Some cars have a timing belt that’s hidden out of sight behind the engine’s front cover. You might not think that a belt sounds like a big deal—but the timing belt is a big deal because it can cause catastrophic engine damage if it fails.
It’s helpful to understand how the timing belt works and when it should be replaced. That way, you can avoid potential problems down the road.
The timing belt is a toothed belt (located behind the engine’s front cover) that’s used to keep the engine’s crankshaft and camshaft(s) in synch. You’ll find that the belt loops around the crankshaft and camshaft sprockets and also drives the engine’s water pump.
A typical timing belt is made from sturdy rubber (molded polyurethane, neoprene, or urethane). The belt usually has a high-tensile cord of fibers running its length and a facing fabric covering its teeth.
Before you can comprehend the role of the timing belt, it helps to have a basic understanding of the internal workings of the engine. Inside the engine, there is a crankshaft and one or more camshafts. The crankshaft is attached to the connecting rod and piston assemblies, whereas the intake and exhaust valves are operated by the camshaft(s).
The crankshaft and camshaft(s) must be kept in sync (“in time”) so that the pistons are at the correct point of travel when the valves open and close. Depending on the engine design, either a timing belt or timing chain is used to connect the crankshaft to the camshaft(s), thereby keeping the engine in time.
A tensioner pulley and one or more idler pulleys are used to secure and keep tension on the timing belt. It’s also important to note that the timing belt drives the engine’s water pump.
Below, you’ll find a timing belt diagram for a 2005 Honda Civic 1.7L. Keep in mind that this diagram is only an example. You can find the timing belt diagram for your vehicle by consulting a repair manual or an online repair database.
The crankshaft and camshaft(s) of an internal combustion engine must always be kept in synch. Depending on the engine’s design, this task is almost always accomplished with either a timing belt or a timing chain (some engines use timing gears, but that setup is rare and typically used in heavy-duty trucks).
Most engines built within the last ten years or so have a timing chain instead of a timing belt. But there are still many vehicles on the road with a timing belt under the hood.
As was mentioned, a timing belt is a toothed rubber belt that wraps around the crankshaft pulley, water pump pulley, and camshaft pulley(s).
The timing belt is considered a wear item because it’s made of rubber that can eventually stretch or break. As such, the timing belt requires periodic replacement. The belt should be replaced according to the vehicle manufacturer’s maintenance schedule.
Watch this video to get an idea of how timing belts work:
On the other hand, a timing chain is a metal chain made up of a collection of links. The timing chain wraps around the crankshaft sprocket and camshaft sprocket(s). Engines with a timing chain might use the chain to drive the water pump, or (more commonly) the pump is driven by the serpentine belt.
Timing chains are supposed to last the life of the vehicle (though that doesn’t always happen). Because of this, timing chains do not have a recommended replacement interval.
A timing belt can stretch or break for several reasons. Here are the most common:
Timing belts eventually wear out, which is why vehicle manufacturers recommend periodic replacement. If you don’t replace your car’s belt on time, it could stretch or break, potentially resulting in extensive internal engine damage.
If the timing belt tensioner or idler pulley fails, the timing belt can break as a result. The timing belt might also break if the water pump’s bearings fail.
Coolant from a leaking water pump or oil from a failed engine seal can contaminate the belt and cause it to fail prematurely.
A seized engine can create tension that causes the timing belt to snap.
A broken or stretched timing belt is bad news because it can lead to catastrophic internal engine damage. Most engines have what’s referred to as an interference design, which means the valves usually contact the pistons when the timing belt breaks.
If the timing belt fails, you might notice one or more of the following symptoms:
Note: Other problems can mimic a failed timing belt. You (or your mechanic) should perform a thorough diagnosis before conducting any repairs.
Your car won’t start if the timing belt breaks. Typically, the engine will crank faster than normal but refuse to fire up.
A stretched or jumped timing belt will typically result in the valves not opening and closing at the right time. As a result, the engine will experience a loss of compression, causing it to run rough and misfire.
Your car’s engine computer management system looks for anything that could lead to an increase in tailpipe emissions, including a misfire and other problems caused by a stretched timing belt. If the system determines there’s an issue, it turns on the check engine light and stores a corresponding diagnostic trouble code (DTC) in its memory.
Unfortunately, there isn’t an easy way to tell whether a timing belt is worn out and needs to be replaced. Even if you peel back the timing belt cover to perform a visual inspection, it’s hard to tell whether the belt is worn out. That’s why it’s important to follow the manufacturer’s maintenance schedule regarding timing belt replacement.
But if the timing belt is broken, you can often confirm this by removing the upper timing belt cover to perform a visual inspection. Some vehicles also have a dedicated inspection cover that you can remove to inspect the timing belt.
If you can’t get a peek at the belt, you can perform a compression test on the engine. Low compression on all of the engine’s cylinders often indicates a failed timing belt, as the video below demonstrates.
Another timing belt test method involves using an oscilloscope (if you’re lucky enough to have one), as outlined in the video below.
Replacing a timing belt is a big job that can result in significant engine damage if performed incorrectly. So, if you have any doubts about your automotive repair abilities, it’s best to leave the job to a qualified professional.
For an idea of what replacing a timing belt typically involves, here are some instructions outlining the job on a 2005 Honda Civic.
You’ll need the following tools when performing a timing belt replacement on a 2005 Honda Civic 1.7L.
2005 Honda Civic 1.7L Timing Belt Replacement Instructions
One thing to keep in mind is that most professionals also replace the water pump, along with the camshaft and crankshaft seals, as a preventative measure when replacing the timing belt. But in this article, we’re just going to focus on replacing the belt and automatic tensioner.
Note: The following are general guidelines for educational and entertainment purposes only. Consult your vehicle’s factory information for specific repair instructions and recommended safety procedures.
Check out the videos below for a visual representation of what the job involves.
You should always replace your car’s timing belt per the vehicle manufacturer’s service schedule. If you postpone replacement, the belt could break, potentially causing extensive (and costly) engine damage. You can find your car’s service schedule in the owner’s manual or supplemental service booklet.
Absolutely not. In many cases, a bad timing belt will prevent the engine from running altogether. But if the vehicle still runs, continuing to drive with a bad timing belt can damage the engine and other costly components.
You can typically expect to pay between $1000 and $2500 to have a professional replace your car’s timing belt. Of course, the exact cost of the repair will depend on various factors, such as the type of vehicle you have and the repair shop you choose.
If you have the tools and the know-how, you can save money by doing the job yourself with a replacement timing belt from CarParts.com.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
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I'm a mechanic and I found the article on timing belts to be truthful and accurate. I believe that if people use the information provided in it they will save a lot of engines from bent valves and therefore huge repair costs replacing them versus the relativley minor cost of replacing the timing belt at regular intervals. By the way I am a honest mechanic and have quit more than one shop that wasn't and I am truly sorry that there are people out there turning wrenches who are dishonest and giving my profession a bad name and violating the trust our customers place in us.
Thank you for the feedback, Daniel! We agree that if more people knew when to replace their car's timing belt, that knowledge would prevent a lot of headaches!
Thank you Mia Bevacqua, for an excellent, detailed and informative article on Timing Belts.
I know that I never want to attempt that repair myself.
Why would Honda, and other car makers, use the Timing Belt for the water pump? That doesn't seem logical. It just adds more unnecessary stress to belt. A serpentine belt is cheaper and easier to replace and won't damage the engine if it breaks. It's also in plain sight for easy inspection.