6 Symptoms of a Bent Connecting Rod in Your Engine
A defective connecting rod is one of the most disastrous forms of engine failure. This defect is commonly referred to as a “thrown connecting rod” or “thrown connecting rod”. When a connecting rod fails, it is very likely that the piston or connecting rod will crash through the engine block at very high speeds, damaging everything in its path.
What is a connecting rod?
The connecting rod is the connection between each piston and the crankshaft in an internal combustion engine. When the crankshaft rotates, the piston moves back and forth very quickly, putting a lot of pulling force on the connecting rod.
The connecting rod has bearings between the rod and the crankshaft. These bearings are lubricated and prevent metal from slamming against metal as the crankshaft rotates. Similarly, there is a pin that connects the piston to the top of the connecting rod. This pin is called the piston pin, piston pin, piston rod, etc. Main Symptoms of a Bent Connecting Rod
The driver will notice this because there are some very noticeable symptoms. Here are some of the most common symptoms that indicate a failing connecting rod:
1) Low Compression (Causes of Low Compression)
You might be able to run your car without any major issues even if your connecting rod is slightly bent. However, the cylinder with the bent rod will probably have lower compression than the other cylinders.
If you’re concerned that you might have a bent rod, consider running a compression test first. If the compression measurements vary by about 10% on all cylinders, your rod is probably fine.
Be aware that low compression can occur for a variety of reasons. If the compression test is unsatisfactory, a leak test should be performed to narrow down the possibilities.
2) Loss of Power
This symptom occurs in conjunction with a loss of compression. As already mentioned, the connecting rod “connects” the piston to the crankshaft and transfers the energy generated by the combustion process to the wheels of the vehicle.
If the rod is bent, it can cause the piston to move unevenly, resulting in a loss of compression in the cylinder. This can prevent the engine from producing the same power as normal, leading to a loss of power and acceleration.
3) Engine Knocking (Connecting Rod Knock) – Abnormal Noise
When the engine starts and runs, you may hear a “clattering” noise. It is a recurring knocking noise that gets louder as the engine speed increases. This is colloquially known as “connecting rod knock”. The noise may disappear after a short period of time as oil circulates and lubricates the engine components.
4) Low Oil Level or Oil Pressure
If the connecting rod is broken or failing, the engine may suddenly lose a large amount of oil, which can have a devastating effect on the engine’s oil pressure. Your engine may be fitted with an oil pressure gauge that will let you know when the oil pressure is too low. You will probably see a warning light on your dashboard.
5) Visibly Bent or Damaged Rod (Bent Connecting Rod)
If you suspect that your connecting rod is bent or damaged based on other symptoms that may be present, you should visually inspect the rod itself to confirm its condition. This requires disassembly of the engine, which should only be performed by an experienced mechanic.
6) Engine Stuck (Engine Smoke)
If a connecting rod is thrown off, the whole engine can stall and seize. You will know the engine is stuck because you will not be able to crank it by hand (using a wrench on the crankshaft belt bolt). You will have to turn it over by hand this way even if the engine will not start or start.
If you have ever thrown a connecting rod off, you will probably recognize it. When a connecting rod is thrown off, metal will fly out of the engine compartment, often accompanied by a loud bang. After this happens, you may notice a large puddle of oil under your car or a large hole in the block.
Causes of Connecting Rod Failure
There are several possible factors that can cause your engine’s connecting rod to bend. Understanding the underlying issue can help you avoid future problems.
1) Flooded Engine (damaged pistons)
Unlike air, liquids are not really compressible. If your engine is hydrolocked (i.e. filled with fluid rather than just air), there is a risk of bending the connecting rod when starting the vehicle. You will need to drain the engine before you can start the car normally.
2) Pre-ignition or detonation (low octane fuel)
Pre-ignition and detonation are terms used to describe the abnormal combustion of the mixture in the combustion chamber. Massive pre-ignition or detonation can cause large cylinder pressures, sometimes beyond what the engine is designed for. Such greatly exceeding expected cylinder pressures can cause catastrophic engine failure.
3) Poor Engine Management (ECU)
If you are using aftermarket engine parts, your ECU may have been programmed by a tuner. If this tuning is too aggressive for your operating conditions, or pushes the engine a little too hard, you may end up with a connecting rod spinning.
Intake, exhaust, boost pressure regulators, or larger turbos.
4) Over-revving the engine (check engine light)
As the engine revs higher, the pistons move faster, which increases the force on the connecting rod.
Most engines prevent over-revving at or just below top speed, reducing fuel consumption. The easiest way to rev an engine is with a manual transmission.
5) Low Oil Pressure
Loss of oil pressure can occur for a number of reasons, including engine leaks, using the wrong viscosity oil, and problems with the oil pump.
Low engine oil pressure can negatively affect the lubrication of internal components and put additional stress on connecting rods. This lack of lubrication can cause friction, heat buildup, and ultimately bend connecting rods.
6) Engine Modifications (Turbo Engine Limp Home Mode)
Many factory connecting rods are thinner than those on older vehicles. This is done for efficiency and cost-saving reasons. Thinner connecting rods are fine for stock power, but if you want to make more power, the stock connecting rods are not always sufficient.
If you want to make your car faster, do some thorough research on forums related to your specific car to find a general blueprint for the performance level you are trying to achieve.
Assessing the Damage
Here are two common diagnostic tests you or a mechanic can run to determine the extent of the problem: Compression Test
A compression test is useful as a first step in diagnosing a bent connecting rod. This test measures the pressure that develops within each cylinder of the engine while cranking. To perform a compression test, you will need a compression tester. How to proceed:
1) Warm up your engine.
2) Turn off your engine, and remove all spark plugs.
3) Install the compression tester into one of the spark plug holes.
4) Crank the engine for a few seconds.
5) Record the compression reading.
6) Repeat steps 3-5 for each cylinder.
If there is a noticeable difference in compression measurements between the cylinders, there may be a problem with the connecting rod of one of the affected cylinders.
Leak Test
This procedure requires a leak tester. To perform a leak test:
1) Set the engine at top dead center on the compression stroke of the cylinder to be tested.
2) Attach the leak tester hose to the spark plug hole.
3) Apply regulated air pressure (usually around 100 PSI) to the tester hose.
4) Record the pressure drop on the leak tester gauge.
A high percentage of air leaks may indicate a bent connecting rod causing a poor seal in the affected cylinder.
