Things to Know About the Engine Timing Belt - Subaru Service Questions in Olympia, WA

Timing belts and chains are commonly misunderstood. While many people have heard the horror stories of a snapped timing belt destroying an engine, that's often the extent of what people know about this component. At Hanson Subaru, we want you to have important information about your vehicle. This means that you should be able to know more about how it functions and the best way to take care of it. With that in mind, we've compiled five things that are important to know about the timing belt or chain in your Subaru.

Timing belt

5. Do All Vehicles Have Timing Belts?

No. While timing belts are incredibly common, there are many vehicles that use other components. Timing gears and timing chains were used before timing belts were developed. Though timing chains fell out of favor in the 1980s, they've experienced something of a revival lately. In fact, if you're driving a relatively new Subaru model, chances are your vehicle is equipped with a timing chain instead of a timing belt. Chains are heavier and louder than belts, but they're also much more durable and longer-lasting. Unless there's a severe problem, a timing chain will never need to be replaced, and regular oil changes are all the service it will generally need.

Dual-cam valvetrain

4. What Does a Timing Belt or Chain Do?

In short: the timing belt or chain synchronizes the movement of the crankshaft with the movement of the camshaft or camshafts.

We'll break this down a bit to explain what it means. When your engine is running, a mixture of fuel and air is let into the combustion chamber, or cylinder, by way of an intake valve. After the intake valve closes, a piston inside the cylinder moves up to compress the fuel and air mixture. Once it's compressed, a spark plug will create a small spark that ignites the mixture. The force of the combustion will push the piston back down the cylinder, after which an exhaust valve will open up to let the exhaust gases from the process exit the engine.

So where do the crankshaft and camshaft come in? The crankshaft is what the pistons are attached to, and it converts the linear energy of the moving piston into rotational energy. Camshafts open and close the intake and exhaust valves. In order for the combustion process to work, everything has to be timed perfectly, and that's the job of the timing belt or chain.

3. What Happens When a Timing Belt Breaks?

It depends on what kind of engine your vehicle has. Older engines were free-running, which means that the piston never moved far enough into the cylinder that it risked hitting the valves. By comparison, most modern engines are what's called interference engines. These engines are even more efficient, because the pistons can compress the fuel and air even further. However, this means that the pistons, when fully extended, occupy the same space that the valves would occupy when open.

If a timing belt breaks in a free-running engine, the car will simply stop running. But in an interference engine, things get trickier. Since the valves and the pistons will no longer be synchronized, a piston could strike an open valve, causing massive damage.

Person replacing timing belt

2. Why Is Replacing a Timing Belt Expensive?

While the timing belt itself is a relatively inexpensive component, you'll find that replacing it is one of the more expensive services your car might need. This is due to the fact that replacing a belt is labor-intensive. Since the belt is buried within the engine, the technicians will need to disassemble a large part of the engine itself just to get to the belt. After the engine is dismantled, they'll check various components around the belt before removing it. At this point, they'll also usually replace the water pump, tensioner, and idler pulleys. After putting the new belt on, they'll set the timing and test it to make sure that nothing is wrong. After this, they'll put the engine back together.

As you can imagine, this takes hours of labor. While the belt itself may not cost much, the skill, time, and effort to replace it is extensive.

1. Are There Symptoms of a Bad Timing Belt?

No. Or, to be more precise, there are no symptoms that you can rely on. A timing belt that's becoming worn out may cause a ticking noise. However, this is just one of many potential causes of ticking, and it won't even happen consistently. Many times, the belt will simply snap with no warning. Because of this, it's absolutely vital to have the timing belt changed at the intervals recommended by the manufacturer.

Hanson Subaru

2300 Carriage Loop SW
Directions Olympia, WA 98502

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