What Is A Rod Knock Regarding Engine Functionality?

Rod Knock

A rod knock is a low-pitched knocking sound which is heard low in the engine. It tends to increase in frequency as the engine continues to increase its speed. However, the sound can always be heard at any speed of the engine.

If you get to hear a knocking sound which disappears just after the engine is warmed up, that is not a rod knock. It might be something such as leaking exhaust gasket. If you think you have a rod knock, you should always consult an experienced mechanic.

A rod knock is very expensive to fix; hence, you have to be sure of what it is before driving in the head first.

More Details On The Rod Knock

Rod Knock

To begin with the basics, the rod is the section of the engine that connects the crankshaft to the piston. The area at which the rod is connected to the crankshaft, there is a noticeable bearing which part the rod from the crank journal. The bearing is created from a softer material than the crankshaft or the rod.

When the engine is designed, there are particular gap tolerances which are built into it, the crankshaft to rod bearing is no difference. Hence, the tolerance purpose is to allow a particular amount of oil through from a hole at the crankshaft journal as well as remain on the bearing surface. Oil films on the bearing and prevents the two parts from colliding while the engine is operating normally.

In case the tolerances get too big from deformation or wear, the oil films incorrectly and end up getting the rod knock. The noise that occurs due to the rod knock comes from the collision of the crankshaft journal and the bearing during the power stroke of the engine cycle.

Causes Of Rod Knock

If the collision of the crankshaft and the bearing worsens, it is likely that the rod has collided with the crankshaft journal and the bearing has become out of place. Rod knock mostly occurs when the bearing spins at the end of the rod and gets out of its position.

It normally happens when the rod cap stretch in the case of abusive driving situations. It can also be caused by lack of lubrication due to lack of oil or in case the oil flows incorrectly. The rod knock can also result due to the combination of the three causes.

What To Do In The Case Of A Rod Knock

Rod Knock

A rod knock is a critical problem regarding the engine. When the rod knock occurs, it means that the engine is not working properly. A rod knock is just the death knell of an engine! Once the rod knock happens, it cannot repair itself. The rod bearing should be replaced as well as fixing the associated parts.

Hence, you should not replace just one rod bearing since the whole engine will require complete rebuilt at that point or be replaced.

Since the rod knock is due to severe failure of the crankshaft connecting the rod bearings, the repairs need engine removal and disassembling at a particular expense. All these activities should be done by an experienced mechanic.

How to install rod bearings with engine still in the vehicle, watch video

How To Be Sure That A Rod Knock Is A Rod Knocking?

Rod Knock

If you want to test if your engine experiences a rod knock, the test is easy, just revive up the engine and carefully listen for a loud knock when the engine rotates. An experienced mechanic can recognize the sound with ease.

However, you should know that not every sound you hear from the engine is not a rod knock. Hence, an experienced mechanic is needed to recognize the sound.

A rod knock will always sound louder as the engine heats up. The sound will not seize as the engine becomes warm. If the sound stops, it is probably something different such as exhaust leak which shuts itself as the engine gets warm.

Rod Knock

A rod knock gets worse over time. If the sound is a light tap that stays the same, it may be cam noise, tappet or lifter.

The rod block cannot only be caused by a spun rod bearing but also a worn out bearing over time. If the bearing spins where it is connected, oil pressure will increase because of the less flow of oil.

Hence, as the bearing wears down quickly, the oil flow will increase due to large clearance and easy path for the oil to follow. The increasing pressure at first may not always be true, but you will see a great loss of oil pressure in short period. Loss of oil pressure depends on the type of engine as well as the amount of damage.

What Were You Doing At The Time Of The Start Of The Noise?

Rod Knock

In most cases, a spun bearing occurs because you were either doing something unreasonable with your old engine such as reviving the engine with two hundred thousand miles on it or you let it go dry of oil. These two reasons can spontaneously cause the bearing to spin.

Rod knocks are rare in engines with low mileage. Also, you have to look at the maintenance history of your engine. If the oil is changed after every three thousand miles with a brand-new filter, the rod knock is less likely to happen. New engines are expected to last long.


Rod Knock

There are many things to consider when suspecting the occurrence of a rod knock. However, there is only one way to finalize that your engine is experiencing the rod knock. Take your engine to the experts who can tear it down. If you continue driving the engine experiencing a rod knock, a catastrophic damage is likely to happen.

Hence, you should always be keen on the sound that comes from your car’s engine and in case you suspect something fishy, do not wait but take your car to an expert.

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