5 Symptoms Of A Bent Connecting Rod (& Replacement Cost)

Engine failure is something that no one likes to have to deal with, particularly if the connecting rod has bent. This condition is also known as “throwing a rod,” or simply just a “thrown rod,” but what does it mean?

This article examines the function of the connecting rods in the engine. Also, we discuss what symptoms to look out for when your connecting rods stop working and which causes it. Let’s begin with the signs to look for.

Low engine compression is the most obvious sign of a bent connector rod. This can lead to misfires and a check engine lamp on your dashboard. You may also hear loud engine sounds or have your engine seized.

Here’s a more detailed list of the most common symptoms of a bent connecting rod:

Bent Connecting Rod Symptoms

1. Low Engine Compression

The slight bend in the connecting rod could initially not cause symptoms. It will eventually cause a loss of compression within the cylinder if it continues to bend. 

A compression test is required to determine whether a bent rod was the problem. If the compression test shows that the cylinders are all within 10% of one another, there probably isn’t anything wrong with the rods. You will have to proceed with the leak test in order to confirm your diagnosis. 

2. Rod Knocking

The term “rod knock” is enough to get you shaking in your boots, and it should. A knocking sound coming from your engine's motor while it is running could indicate a problem with one or more connecting rods. The engine's load will cause this sound to become more frequent. 

It is possible for the sound to disappear within a few minutes. The oil that circulates through the engine and causes more lubrication can cause this noise to disappear. If the bearing or connecting rod is the problem, the sound may not be heard. 

RELATED: Rod Knock: – Causes, Symptoms & Repair Cost

3. Broken or bent rod

Unless you are physically inspecting the engine, this isn’t the easiest defect to notice. The engine must be disassembled to inspect the rods visually.

If the engine is in a repair, or is going to be rebuilt, the mechanic will need to inspect the connections rods. It is easier to repair a bent rod if the engine is apart than it is to fix a problem.

4. Low Oil Pressure

If the connecting rod breaks or becomes defective, your engine will quickly lose oil. Oil pressure can change as a result. The oil gauge on your dashboard will indicate the drop in pressure. A warning light may be lit if the pressure drops. 

Low oil pressure should not be used to drive your vehicle. Low oil pressure can lead to a motor that is too hot, leading to additional repairs. 

RELATED: 4 Symptoms of Low Oil Pressure, Causes & How to check the oil pressure

5. Seized Engine

Engines can become stuck or stalled by throwing rods. It’s not hard to know when the engine has seized because you won’t be able to turn it over by hand with a wrench on the crankshaft pulley bolt. In normal situations, you would be able to turn the engine by hand if it isn’t starting. 

Also, thrown rods can make a loud banging sound or metal flying out of the engine. The defect could lead to an enormous hole in your engine block or a large puddle beneath the vehicle. 

The Causes of Connecting Rod Failure

Over-revving and detonation are two of the leading causes for a bent connector rod. You should be aware that deep water could have caused your engine to flood, which can lead to hydrolock. This will cause your connecting rods and other parts of your vehicle to bend easily.

Here’s a more detailed list of the causes of a bent connecting rod:

1. Flooded Engine

Fluid is not compressible but air is. A hydrolock is when an engine becomes clogged with fluid rather than air. 

Hydro-locking can cause a bent connecting rod when the engine starts. To ensure this doesn’t happen, you must remove the water from the engine before you turn it on. 

2. Pre-ignition and Detonation

Each of these terms indicates that combustion has been disrupted. To ensure reliable performance, the mixture of air and fuel must ignite at certain intervals.

However, there are several factors that can lead to detonation and pre-ignition. These include using lower-octane fuel ratings, carbon buildup, and advanced ignition timing. These events can lead to abnormal cylinder pressures, which could cause rods to break or bend. 

Related: 6 Reasons Your Car's Engine is Knocking Or Pinging

3. More Revving

The pistons are faster so more power is applied to the connecting rods when the engine revs up. A replacement could be necessary if you crank your engine up beyond what is required.

Modern engines include safety features to stop over-revving. Fuel might be reduced to stop damage if you exceed the redline. 

In many cases, this damage occurs with manual transmission vehicles that don’t have fail-safes. When you downshift into a gear that’s too low, you might force the RPMs to rise too high, leading to catastrophic failure. 

4. Modifications

You might have to tune your engine if you add engine optimizers or any other part to your car. You could cause the engine to fail by pushing it beyond its limit, and possibly even throw off.

You should also take extra precautions when installing a turbo, intake or boost controller. You must account for this new hardware and properly tune the engine if you don’t want to damage the connecting rods. 

Locate the Connecting Rod

An integral component of an internal combustion engine is the connecting rod. The connecting rod is attached to the crankshaft by a bearing.

Bolted to the end is a connecting rod bearing cap. Connecting rods can be hollowed from many materials including high-grade aluminum and micro-alloyed, as well as sintered or titanium, and CFRP.

The Function

It is responsible for connecting the crankshaft to piston, where it transmits power. These rods convert linear up and down motion from the piston into the circular movement of the car’s crankshaft. 

Bearings are located between the crankshaft rod and connecting rod. The bearings protect metal against metal and maintain proper lubrication during crankshaft rotation. 

A pin also connects the top of connecting rod to piston. The pin also goes by many other names, such as the wrist pin, piston pin, or gudgeon. 

Connecting rods are subject to a lot stress and tension. This can lead to greater weakness. If it becomes weak, it won’t be able to handle the pressure from combustion and could break or bend. The damaged connecting rod can cause engine failure by causing problems with power strokes as well as compression strokes. 

Repair of Connecting Rods

For parts and labor, a replacement of a bent connector rod can cost up to $3,000 Some vehicles will need a total engine overhaul, particularly if the connecting rod is thrown. Repairs for luxury vehicles and large models may cost up to $5,000.