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Why Do Engines Knock? – What You Need To Know!

Why Do Engines Knock? – What You Need To Know!

While an engine knocks creating noise, your nerves “knock”, creating frustration within you. So why do engines knock and what can you as a car owner do about it? We have the reasons as well as helpful advice for you now! 

Auto Repairs Are EXPENSIVE

What Are Some Of The Most Common Reasons That An Engine Knocks? 

Your engine is knocking and now it’s time to open that door to a potential issue. What will it cost you to get that knocking taken care of? Why in the world is your engine knocking? Once your engine begins to knock, then there is a problem Check out some of the most common causes of an engine knocking that can provide answers you need. 

Faulty or Bad Pulleys and Belt Tensioners 

One possible source of engine knocking may not be coming from your vehicle’s engine at all. That frustrating knocking sound could be coming from your vehicle’s accessory belt. As your vehicle engine runs, there is a belt that turns, which is connected to an array of pulleys that are located throughout the engine bay. The belt has to operate under the correct amount of tension. The precise tension ensures a quiet and smooth run. Should the belt become stretched out, this indicates that the tensioner isn't working correctly. It could also mean that one of pulleys has become bent out of shape. All of these circumstances give the perfect condition for clicking, slapping and even rattling noises. Thankfully, a replacement of the belt can remedy this issue. You may even be able to just adjust the tension. Another remedy can also be to replace the accessory pulley or the faulty tensioner. 


Bearings That Are Worn/ Rod Knocking 

Another kind of engine knock is that of a rod knock. When the vehicle’s pistons go up and down in the vehicle’s engine, then turn the crankshaft that ultimately sends power to the vehicle’s wheels. The rod bearings accelerate efficient piston movement. But they can also experience wear and tear as time progresses. When the bearings wear out, the pistons will begin to rattle against the vehicle’s crankshaft.  That rattling will sound very similar to a frustrating knocking sound. To fix the issue, you may need a replacement of your bearings. There may also be a need to fix the crankshaft or the pistons. All of the fixes can involve intricate labor and work for a mechanic or auto professional. 


Octane Levels Are Low

With a smooth-running engine, the fuel/air mixture burns up in a single, controlled detonation that is located inside each cylinder. A detonation knock is a is a noise you’ll hear when the fuel/air mixture located in the cylinders, is detonating in several places at one time. Parts of the fuel/air mixture may begin to ignite way too early. Once the fireballs collide, a knocking noise is created. Should you have a performance-tuned engine that has a rating for high-octane fuel, you may have an engine knock, should you use fuel that has a low octane rating. Higher octane fuels tend to burn more evenly while resisting knocking sounds. So, if you’re putting regular unleaded gas in your car, but your car requires premium fuel, then this is the reason you have a knocking sound.  

Bad Spark Plugs 

Our vehicle’s spark plugs are quite important for our car to operate at optimum performance. Another way to put it, the engine’s spark plugs transport the electric spark which ignites the cylinder’s air/fuel mixture. Just like other parts of a car, spark plugs break down and age as time progresses. Lots of auto manufacturers suggest getting new spark plugs every 30,000 miles. Keep in mind that your vehicle’s spark plugs will perform, depending on the quality of spark plug. You want to make sure that you purchase quality spark plugs, and have a qualified mechanic install them, for stellar performance. If you decide not to use a manufacturer recommended spark plug, or you have spark plugs that are “living in their last days”, then this may be the reason that you have the knocking sound. 


There are Carbon Deposits 

All fuel that is sold in the United States is required to include carbon cleaning detergents- which prevent carbon deposits from clogging the vehicle’s cylinders. Despite such, there are some deposits that still form. Once you have those carbon deposits, there is now limited room for air and fuel to reside. This also leads to unwanted compression too. Excess or extra carbon buildup can lead to huge issues that can not only damage your engine’s cylinders, but also diminish fuel efficiency This means more trips to the gas station to fill up.  To remedy this issue, you want to get your cylinders cleaned by a qualified mechanic. 


How Can I Prevent Engine Knocking? 

You know the reasons that your engine is knocking. Now the question is how do you prevent it? 


Use the Correct Octane 

As car owners, we are all about saving money- the same is true for going to the gas station. But if you have a car that cannot take an 87 octane, then you shouldn’t use it. You may save a few dollars at the pump, but you’ll soon be shelling out money to fix engine knocking, all because you want to use a cheaper octane. Always remember: the higher the octane number, the more stellar the fuel’s ability to resist any kind of detonation. Although lots of vehicle engines are OK to use an 87 octane. But you may have a vehicle that has a higher compression- which requires that you use an 89-octane rating or even higher. So, pay more at the pump, and keep your beloved “baby” out of an auto bay for engine knocking. 

Check Your Ignition Timing 

An over-advanced ignition timing may cause cylinder pressures to rise far too quickly than they should. This can lead to detonation. So, you can view your stock specifications and reset your timing. Should that not work, then you can also turn back the timing just a few degrees. You may also find that a careful re-calibration the distributor advance curve may help. That re-calibration can help to keep detonation at bay.  

Control And Manage Your Boost 

When it comes to controlling engine knocking, you want to control the level of boost that is in a forced induction engine. This is critical in maintaining the health of your car. Excessive boost can lead to detonation. Therefore, you should either tailor your engine to handle more boost, or just scale it back all together. 


Evaluate And Monitor Your Mixture 

Lean fuel and air mixtures are far more prone to detonation. Therefore, you need to monitor your fuel and air mixture- and adjust them accordingly. A lean condition could indicate a bigger issue such as vacuum line air leaks or even gaskets that fail to perform as they should. A lean condition can also be caused by fuel injectors that are dirty. Clogged carb jets and a restricted fuel filter may also be culprits. Do you have an engine that is experiencing rough idle or hesitation?  Then a lean fuel condition could be to blame. 


Check for the Root Cause of Carbon Deposits 

Another way to avoid engine knocking, is to look for the source of carbon deposits. Carbon deposits are one of the most common causes of detonation in engines built for high-mileage. The bottom line is this: carbon deposits can collect quickly in the combustion chamber as well as on top of the vehicle’s pistons, till the overall compression of the engine is changed. Those carbon deposits can also produce an insulating effect, which slows the heat transfer from the cylinder head, to the combustion chamber. If enough deposits build up, then you have detonation. Therefore, you want to check the source of the carbon deposits. You can remove the carbon deposits with a quality chemical cleaner. You can also remove the carbon deposits with a scraper or even a wire brush. 


Check Your Knock Sensor 

If you are experiencing engine knocking, then you may have a faulty knock sensor.  Your vehicle’s knock sensor does certainly respond to vibrations at a various and specific frequency ranges. When the frequencies- generally produced by detonation- are on the radar, the knock sensor tells the computer of your car to retard or wait on ignition, till the detonation ceases. Are you experiencing a “check engine light” that is illuminated on your dash alongside your knocking engine? Then you have a bad knock sensor (among other issues). You may be able to evaluate your onboard computer system with a reading of the engine’s trouble code. You may also be able to evaluate your knock sensor by taking wrench and gently tapping it on the manifold and see if you note a timing change. 


Check out Your Vehicle’s Spark Plugs 

Did you know that you can tell how your engine is performing, based on the spark plugs? Believe it or not, spark plugs can tell a story of demise if they are looking fractured, yellowish in color or even blistered. So, look at your vehicle’s spark plugs and if there is a replacement that needs to happen, don’t hesitate to do the task. Spark plug replacement can save you lots of money and headache in the future! 


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