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What Happens When a Timing Belt Breaks While Driving?

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In order for your engine to function properly, a timing belt aligns the crankshaft and the camshaft to ensure that they operate in precise synchronization. The belt is attached to a gear on the end of both of these shafts. As the crankshaft spins the pistons will rise in the cylinder of your engine. The camshaft which spins with it allows the valves to open and close. Timing is very important here because if the valves aren’t open then the pistons will hit them in the cylinder and cause damage to all three parts. If the timing belt breaks while you're driving, then the camshaft and a crankshaft will no longer be synchronized and depending on the kind of car you drive this could be extremely dangerous.

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What Happens When Your Timing Belt Breaks?


If your timing belt breaks while you're driving it can cause serious damage to your vehicle. The timing belt is a rubber-like belt that's usually made from some kind of composite material and infused with nylon threads to keep it strong.


The inside of the timing belt has teeth that allow it to grip the gears at the end of the camshaft and the crankshaft so that it stays securely in place when it is operating normally. If the timing belt becomes so weakened that it breaks however, it will snap off of these gears. The camshaft will not continue moving at this point, but the crankshaft likely will continue to rotate. This is a very serious problem.


The crankshaft in your vehicle rotates at about 1000 rotations per minute. When your timing belt breaks, there is no time for you to adapt to it or deal with the problem because of how fast that crankshaft is rotating. Because it moves that quickly the pistons will continue to rise in the cylinders. However, because the camshaft is no longer connected via the timing belt to the crankshaft it will not be operating. That means the valves at the top of the cylinders will not be opening to allow the piston to enter.


When a piston hits a closed valve or a partially closed valve it can severely damage the valve, the cylinder heads, and the piston itself. Because this happens so quickly this can effectively destroy your engine right away. You'll have no time whatsoever to react to the problem and do anything about it. That's why proper maintenance of your timing belt is so crucial. When it goes bad, there is nothing you can do about it. All you can do is deal with the after-effects.


There are a couple of things that can affect the outcome here, not the least of which is whether or not you actually even have a timing belt in your engine. The other issue to keep in mind is whether or not you have an interference or a non- interference engine.


What is an Interference Engine Compared to a Non-Interference Engine?


What happens when your timing belt breaks depends entirely on whether or not you have an interference engine or a non-interference engine. The big difference between the two types of engines is how the valves open. An interference engine is one in which the four stroke engine will open one or more of the valves to accommodate the piston as it rises into the cylinder. In a non-interference engine the Pistons do not go into the open house. This is the important difference between these two engines as it relates to how your timing belt works.


Because the timing belt synchronizes the camshaft in the crankshaft if the belt sales in an interference engine the camshaft will not be able to open the valve for the Piston to enter. However, the Piston is still going to rise into the cylinder. That means it's going to collide with the clothes valve and damage the can heads, the valves, and potentially damage to your whole engine.


When you have a non-interference engine in the timing belt fails the pistons will still rise but because they never enter the valve normally, even during perfectly fine operating procedure, no damage is going to occur when the belt fails in this case. The engine will stop working properly because the camshaft is no longer able to rotate at all, but you won't suffer the same extreme damage as a result of the belt failing. That's a crucial difference and will definitely end up saving you some money on repair bills if your timing belt fails.


Why Use Interference Engines at All?


If an interference engine is at such a risk of damage when the timing belt fails it might make you wonder, why we use interference engines at all in any kind of vehicle. The reason that interference engines are used, and they do tend to be used more often than non-interference engines, relates to the compression ratio that occurs in an interference engine. It's far superior to a non-interference engine. That compression ratio is directly related to the volume that is in the combustion chamber. So, in an interference engine you're getting a greater compression ratio which means better fuel efficiency and an overall better performance from your engine as a result.


 That doesn't mean a non-interference engine isn't a good quality engine either, it's just that manufacturers feel that they can get a better performance out of an interference engine. Choosing to manufacture a vehicle with an interference engine is there for risking the potential damage that can be caused if an engine belt fails with the definitive benefits that you get from the superior performance of that kind of engine. If you follow your manufacturer's guidelines and keep an eye on your timing belt, replacing it during scheduled maintenance and so on then the risk of this catastrophic engine failure is greatly minimized thus increasing the benefits of having an interference engine in the first place.


Obviously no one plans on having their timing belt fail however, so if it does break unexpectedly on you and you suffer this catastrophic engine failure there is little you can do about it but hey do you have some extensive repairs done on your vehicle.


Timing Belt vs Timing Chain


Not every vehicle uses a timing belt at all. Older vehicles were actually manufactured with timing chains back in the 50s and the 60s. These perform the same function as a timing belt however they are made of metal and look much like the chain you'll see on a bicycle. They are sturdier than timing belts and often last for much longer. While a timing belt should be changed every 60,000 miles to 90,000 miles, a timing chain can last for 200,000 miles or more. Generally speaking, a timing chain is built to last for the lifespan of the vehicle, while a timing belt must be maintained and replaced as part of scheduled maintenance.


Timing belts became the norm in vehicles some decades ago because it was a method of cost-cutting. Timing belts are cheaper to manufacture and lighter than timing chains, so they became the standard piece of technology used in many engines for a number of years. Nowadays, many manufacturers are going back to timing chains because of their increased reliability and strength. There are a number of manufacturers that don't use timing belts at all anymore, and others only use them in certain models. To know for sure which one, you have you'll have to check the owner's manual for your vehicle, or you can Google it and find out for sure if you don't already know. 


Signs and Symptoms of a Bad Timing Belt


Because the devastation that your engine will face when the timing belt breaks is so severe, you need to be on the lookout for the signs and symptoms that your timing belt is on the verge of failure. If you experience these then you need to get into a mechanic as soon as you can to have your timing belt looked at. As we said, there is no grace period between when your timing belt breaks and the damage that it will cause. It's an immediate reaction and if it happens while you're driving it could lead to a serious and potentially dangerous accident if you're not careful.


Engine Noises


When a timing belt begins to go bad in your vehicle it will make a distinct sound that is different from the noises you should be used to from under the hood. The timing belt will produce a fast-paced, repetitive ticking sound that it's not unlike the sound a roulette wheel makes when it's spinning. If you hear this sound, it's a good indication that your timing belt has already begun to wear down and is at risk of breaking sometime in the near future.


Your timing belt may also make a squealing sound if it begins to fail. Belts are known for this kind of noise when they go wrong, not just a timing belt or things like your serpentine belt as well. If the noises are intermittent rather than constant, it's a good sign that there's something wrong with a belt which may be the timing belt in your engine.


Engine Misfires


Because the timing belt is responsible for the precision timing of your engine, when it begins to fail then the timing will be thrown off. That could mean that the combustion reaction will either happen too early, too late, or not at all. When there's no combustion in the chamber at the correct time, that's an engine misfire. You'll know that's happening because you'll experience a distinct drop in overall engine performance, and you'll experience some shuttering or vibration in your vehicle as well, and potentially some noise from the engine.


When your engine misfires you lose power commensurate with the number of cylinders it occurs in. So if you have a four-cylinder engine and one cylinder misfires and that's a 25% drop in engine power. The more frequently this happens or the more cylinders it occurs in, the more power you're going to lose. 


Rough Idling


If your car is vibrating noticeably for no reason even when you're just sitting still, that's rough idling and it could be caused by a problem with the timing belt not gripping the gears as tightly as it should and slipping slightly.


Oil Leaks


Your timing belt has a timing belt cover over it that is bolted in place. If the bolts begin to loosen over time, then oil may begin to leak out. You could notice this in the driveway, or it could be contained within the engine compartment. However, if that happens, and especially if oil gets on the timing belt itself, it will not only weaken the timing belt but greatly increase the chances that it comes loose and slips off the gears.


Cost of Replacing a Timing Belt 


Getting a timing belt replaced is not a cheap job by any means. Replacement timing belts could cost you anywhere from $500 to as much as $2,000 depending on the make and model of your vehicle, as well as where you're getting it repaired. Even the belt on its own is going to cost between $100 and $300 to buy it at a site like autozone.com.


Even though getting a timing belt replaced is an expensive job, as you can see it's one that you definitely need to get done. If your timing belt breaks while you're driving any damage you can experience as a result can be even more costly.


The cost of replacing a damaged valve for instance can range from $900 to $2,000 on its own. If your pistons are damaged, then you can look at a repair bill from $1,000 to $3,000 or more. If the camshaft is damaged when the timing belt fails, then you may have to spend between $1,500 and $3,000 to get it replaced as well. Add in the fact that if your timing belt breaks while you're driving you will probably have damage to all of these parts and the repair bills can quickly get up to $4,000 or $5,000 and beyond.


The Bottom Line


Your timing belt is a simple piece of technology, but it is of vital importance to the overall operation of your vehicle. Make sure you know when to get your timing belt replaced according to the specifications in your owner's manual and don't let it go for too long. The damage that can be caused by a failed timing belt can't be underestimated not just in terms of money but the potential accidents that may happen as a result as well. 

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