Bent Connecting Rod Symptoms – How To Diagnose A Bent Rod?

Bent Connecting Rod Symptoms – How To Diagnose A Bent Rod?

August 11, 2021 0 By CarGuy

So, you have been experiencing some loss of power and you started to hear some metallic sounds that are coming from your engine? I’m not trying to sound negative, but when you are experiencing some metallic sounds from the engine, it means that something is really wrong and some metal is rubbing when it shouldn’t. All these are bent connecting rod symptoms.

Any metallic sounds that come from the engine should be a red alarm for you. When you hear some metallic noises, it means that something is going down very soon.

In these cases, the best option is to stop the car and do not drive it. Because if you drive the car, you could only make things much worse than they are.

When there is some metal rubbing, the damage gets bigger and bigger with every minute that the engine is running. And the only solution to fix this issue is by tearing apart the engine. In order to see if there is something that can be done to save this engine.

In this article, we are going to learn a lot about connecting rods and their role. We also going to go through all of the bent rod symptoms and the possible outcomes in solving this problem. Then we are going to explain how much is a bend rod replacement costs. So, if you want to learn more about bent connecting rod symptoms. Follow along.

What Are Connecting Rods?

A connecting rod is an essential part of every internal combustion engine. The connecting rod is the part that is connecting the crankshaft with the piston.

The connecting rod’s task is to convert the reciprocating motion into the rotation of the crankshaft. Basically, the piston is transmitting the energy from the combustion process and the rod is converting that energy into a rotational force that spins the crankshaft.

It may sound complicated, but in reality, it is very easy to understand. If you look online for some animations of how an internal combustion engine works. You will notice how the piston moves up and down. When it goes down it transmits the energy from the explosion into the crankshaft.

Anyway, these connecting rods are prone to fatigue. And this fatigue is developing with the years of work and the stress that is applied to the piston. Even though they are built from special materials and they have unique design that can withstand the energy. Sooner or later, they fail, and when they fail, catastrophic engine damage happens.

Sometimes it is repairable, but sometimes these rods can scrap an engine. Especially if they fail at high-speed pulls when the engine is working at high rpm’s.

Before they catastrophically fail, they tend to develop some symptoms. And these bent connecting rod symptoms we are going to cover in the next chapter.

Bent Connecting Rod Symptoms

As we said, when a connecting rod is failing it is developing some symptoms that can be recognized and a protentional catastrophic engine failure can be prevented. It depends on you and your good ears to diagnose the issue. In this chapter, we are going to cover all of the bent connecting rod symptoms that you have to know in order to diagnose this issue with a bent connecting rod. So, let’s begin.

  1. Bad Engine Performance
  2. Rod Knock Sound
  3. Cylinder Wall Rubbing Sound
  4. Oil Ring Failure
  5. Bad Engine Compression
  6. Low Oil Pressure
  7. Low Oil

1. Bad Engine Performance

A bad engine performance is probably one of the first bent connecting rod symptoms that you are going to feel on your car.

When a rod is bent, nothing works as it should have. There is a lot of play and weird sounds coming from the engine. Resulting in power loss and poor engine work.

The compression will be low and your engine will hardly be able to keep running. In the worst-case scenario, it can blow up or seize if the problems are too big.

One of the first sounds that will remind you of this is the rod knock sound. And we are going to cover that in the next chapter.

2. Rod Knock Sound

One of the first bent connecting rod symptoms is probably the rod knock symptom. This rod knock is caused because the crankshaft bearings are pretty much done.

These bearings are known to wear off if there are rare oil changes. As they wear and they lose of their material. A small play develops between the rods and the crankshaft.

This play between the rods and the crankshaft develops that famous rod knock sound that we all hate. When a rod is knocking you know what’s going on.

If you hear a rod knock sound this is the first symptom that should alarm you. If you repair this problem on time, you will only get away with some machining work on your crankshaft and you will be good to go.

But if you delay this, the rod that is knocking will start to bend. And this bend will scar your cylinder walls and total your whole block.

Instead of paying $500 for simple machining work, you are going to pay thousands to swap the engine.

So, when you hear a rod knock, don’t wait and make sure that you repair the engine on time.

3. Cylinder Wall Rubbing Sound

One of the bent connecting rod symptoms is the cylinder wall rubbing sound. This sound is accompanied by the rod knock. And this sound will develop if you are running your engine too long with a rod knock.

The rod knock will sooner or later ruin the balance of the work of your piston and the piston will start to hit the cylinder walls. Rubbing with them and creating scars on the cylinder walls.

These grooves can get deeper and deeper as time progresses. And if you apply a big load on the engine, the rod is going to break sooner or later resulting in a hole in the cylinder wall.

Bent Connecting Rod Symptoms

A damaged piston, caused by a bad connecting rod. Free Stock Image By Pixabay

A hole in the cylinder wall unfortunately is not something that can be repaired. Also, if the scars are too large in the cylinder wall it can cause the engine to be scrapped.

Scrapping the engine will result in getting a new engine and big repair bills. Even though some shops are installing sleeves inside of cracked blocks. But this doesn’t work very often and your engine will sooner or later is going to start losing compression and you will have to get another engine.

So, the best thing to do is to repair the engine when it starts knocking if you want to be safe.

4. Oil Ring Failure

Oil rings can fail also if the piston is unbalanced by the worn bearings. The worn bearings will cause the piston to move around in the cylinder and damage the cylinder walls.

All this uneven work will also damage the piston rings. These piston rings are designed to maintain the compression and prevent the oil to come into the combustion chamber.

And if they are not doing their job anymore the engine will start to lose power and you will feel how the engine runs very poorly.

This poor work is a result of the low compression. In this case, the best thing is to open up the engine and see what’s going on inside. Make sure that the cylinder walls are good and replace the damaged bearings and piston rings.

This can also be pricey since it requires a lot of man hours to do this job properly.

5. Bad Engine Compression

Another in the list of bent connecting rod symptoms is low engine compression. Low compression is caused when the oil rings are not sealing and the oil is getting inside of the cylinders.

Since the cylinders need a vacuum in order to function properly. When you have a bent rod, the O-rings do not seal and there is a loss of compression. The bigger the leak the bigger the compression loss.

This can greatly affect your performance and also cause more damage to the engine block and crankshaft.

In order to see if you have good compression on your engine. You need to do a compression test. We recently wrote an extensive article about doing a compression test DIY. So, if you want you can check it out.

6. Low Oil Pressure

Low oil pressure is also a bent connecting rod symptom. As we said. The O-rings are the first that fails when there is a rod knock caused by a bent rod.

Since the O-rings fail, a loss of oil and low compression occurs. The engine just can’t build up enough oil pressure to keep the other components inside of the engine lubed.

This low oil pressure can damage other pistons and rods in the process. Since they don’t have enough oil to keep them running well. Friction among the parts will appear.

The first parts that are going to suffer will be the rod bearings on the other pistons and more pistons will start knocking.

The end result of this will be a total compression loss or catastrophic engine failure. Since the whole piston assembly will be out of balance and the pistons will start to crack the cylinder walls and one of them is probably going to escape from somewhere creating a massive hole in the process.

And you don’t want that. That can happen if you don’t address this issue on time and you keep delaying a visit to the mechanic’s shop.

7. Low Oil

Low oil is also another bent connecting rod symptom. Oil gets low in these engines because they are burning it. The oil escapes from the O-rings and ends up in the combustion chamber and burns inside of it.

Some engines spend a certain amount of oil like 1L at every 1000 miles. But everything above that is unacceptable and this engine has to be opened in order for the O-rings to be sealing and inspect the rod bearings for possible damage.

If the rod bearings have damage on them then you will have to replace them. This is a good job if you want to do preventive maintenance. By replacing these parts, you will prevent so many issues and bent rod symptoms to appear in the first place.

If you noticed that your car is burning oil before the rods start to knock you are good to go. By replacing the rod bearings and O-rings you are going to make your life easier, to be honest.

What Causes A Bent Connecting Rod?

This is a good question. A bent connecting rod can be caused by multiple reasons and multiple factors. And we are going to cover them in this chapter.

  1. Engine Overload
  2. Bad Rod Bearings
  3. Overdue Oil Changes

1. Engine Overload

The number one reason is engine overloading. This can happen on a lot of performance engines that people are pushing them to the breaking point.

Revving an engine to high RPMs can have a damaging effect on it. This will basically put a lot of stress on these parts. The rods are taking the hardest load when you are running an engine to its limit.

The pistons are moving so fast that you cannot imagine. Some engines are revving up to 9000 rpm. And imagine what this is doing to your rods?

This amount of stress will probably gonna cause your engine to destroy itself if you are running it on so high speed for so much time. If a rod bends in this situation, is actually good, but in most cases, these rods are breaking and are creating a big hole in the engine block.

So, when you are planning to run mods on your car or you plan to create a track monster. The best thing to do is to replace your factory rods and pistons with high-performance parts. These high-performance rods are created to withstand a lot more torture than your factory rods and keep your engine safe in the process.

2. Bad Rod Bearings

Bad rod bearings can damage and bend your connecting rods. This is the case because the material from which these rod bearings are made is starting to wear off too quickly.

And if you don’t notice this wear, your rod bearings will basically disintegrate and make bend your rods.

If the rods are bent, you can also expect some more damage to the cylinder walls. The cylinder walls will get all mangled up and scratched.

This will result in scrapping your block altogether. So, if you are having an engine that is known for this issue and eats through rod bearings pretty quickly. Then it’s a good idea to replace them to be on the safe side.

This will make you sure that your engine is not going to give up on you and you will going to enjoy your engine for a long time.

Also, replacing your rod bearings is a good thing to do if you are having a higher mileage engine. Every higher mileage engine needs a small refresh at some point.

And replacing the rod bearings and O-rings will make you sure that this engine is going to live for many more miles into the future.

This job is a bit on the expensive side and you can expect to pay more than $700 for a good refresh. But at the end of the day is worth it. No more bent connecting rod symptoms for you.

3. Overdue Oil Changes

Rare oil changes can damage your engine and reduce its life by a big margin and also cause bent connecting rod symptoms.

This is the case because the oil is losing its ability to lubricate at 5,000 – 7,000 miles. It’s just doesn’t work as it used to and your engine is not lubed properly anymore.

This will damage the rod bearings and O-rings. Two overdue oil changes can ruin your engine. The rod bearings will give up and all sorts of issues will start to appear on your engine.

In order to prevent this damage to your engine, you need to replace your engine oil on time and you can be sure that you will drive your car for many more miles.

Also, it is a good idea to use high-quality engine oil. High-quality engine oil will make sure that your engine will work properly and you will not have to worry about your rod bearings and O-rings to develop issues.

And not to forget to use factory recommended oil spec. Remember that these engines were designed to run with this oil in mind.

Bent Connecting Rod F.A.Q

In this final chapter, we are going to answer a couple of frequently asked questions when it comes to bent connecting rod issues and symptoms.

Can A Bent Rod Be Fixed?

Yes, it can be fixed. But it much depends on the extent of the damage that your engine has. If the cylinder walls are scarred and your engine produces a lot of blowby a simple rod bearing replacement and a new rod may not fix the issue.

You will probably going to need some machining work in order to bring your engine back to life.

Bent Engine Rod Repair

The repair for a bent engine rod is pretty extensive and will require replacing numerous parts and machining work to get all the things right and the engine to function properly.

The first thing to do is to disassemble the whole engine in pieces and the damage has to be inspected. This will require washing the block in degreaser and see the condition of the cylinders if they can be bored and how much material can be removed out of them.

If they require too much boring the engine can be scrapped altogether or it will require the install of cylinder sleeves that will replace the factory cylinder.

The crankshaft also has to be machined and everything has to be smoothened out.

This job is labor-intensive and also time-consuming. So, if you want to rebuild an engine that has a big extent of damage it can cost you a few grand to do so.

How Much Does It Cost To Fix A Bent Connecting Rod?

As we said before, the repair cost depends on the extent of damage that your engine has. If the cylinder walls are scarred you will have to do machining work in order to bring the engine back to life.

The best-case scenario will involve a little bit of machining on the crankshaft and new rod bearings and O-rings. This job can be done for less than $1000. But if your engine has extensive damage, it can cost you a lot of money to be brought in life.

Because the block has to be machined, all the piston rings and bearings replaced. The crankshaft needs to be machined. This is too much work. So, if your engine is not holding some sentimental value then the best thing to do is to go for a new engine.

How To Prevent Bent Connecting Rod Problem To Appear?

In order to prevent problems and bent connecting rod symptoms to appear. The best thing to do is to do your service on time. And by this, I mean you have to change your oil at regular intervals.

Don’t delay the oil changes. The more you delay the oil changes the more the engine is suffering and the rod bearings and O-rings wear off.

This can cause rod knock and all sorts of issues. Also, don’t overload your engine. When you overload your engine you put a lot of stress on it, and when there is a lot of stress, rods tend to bend or break.

Can I Drive My Car Like This?

You can drive your car like this, but the extent of the damage that is done to the engine block and the crankshaft will be bigger and bigger.

This will result in scrapping the engine completely. So, if you are prepared for these consequences and you plan to replace the engine with a new one then you don’t have to worry about anything.

Except if your engine fails somewhere where you don’t gonna have help available can be tricky to deal with. So, the best thing is to address the problem as soon as possible.


In this article, we have covered a lot when it comes to bent connecting rods and bent connecting rod symptoms.

We learned which are all of these symptoms that happen when your engine rod gets bent. And these were the rod knock sound, the cylinder wall rubbing, low compression, low oil pressure, and more.

We also pointed out the reasons why these connecting rod symptoms start to appear, and these were the engine overload and also the overdue oil changes.

So, if you want to preserve your engine. Make sure that you are doing your oil changes regularly. If you are following this practice, you shouldn’t have to worry that your engine will develop a rod knock in the near future. And if you are dealing with a rod knock. The best thing is to address the problem as soon as possible.

We have covered the engine issues very extensively, so if you want you can check out our articles about metal shavings in oil. We also covered valve related issues, so if you face a problem like bad engine valves you can learn more by checking out our article on bad engine valves. You can also check our article on white sludge on oil cap if you are experiencing a similar issue. Thanks for reading.