If you hear a knocking sound from the engine and it doesn’t go away when you accelerate or decelerate, then it is likely that you have a rod knock.
A rod knock is an internal combustion engine problem in which there is abnormal noise caused by broken or worn piston rods in one or more cylinders. The following are some signs to look out for if you think that your car might have a rod knock:
Table of contents
- Symptoms of Rod Knock
- Causes of Rod Knock
- How to Diagnose Rod Knock
- How to Fix a Rod Knock
Symptoms of Rod Knock
1. Abnormal Noise
Abnormal noise is the most common symptom of rod knock. It occurs when the cylinder walls are slightly damaged and can be heard with your ear pressed against the engine block.
You will hear a knocking sound, followed by an unusual silence. The sound is similar to that made by a door slamming shut or someone striking a piece of metal with a hammer.
It may also be characterized by popping noises and metallic rattling sounds, which come from broken crankshafts and pistons respectively.
It’s important to note that not all abnormal noises that emanate from an engine can be attributed to rod knock, there are many other causes for this phenomenon including worn valves or seals, faulty timing belts/chains/pulleys/shafts associated with internal combustion engines (ICEs) as well as excessive heat buildup caused by poor cooling systems.
2. Decrease in Engine Performance
If your engine is losing power, it may be suffering from a rod knock. A loss of power can also be accompanied by other symptoms such as decreased fuel economy and difficulty accelerating or maintaining speed on the highway.
This may be due to an engine that isn’t in its optimum operating range because of excessive wear and tear, an indication that your vehicle is running poorly and needs service soon.
3. Knocking Sound from The Cylinder Head
A knocking sound from the cylinder head is a symptom of rod knock. Rod knock is caused by one or more pistons striking their respective cylinder heads, which can be caused by worn or damaged engine parts.
If you notice this symptom while driving your car, you should find ways to do a thorough check-up as soon as possible to ensure that it doesn’t get worse and cause further damage to your vehicle’s engine.
4. Low Oil Pressure
In addition to low compression, low oil pressure can cause rod knock. The reason for this is that the oil’s main function is to keep the engine lubricated and cooled.
Oil pressure is measured in pounds per square inch (psi). A healthy engine has a psi range of 25-65. Anything below 20 can be indicative of some problem with internal components like your pistons or valves, while anything above 65 may suggest that the engine isn’t getting enough lubrication or cooling due to a leaky seal or gasket.
Causes of Rod Knock
1. Wearing or Damage to The Engine’s Internal Parts
If you hear a knocking sound that seems to be coming from inside your engine, it could be a rod knock. This type of piston noise is caused by wear on the pistons and/or connecting rods.
It can also happen when there are large pieces of debris floating around in your oil, which will cause worn parts to bang together inside your engine.
2. Broken or Loose Timing Chain Tensioner
If you suspect a broken or loose timing chain tensioner, it’s best to check for looseness first. If the tensioner is not in good condition and does not have enough tension on the timing chain, you may be able to perform a simple test and determine whether or not it needs replacing. A functioning tensioner should be able to protect against wear and tear by keeping everything in alignment over time.
3. Worn Water Pump Bearing
Water pump bearings are made of high chromium bearing steel, and as such, they can be damaged by water pump bearing wear. Water pump bearing wear can cause the water pump to fail, which can lead to an overheating engine. If they are worn, they can also be the cause of rod knock.
4. Worn-out Main Bearing
The main bearing is the bearing that supports the crankshaft. It’s a critical part of your engine, but it’s also very simple and inexpensive to replace. If it’s worn out or damaged in any way, it could lead to a rod knock problem.
5. Cracked or Broken Flex-plate or Flywheel
The flex-plate or flywheel is a metal disk that’s bolted to the engine, with teeth on its outer edge that engage with the crankshaft.
If you suspect your flex plate or flywheel has cracked or broken, you need to replace it right away. A broken flex plate or flywheel can cause serious damage to other parts of your engine.
6. Worn Alternator Rotor Bearings
Worn alternator rotor bearings can result in a rod knock. These rotor bearings are located on the back of the alternator and can be replaced by removing the alternator and replacing its bearings.
How to Diagnose Rod Knock
1. Check The State of The Oil Level
To check the state of the oil level, remove the dipstick and reinsert it. The mark on the dipstick should be between the two marks on the tube. If it’s below, add some fresh oil to bring it back up to a safe level. The exact amount of oil you’ll need will depend on your car’s age and condition.
2. Drain The Engine Oil
One of the steps to diagnosing engine knock is to drain the oil. Remove the oil filter and then remove the drain plug. Next, remove the oil pan and let all of the old oil drain completely into a suitable container.
Inspect this old engine oil for metal shavings. If you find any, it could indicate that your engine components have worn down so far that they’re actually starting to break apart (which would cause knocking).
Replace any filters that need replacing and clean off any residual dirt from your engine before putting in new fresh motor oil!
How to Fix a Rod Knock
1. Oil Change service
Remove the oil filter by using a wrench to loosen it. Clean the oil filter housing with an old rag or paper towel. Replace the filter and tighten it back into place. You may need to use a socket wrench or an adjustable wrench to do so, depending on your vehicle’s make and model.
Fill up your engine with fresh oil (ensure that you check your owner’s manual for the correct amount). If you don’t know how much new/clean oil you should add, consult a mechanic or visit an auto parts store for help.
Start up your car, run it for a few minutes, then shut it off again once more before checking whether there are any leaks from around where the filter was removed earlier in this process.
2. Remove The Crankcase and Inspect The Cod Rod Bearing
Check if there is any abnormal noise coming from the engine. If you hear a thumping or knocking sound, it’s likely that your car has experienced a rod knock.
Check all con rods (connecting rods) for signs of fatigue or wear in both ends—the cylinder end and the cap head end—and inspect them for cracks or other damage.
In addition to inspecting them visually, also remove each bolt securing one end of each con rod assembly; re-torque them as needed; consider inspecting their cod rod bearings; replace as necessary.
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3. Pour Fuel-injection Cleaner Into Your Gas Tank
This is a liquid that helps clean the engine and can be found at auto parts stores. Pour it in through the filler cap, which you open by turning it counterclockwise.
You’ll want to do this once every few months or so—but don’t worry too much about getting it exactly right! The timing for cleaning your car’s fuel system will vary depending on a number of factors, including how often you drive, where you live and work, and how old your vehicle is.
Keep in mind that not all rod knocks are serious, nor do they always indicate engine damage. In most cases, your engine will continue to run smoothly and you won’t need to do anything about it.
However, if you’re hearing a knock from your vehicle’s engine, it might be due to: wearing or damage to the engine’s internal parts, worn alternator rotor bearings, cracked or broken flex-plate or flywheel, worn out the main bearing, worn water pump bearing, or broken or loose timing chain tensioner. Follow the steps listed above to diagnose and fix them as soon as possible to prevent any further damage.
Ugo is a passionate car enthusiast with a Bachelor of Electrical and Electronics Engineering degree and hands-on experience in troubleshooting and fixing automobiles.
I combine my electrical and mechanical engineering knowledge with practical skills to address car-related issues.
My love for cars and dedication to educating others led to the creation of Fixandtroubleshoot.com!