two per cylinder) play a large role in the engine’s operation. During the first step in an engine’s cycle, the intake valves are open so fuel and air can enter the cylinders, while the exhaust valves are closed so that the mixture can’t escape. The intake valves then close, sealing the cylinders during compression and combustion. Afterward, only the exhaust valves open, so the leftover waste gases can be expelled. From that point on, the cycle continues in the same way.
Additionally, pulleys and tensioners are crucial to an engine’s timing system, since the parts are designed to keep the belt or chain from slipping and, in some cases, to drive other accessories such as the water pump.
Differences Between Timing Belts and Timing Chains
As you might guess, timing belts are closed belts, often made of reinforced rubber, and timing chains are metal chains. Chains came first, though, before advances in rubber technology made belts possible, and it wasn’t until the mid-1960s when Pontiac brought timing belts to mainstream vehicles.
Timing Belts Are Quieter and Less Expensive to Manufacture
Quieter and less expensive than chains, with some able to last as many as 100,000 miles, timing belts eventually became the go-to choice for automakers right up through the 1990s.
Timing Chains Last Longer, Saving Money in the Long Run
The pendulum has swung back around toward timing chains more recently, thanks to their longer lifespan. Automakers also have made numerous improvements in timing-chain technology, including reducing the amount of noise, vibration and harshness in today’s modern vehicles.
In fact, many companies expect their timing chains to last for the full life of their cars and trucks. That’s important, because timing belts aren’t expected to last that long, and replacing a timing belt can cost over $1,000.
Different Locations in the Engine
Timing belts are located outside of the engine, and timing chains are on the inside, where they can be lubricated by engine oil. In the cutaway image of the V8 engine above, the timing chain isn’t the twisting belt on the left, at the front of the engine. It’s barely visible just to the right of the belt’s big black exterior pulleys, where you can see the chain wrapped around gears on the crankshaft and camshaft.
How Do I Tell If a Car Has a Timing Belt or Timing Chain?
If you’re not sure about your specific vehicle, be sure to check the owner’s manual and follow any recommendations about timing belts or chains to the letter. Otherwise, it could soon be time for expensive repairs.
If you’re considering a new or used car and want to know whether it has a timing chain or timing belt, check the specs on the manufacturer’s website, or call your local service shop.
What Happens If I Don’t Replace My Timing Belt at the Right Time?
In the worst-case scenario, a broken timing belt (or chain, although they’re less likely to wear out) can quickly and entirely destroy a car’s engine. That’s because most of today’s engines are what’s known as “interference” engines. With these units, when the valves open and close, they move in and out of the same cylinder space as the top of the piston. The timing system ensures the valves are out of the way when the piston comes up. If the belt or chain breaks, the valves don’t move and will be smashed by the piston head. If this happens at high rpm, a valve can snap right off and become a fast-moving projectile that leads to catastrophic engine failure.
Needless to say, that’s something you want to avoid. Replacing a worn timing belt or chain is not a simple or inexpensive task. It can easily end up setting you back nearly $1,000. On the other hand, that’s still a lot cheaper than the alternative of replacing an entire engine after a broken belt or chain.
How Can I Tell If a Timing Belt or Timing Chain Needs Replacing on a Used Vehicle?
Things also can become especially tricky if you’re shopping for pre-owned vehicles, since it can be hard to determine when a timing belt or timing chain is wearing out.
You may be able to hear the engine misfiring, as the combustion process gets out of sync, and there can be other audible clues. Examples include a ticking sound after your turn off a car with a timing belt, or a rattling noise at idle from a vehicle with a timing chain. The former may leak oil as well, while with the latter, metal shavings can show up in the engine oil as a chain begins disintegrating. But as mentioned, you often get no warning at all.
This is why used-car shoppers should make sure they know if and when a timing belt or chain needs to be changed on a certain vehicle. Make sure to find out if this work has been completed before finalizing a purchase.
