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If you’re a car enthusiast or have ever owned a vehicle, you may have encountered some unusual noises from under the hood of certain cars. However, one of the most dreaded sounds is a persistent knocking noise that can indicate a severe engine problem known as rod knock. In this article, we will delve into what rod knock is, what causes it, and how you can fix it.

What is rod knock?

Harley Davidson Engine Connecting Rod stacked in a basket
Engine Connecting Rod | Scott Olson via Getty Images

Rod knock is a term used to describe a knocking or banging sound that occurs within the engine’s internal components. Specifically, it refers to a distinct noise that arises from the connecting rods responsible for connecting the pistons to the crankshaft. The knocking sound is caused by excessive play or “looseness” in the rod bearings, which are the components that allow the connecting rods to move smoothly on the crankshaft journal.

The main culprit behind knock is insufficient lubrication. Without proper lubrication, the rod bearings can wear down over time, leading to increased clearance between the connecting rod and the crankshaft. This clearance results in the knocking sound as the rod slaps against the crankshaft during engine operation.

What causes rod knock?

Several factors can contribute to insufficient lubrication and subsequent rod knock. One common cause is old or degraded engine oil. According to Valvoline, over time, engine oil breaks down and loses effectiveness, becoming less capable of providing adequate lubrication to the moving parts. Another factor is low oil levels, which can occur due to leaks, burning oil, or neglecting regular oil changes.

To fix rod knock, the first step is to identify the underlying cause. Start by checking the engine oil level and condition. If the oil level is low, add the appropriate amount recommended by the vehicle manufacturer. However, merely adding oil will not solve the problem if the oil is bad or the bearings have excessive wear. Once you hear a knock, the engine is close to causing catastrophic damage.

Can you fix rod knock?

A row of Piston and Connecting Rods in a machine shop
Piston and Connecting Rod | Bloomberg via Getty Images
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In most cases, repairing rod knock will require replacing the rod bearings. This task, however, is more complex and typically requires professional expertise. It involves disassembling a portion of the engine to access the connecting rods and bearings. Once the old bearings are out, new ones are put in the engine, ensuring proper clearances and improving engine performance.

In some instances, rod knock may indicate more severe engine damage, such as a bent connecting rod or crankshaft. These issues require thorough inspection and potentially more extensive repairs. Therefore, it’s essential to consult a qualified mechanic or automotive professional who can diagnose the problem accurately and recommend the appropriate course of action.

What should you do if you hear your engine knocking?

In conclusion, rod knock is a concerning problem arising from insufficient lubrication and excessive play in the rod bearings. It is crucial to address the issue promptly to prevent further engine damage. Start by checking the engine oil level and quality, and perform an oil change if necessary. If the knocking persists, answer the door by consulting a professional mechanic who can diagnose the problem accurately and recommend the appropriate repairs.