rod bearing rod knock

Rod knock – Causes, Information, and Fixes

In Engine by Magnus Sellén2 Comments

rod bearing rod knockIt is vital that you listen to your engine noise occasionally.

The internal combustion engine is a complex mechanism where an air/fuel mixture is ignited hence moving the pistons. The pistons are connected to the crankshaft, which in turn turns the car wheels. If you hear a knocking sound coming from under the hood and it sounds like someone is hitting your car with a large hammer, then you could be suffering from rod knock.

You can confirm this by revving up the engine – the sound gets louder. Some people refer to the problem as spark knock, engine knock or engine pinging.

What causes rod knock?

rod bearingsTo understand what causes engine knock you need some basic knowledge on the relationship between the pistons and the crankshaft. The piston moves up and down due to the ignition of the air/fuel mixture by the spark plugs. A connection rod is used to join the piston head to the crankshaft. At the bottom side of the crankshaft are bearings that facilitate movement of the rod and crankshaft. To keep all moving components of the engine from overheating due to friction, oil lubrication is used.

The rod knock happens when the bearings wear out, and this causes the metal parts to collide with each other. When this happens, you will hear a knocking sound. The sound increases when you rev up the car. They could also collide due to diminishing engine oil levels leading to loss of lubrication.

The rod knock is similar to the piston slap that occurs when the wrist pin wear’s out and starts wobbling around the cylinders.

You should never ignore the rod knock as the problem becomes worse as you continue driving. As the bearings continue wearing out due to friction, they get worse and eventually they will break away from the crankshaft, blowing out your engine.

Video of the sound of rod knock:

 

How to fix it

If you hear rod knock inside of your engine, you have to replace the rod bearings. Damaged rod bearings does most of the times also damage the crankshaft and the rods. You may need some help to measure the crankshaft and the rods before replacing the bearings to make sure they are not too damaged.

The main reason you have a rod knock is that the rod bearings wearing out. Oil is used for lubrication of any movable engine parts. Oil leakages can be caused by a cracked head gasket or faulty oil pump. If you do not have sufficient lubrication of the moving parts, you will have more friction between parts leading to overheating of the engine.

You should stop driving your car the moment your car starts producing the knocking sound. Lack of immediate maintenance will result in further damage to the pistons, rods, and crankshaft.

How to identify rod knock?

Rod knock is identified by a repetitive rattling, knocking sound coming from the engine. The noise becomes pronounced the higher the rpm. If it only happens when you start the car then it could be a problem with the main bearing rather than the rod bearings.

Depending on the damage caused to the car the mechanical costs can be substantial. If further damage has occurred to the engine you will be forced to buy a new one. You will need some mechanical ramps, oil pan, oil filter wrench, and new oil filter to fix rod knock problems.

  • You will need the assistance of your mechanic to identify the extent on the damages. If the rod knock is as a result of low oil levels the following steps can be used for the oil change.
  • First, drive the car to the mechanical ramps. This should elevate the engine to a position suitable for repairs. Ensure that the hand brake is on.
  • Place the oil pan underneath the oil drain valve and remove the oil plug. This will drain engine oil to the oil pan. Ensure that all the oil in the car has properly being drained. Replace the oil plug.
  • Remove the oil pan and check your rod bearings for wear and tear. This may required some skills and use of a mechanic workshop manual. Let your mechanic do it for you if you are not sure of how to do it.

Some vehicles have carburetors and you need to clean it to prevent the accumulation of dirt and other foreign particles. Grime in the engine is a major cause for rod knock. If you do not fix rod knock the moment you start hearing engine noises you may find yourself replacing the whole engine. rod knock affects critical engine components like the rods, crankshaft, and pistons.

The biggest problem is when multiple bearings fail all at once. When the bearings have completely worn out you will have the rod grinding to the crankshaft.

Conclusion

Rod knock is caused by the rod bearings getting worn out or when you have low oil pressure. There are several moving parts in the engine and they all need engine oil to remain lubricated. When experience oil leakages these movable parts will grind against each other causing excessive heating due to the friction.

You identify rod knock from other engine noises by the fact that it increases the moment you rev up the car. The first thing you will need to do to fix rod knock is to replace existing engine oil. This is a simple do-it-yourself procedure that requires you to drive your car to a mechanical ramp.

Change the oil filter and pour in some new engine oil. The noise should subsidize. However, if you notice that the noise keeps getting worse even after the oil change it could mean that your bearings are damaged beyond repair. there could also be the existence of further engine damage.

In the instance, you will be forced to call your mechanic for further repairs or in the worst case scenario be forced to purchase a new engine. Rod knock is a serious engine problem that needs urgent attention the moment it occurs.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

Comments
  1. Is it best once the oil has been changed before even taking a part to see if it is actually the bearings that are beyond repair to let the oil sit and start occasionally? I’m trying to avoid taking the motor apart just to see the how the bearings are. However, I’m the beginning the knocking subsidies until it does get into the high RPMs then it gets louder and more prominent.

  2. I think I ran a bearing I heard that strange sound and my motor just turned off while driving is it a bearing because my oil light also went on

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