The marvel of the modern automobile—it’s something to behold. A car is manufactured out of roughly 30,000 parts. An internal combustion engine alone, for example, uses thousands of parts to assemble. Despite its complexity, a car’s operation can be completely derailed by something as simple as a timing belt.
So what does a timing belt do and what happens if there’s a problem?
What is a timing belt?
A timing belt is a circular reinforced rubber or polyurethane belt with teeth on the inner surface and a flat outer surface. Belts are reinforced with strands of tough materials such as Kevlar, steel cord and twisted fiberglass cord to prevent stretching and deterioration. The surface that contacts the engine’s cogs is sometimes covered in nylon.
It’s important to note that not all cars have timing belts. Some operate with timing chains instead. Although they’re tougher and longer lasting, chains also add weight and manufacturing cost, which is why more automakers today use timing belts.
What does a timing belt do?
The timing belt uses the crankshaft’s rotation to precisely time the camshafts as well as opening and closing valves in the cylinder head. If the timing is off by even one of the belt’s teeth, it won’t work as powerfully and efficiently as designed, and on some cars the engine might not run at all. To understand its purpose requires a basic understanding of how an engine works.
In an engine, three things are necessary to run: fuel, air and ignition or spark. All three of these items have to be precisely timed or the engine could be destroyed. For example, fuel and air need to be injected into the combustion chamber when the piston is moving downward during the intake stroke, and the spark plug needs to fire when the piston returns to the top of the compression stroke. That needs to be repeated for each cylinder and for every engine revolution without fail.
What happens if a timing belt breaks?
What is a timing belt going to do if it suddenly (or not-so-suddenly) snaps? There are two scenarios in which a timing belt breaks, and it depends on the type of engine you have.
In a noninterference engine, the moment the timing belt breaks, the engine will stop running and won’t restart. The cylinder head has no input from the camshaft, and until the belt is replaced, your car is out of commission. Typically, no additional repairs are required other than having your car towed to the shop and having a new timing belt installed.
What does a timing belt do in a car when it breaks in an interference engine? In this situation, the engine also quits the second the timing belt snaps. The difference, though, is the potential for additional damage. The term “interference engine” refers to an engine in which the cylinder head valves open into the path of a piston.
There’s a very good chance that one or more pistons will hit valves in their respective cylinders, causing serious damage that must be repaired before the engine can run again. It’s going to take more money and time to repair because there can be pistons, valves, cylinder heads, fuel injectors or a complete engine to change.
When should I replace my timing belt?
The typical service interval for timing belts ranges between around 60,000 and 100,000 miles, but every vehicle manufacturer sets their own service interval by model. For your particular vehicle, you’ll find the exact interval in the owner’s manual or maintenance guide. If you don’t have a printed copy, automakers offer the documents you need by year, make and model in the “Owners” section on the website.
Just as with any rubber parts on your car, like the serpentine belt and tires, degradation will happen. It can be simply from time and countless hours in use, or a problem with a timing belt can occur from weakening timing belt tensioners or contamination from a leaking engine oil seal. You can’t plan for problems due to a mechanical failure, but you can schedule a maintenance visit to change the timing belt.
This begs the question, “Can you inspect a timing belt’s condition before it fails?” Yes, it is possible to check a timing belt prior to replacing it, but it’s a labor-intensive process. The timing belt is tucked behind the engine front cover along with the crankshaft and camshaft pulleys and, in most cases, the water pump. It can take a technician several hours to remove the parts attached to the front cover to check the belt, then reinstall all of the parts. It simply isn’t a viable option on most cars.
You’ll almost never hear, see or feel symptoms prior to timing belt failure because it’s tucked away and out of sight. That’s why it’s so important to follow the manufacturer’s recommended replacement interval rather than wait for signs of a problem.
How much does a timing belt cost?
The average timing belt kit begins at under $100, which includes the belt, idler pulley, water pump and gasket, but it can run up to a few hundred dollars or higher. But the larger cost is usually the labor.
Labor prices across the nation vary greatly, from around $50 per hour to $215 or higher per hour So let’s assume a middle-of-the-road price of around $125 per hour. The labor to change a timing belt can be around two hours for a 2011 Mitsubishi Outlander V6 for a labor price of around $250, while a 2017 Chevy Cruze takes around 5.8 hours, tallying up to $725 in labor alone for the job. A more common time frame is somewhere in between. A 2007 Honda Accord, for example, takes about four hours to change the timing belt, or around $500 in labor.
Between parts and labor, a timing belt replacement will run you anywhere from around $350 to $1,000, and the odd vehicle might be even more. Once the technician has the front engine cover off, they’ll be able to identify if anything else needs attention at the same time, like a leaking front crankshaft oil seal or a camshaft oil seal, so there could be additional costs.