What is Rod Knock?

Our vehicles produce of variety of noises, most of them being completely expected or even worrying when absent. However, some other sounds may be warning you of an issue in your vehicle, potentially even a catastrophic one. Vehicle owners must understand what noises are normal and which you should be keeping an eye out for. 

One of these worrying noises takes the form of a “knocking” sound coming from the engine while running. This is a sign of potential rod knock, which can be one of the most destructive issues in any engine and needs to be dealt with immediately. 

This isn’t to say that any knocking sound from your engine means you have rod knock, as many other issues can lead to a similar sound. However, rod knock is not a problem to let linger, so being able to recognize the potential issue and its effects is important.

What is Rod Knock?

Rod knock refers to the connecting rods knocking against the crank as it makes its rotation. Each connecting rod is connected to the crank with a bearing sitting in between. Between the engine bearings and crank journal sits a tiny gap that allows oil to flow through, creating a thin lubricating film between these components. These gaps, called “tolerance”, are measured in thousands of an inch and are carefully calculated to allow in the perfect amount of oil for the engine. 

Main bearing cap

As this bearing is made of softer metal, it will begin to wear down and increase the size of the gap making it unable to form a proper barrier. As the rod is now looser, it may cause the rod to knock against the crank as the piston changes direction. This is the source of the dreaded “knocking” noise. 

Not only does this issue just cause an annoying noise, but it’s also one of the most potentially destructive conditions for your engine to be in. Rod knock allows oil to leak into the cylinders and lead to it burning off within the cylinder, which will cause issues with the oxygen sensors and emissions systems. 

Furthermore, the rapid consumption of oil may leave your engine starved for oil. Without proper lubrication, the engine will build up an excess of heat and may lead to complete failure.

Symptoms of Rod Knock?

While you can’t diagnose rod knock from symptoms alone in most cases, it’s still important for vehicle owners to recognize the symptoms that may point to it. 

  • Blueish-grey exhaust smoke
  • Rapid oil loss
  • Metal shavings in oil
  • Audible knocking sound

In a vehicle with rod knock, the frequency of this knocking sound will increase and decrease based on the engine’s RPM. If the sound goes away after the motor has warmed up or does not change based on engine speed, you’re most likely looking at something other than rod knock. 

Pistons and connecting rods
160SX, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Can I Drive With Rod Knock?

If you’re experiencing only mild symptoms of rod knock, it may be tempting to continue driving the vehicle until it gets “bad enough” to bring in for repair. 

Unfortunately, driving a vehicle with rod knock is essentially driving a ticking time bomb. While it may not seem urgent at the time, this issue will only progress in severity. It’s impossible to know exactly how bad the issue is without having the engine internally inspected, so even if the symptoms seem to be in their beginning stages your motor may still be on the verge of irreparable damage.

For this reason, you should never drive a vehicle you suspect may have rod knock. Instead, have it towed and inspected at a trusted auto repair facility as soon as possible.

Engine Diagnostics & Repair in Naperville

No matter the issue your engine is facing, the ASE Certified technicians at Becker Service Center in Naperville have the equipment and expertise to take care of your vehicle the right way. We strive to make the auto repair experience as painless as possible, so give us a call or schedule online today to speak with our friendly and knowledgeable service advisors.