What is Rod Knock? – Causes, symptoms (and repair cost)
When your car is idling, you may start to hear a scary engine noise known as knocking. It often presents as a loud bang, loud enough to stop your heart when considering expensive engine repairs. However, not all motor shots are rod shots.
So what is rod rattle, what causes it, and how can you identify the symptoms of this engine problem?
What is Rod Knock?
A rod knock is a deep knocking sound that comes from the engine. It is caused by worn or damaged connecting rod bearings. The vehicle’s connecting rod bearings have excessive play, causing additional movement. As the piston changes direction, metal begins to collide with metal, producing the knocking noise.
This noise will increase as the load and speed increase.
What is Rod Knock like?
You can easily notice the stem knock if you’ve heard it before. These are often loud knocks coming from your engine as you rev it and release the gas. Most of the time you hear it directly after releasing the gas.
Here’s a video of what it sounds like:
Causes of rod knock
The most common cause of connecting rod knock is the wear of the connecting rod bearings. Rod knock is only caused by one thing, but several other causes can cause symptoms similar to rod knock.
Here are some of the things that could cause stem bumps or stem bump-like symptoms:
1. Worn bearings
The only cause of rod rattling is bearing wear. As the pistons move up and down in your car’s engine, they rotate the crankshaft, which is responsible for sending power to the wheels. The bearings are responsible for ensuring that the movement of the piston remains smooth and controlled.
However, these bearings wear out over time and can slip out of position. As the bearings wear, the piston rods begin to rattle against the crankshaft, creating a unique knocking sound.
The only way to fix this is to replace the bearings, which are deep in the motor.
2. Low octane
An explosion may sound like a stab. If the engine is running as it should, the air-fuel mixture is burned in a single detonation in each cylinder. However, detonation knock occurs when this mixture explodes in several places at once, producing a knocking sound.
One of the causes of this detonation is an octane rating that is too low for the engine. If you have a high-performance engine, you need a higher octane rating than most cars. A high octane number burns evenly, avoiding that ping.
This problem has an easy solution, as it simply forces you to use higher-octane fuel the next time you fill up the car.
RELATED: 6 Causes of a Knocking or Knocking Car Engine
3. Bad timing
Another reason for detonation is poor engine timing. Timing refers to when the spark plugs fire. This synchronization is controlled by the computer.
When the timing is off, the spark does not fire when it should, resulting in multiple cylinder knocks. This is what causes the detonation. To solve this problem, the moment must be fixed.
4. Lean air/fuel mixture
Another reason for detonation is having a lean air/fuel mixture. This problem can be caused by faulty oxygen sensors, faulty fuel injectors, a faulty fuel pump, or a faulty mass air flow sensor.
Lean combustion occurs when there is not enough fuel and too much air. Without the correct amount of fuel, the mixture cannot burn fast enough, causing multiple detonations.
5. Defective motion sensor
Another reason for the detonation knock is a faulty knock sensor. Fortunately, this doesn’t happen too often in newer cars, as the computer controls the air/fuel ratio, timing, and fuel injectors.
The knock sensor detects any situation causing the noise and alerts the ECU, where corrective action can be taken immediately. So if the car has a faulty knock sensor, the computer won’t know how to correct the problem and could allow the engine to knock.
6. Defective belt tensioners/pulleys
The last reason you may hear the engine knocking is because of something that is not coming from the engine at all. When the accessory belt is not at the correct tension, it can generate a similar noise.
When the engine turns, the belt turns. It is connected to many pulleys in the engine compartment and needs to be pulled to make it run quietly and smoothly. If the belt becomes loose, the tensioner is not working properly. However, you can also have problems if one of the pulleys rotates.
This condition results in rattling and pinging noises that could be mistaken for engine knock. To solve this problem, you only need to replace the belt, tensioner, or pulley.
Symptoms of rod knock
If the vehicle actually has a worn rod bearing and is not knocking for one of the other reasons, there will be two common symptoms.
1. Keypress sounds
Obviously, the main symptom of a rod knock is a knocking noise. You will probably hear this loud clicking sound when you first start the car.
It will also increase as you increase the load on your vehicle or step on the accelerator.
2. Low oil pressure
When a bearing fails or begins to fail, you may notice lower-than-normal oil pressure. This is most obvious when the vehicle is first started.
The Check Engine Oil light may even come on on your dashboard, notifying you of the pressure. If the light goes off and the pressure returns to normal after a few minutes, this is a strong indication that a bearing is defective.
Stab Repair Cost
The cost to repair the stab wound will be $2,500 or more. On some vehicles, such as a Subaru Forester, connecting rod repairs can easily cost $5,000 or more with parts and labor.
Replacing connecting rod bearings is not an easy task. First, the defective part is located deep in the engine. You will need the connecting rod bearings, but also the head bolts, engine gaskets, and new gaskets. Additionally, the engine and cooler lines should be flushed. In some situations, you will also need new connecting rods, pistons, timing chains, crankshafts, and camshaft bearings. With all those extra parts involved, it might be best to consider an engine replacement instead.
