What is rod knock? Symptoms, Causes, Diagnosis, and How to Fix

Engine problems and repairs are one experience most folks don’t want to experience. Would you? When a driver starts experiencing complications with the vehicle engine, they move towards trading or selling off the vehicle, thinking it is an expensive repair. Luckily, there are a lot of engine problems that are easier to fix than others.

A rod knock is one of these engine issues that might make you move towards trading or selling off your baby ride.

This article will unveil what rod knock is, symptoms of a rod knock, diagnosis, and how to fix it. We’ll explain in detail what you need to know and how to prevent rod knocks. Before we dive deep into all these, what is rod knock?

What is rod knock

rod knock repair cost

Rod knock simply means a noise or sound of one or more connecting rods hitting or rubbing against the crankshaft as it rotates in the cylinder bores. The connecting rods are connected to pistons and crankshaft. And, between the con rod and the crankshaft, there is a bushing (mainly known as bearing) made up of soft metal than the crankshaft and the con rod.

By default, car engines are manufactured with clearance tolerance for the bushing to fit in the crankcase journal.  The small clearance allows the engine oil to flow on the metal surface, preventing premature wear and tear. However, over time, the metal bushing between the con rod and the crank will start wearing off, resulting in rod knock.

In any case, rod knocks are not usually caused by normal wear because it takes hundreds of thousands of miles for the bushing to wear off. Majorly, rod knocks are caused due to premature wear. What could cause premature wear? It is usually caused by dirty motor oil, low oil level, low oil pressure, engine overheating, amongst others.

What is spun bearing?

Spun bearing refers to the outcome of unfortunate circumstances in the engine cylinder bores. What do I mean? Spun bearing is the result you get when there is a lack of lubrication in the engine, and the crankshaft rotates with the bearing instead of turning inside the bearing.

This is usually caused by connecting rods or nuts stretching due to improper bolt torturing during an engine rebuild. Several other factors, such as lack of lubrication, excessive heat, and high operating loads, can cause the bearing to wear. There are several other factors that can cause a spun bearing.

Symptoms of rod knock

rod knock symptoms

Like every other system component in your vehicle, there are few symptoms that tell when you have a rod knock. These symptoms are as follows;

Knocking sounds: The most common rod knock symptom is knocking sound. With a rod knock in place, you will hear a banging or knocking sound (as if someone is hitting metal on your iron door) when you turn on your car. The noise will increase as you step on the gas pedal.

Low oil pressure: When engine components like crankshaft, camshaft, and bearings start wearing out, the engine oil pressure will reduce. This is more noticeable when you first start up the car.

In some cases, it will trigger the check engine light and the oil light to display on your instrument cluster, indicating there’s an issue with the oil pressure. If these lights go off after a few minutes of idling or running the car and pressure returns, it indicates a rod knock.

What causes rod knock

Rod knocks are usually caused by one thing – wears or damages to the engine’s internal parts. What could have lead to wear on the engine internal parts? It is generally caused by an irregular oil change and a low oil level.

As the motor oil flows in the engine, over time, it loses its density, viscosity rating, and lubricating properties. All these lead to engine sludge formation and internal corrosion.

Driving your car with a low oil level will result in low oil pressure and not circulate well where it should. This could result in excessive engine wear and damages. Several other mechanical problems can cause rod knocking. These include;

  • Broken or loose timing chain tensioner
  • Worn out the main bearing
  • Worn water pump bearing
  • Cracked or broken flex-plate or flywheel
  • Worn alternator rotor bearings.

How to diagnose rod knock

Here are practical, proven steps on how to diagnose rod knock.

Check the state of the oil and oil level

  • Locate your engine oil dipstick and pull it out.
  • Clean it with a rag
  • Check the color of the oil. If the color is muddy or dark, you have a dirt engine oil
  • Reinstall the dipstick and pull it out to re-inspect it.
  • Find out the state of your engine oil and level. Dirty engine oil can cause system wear, damages, and engine knocking.

how does rod knock happen

Drain the engine oil and inspect it

Get an oil catch pan close to avoid messing up the entire garage with oil. Before draining it, look at your engine cap to know the oil viscosity your engine uses. This is important, so you don’t replace the old oil with the wrong oil type.

Before draining the old oil, get a transparent container to take one cup of oil so you can take a closer look. After removing the sample for close inspection, drain the rest of the oil.

If you see metal shavings in the engine oil, it is an indication of engine components wear. The metal shavings could come from con rod, crank bearing, or other inner engine components, causing the knocking sound.

If you fail to carry out regularly scheduled oil changes, the oil will get old and start to erode the brass layers on the bearing. This happens mainly on the bearings far from the oil pump because they are getting low oil flow than the bearings closer to the pump.

You should also check the color of the oil. If it is dark brown, the oil is old or dirty and needs to be replaced. And if the oil is too light, consider replacing it. If you want to know how to extend the life of an engine with rod knock – it’s pretty simple. Always change oil at the right interval.

How to fix a rod knock

A rod knock is a sign that a problem lies on the interior components of an engine. Like we explained above, several factors can cause rod knock; some are expensive repairs, while some are not. This doesn’t mean your engine is beyond repair.

However, before consulting your dealership or mechanic, there are few steps you can take to reduce the rod knock and possibly stabilize your engine before carrying out a thorough repair.

Step 1: Carry out Oil Change service

Slide under your vehicle and place a catch pan directly under the draining plug. Get the sizeable socket size and wrench. Locate the draining plug on the crankcase and loosen it to drain the oil.

Drain the oil completely and reinsert the plug (the draining plug is also called a sump bolt)—Torque the sump bolt to the manufacturer’s spec.

Remove the oil filter with an oil filter wrench by gripping the oil filter and turning it clockwise. Fix in a new filter and torque down to recommended specifications. Replace the engine oil with the same oil viscosity rating or recommended oil.

Keep checking the oil as you pour in the new oil if you don’t know how many quarts your engine takes. A four-cylinder engine typically takes around 4-5 quarts.

Step 2: Remove the crankcase and inspect the cod rod bearing

A loosen connecting rod cap will cause knocking noise. Inspect the bolts holding the con rod with the lid and re-torque them. Consider inspecting the cod rod bearing and replace them as needed.

Step 3: Pour fuel-injection cleaner into your gas tank

Grimes and dirt might make their way into your gas tank when you refill your tank at the gas station.  When the fuel pump is transporting gas to the engine, it sends that dirt and grimes along, causing engine knocking.

Cleaning your fuel injection system will clear out those grimes and resolve the rod knock. If you have older vehicles that use carburetors, do not use fuel injection cleaner. Instead, get a carburetor cleaner spray it in the carb.

FAQs:

Q: Can oil change stop engine knocking?

If your oil pressure is low or you have a low oil level, you’ll likely hear a splattering, tickling, or ticking noise from the engine. If this noise is from the valves, or lifters, adding or doing oil change will stop the noise. But unfortunately, if the noise is rod knock, an oil change will not stop it.

Q: Will thicker oil stop rod knock?

As explained earlier, a rod knock is a sound indicating wear and damages to your engine system. So, changing to oil with a higher viscosity rating (heavier or thicker oil) will help eliminate or at least reduce the rod knock. It will potentially prolong your engine life. This doesn’t mean you should not diagnose and fix the cause of the knocking.

Q: How long will an engine last with rod knock?

If you have a rod knock in your vehicle, you might also be asking, ‘how long can you drive with rod knock?’ Regardless of your question, once an engine starts to knock, nothing is too sure to determine how long it will last.

You can have a total breakdown the next time you start your vehicle, or it can keep working for 3-6 months. However, driving with rod knocks for a couple of minutes is not recommended. It can blow up your engine and keep you in the middle of nowhere.

Q: Can you hear rod knock at idle?

Yes, you can hear rod knock upon engine startup, idling, accelerating, and decelerating. The noise will increase as you step on the gas pedal and decrease as you remove your leg. Disregard anyone who says otherwise. Why? Rod knock is a loud banging noise upon engine startup and continues until you turn off the car.

Q: What happens when you hear a rod knocking?

Rod knocking is a problem with the internal engine moving parts. Once it occurs, you’ll hear knocking or banging sounds, have low oil pressure, and check the engine light in your instrument cluster. If you fail to track down the cause and fix it in time, it will result in catastrophic damages to the engine.

Q: Is it worth fixing rod knock?

A rod isn’t a problem that will go out on its own. You should diagnose and fix the problem on time before it escalates. If you notice and fix the rod knock-on time, it won’t dig a hole in your pocket. So, it is worth repairing a rod knock at an earlier stage.

Q: How Much Does It Cause to Fix A Rod Knock?

Several factors influence the cause of fixing a rod knock. These factors include; the actual cause of the rod knock, how severe it is, hours of labor, service fees, the vehicle makes, and models. However, the cause of fixing a rod knock should be around $700-2500.

Final word

Rod knock is one of those complicated engine problems that many folks overestimate, thinking it’s the end of the game with their car’s engine.

If you notice the problem earlier and take immediate action, your dealership or mechanic might resolve the problem without breaking your budget. However, if you notice and ignore the signs highlighted above fixing the issues might cost you a lot. At this point, replacing your engine might be the only option.

Osuagwu Solomon

Osuagwu Solomon is a seasoned automotive technician for the past 9 years, and a technical writer. He loves writing about auto professional repair guides, DIY repair guides, and buyer’s guide. After spending six years in the automotive workshop, he decided to impact his knowledge to people aside his domain, and he has achieved this by centering his Automotive writing skills on REPAIRS.

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