Symptoms and causes of connecting rod knock
Unusual engine noises can be a cause for concern, but not all of them indicate a serious defect. If you experience this type of noise, or “connecting rod knock”, you should take immediate action. This loud metal-on-metal knocking sound indicates serious internal damage and can put your engine at risk of complete failure if you continue to operate it.
In this guide, we’ll take a closer look at what causes connecting rod knock, its symptoms, and how much it costs to repair (hint: it’s expensive). We’ll also explain some less serious problems that are often misdiagnosed as connecting rod knock, so you don’t waste your money.
What is connecting rod knock?
Connecting rod knock is a noise that occurs inside an engine crankcase when there is excessive play between one or more of the engine’s connecting rods and their corresponding journals. This is the result of end-stage bearing wear, which results in the connecting rod rattling against the crankshaft itself.
As the engine’s crankshaft rotates, the connecting rod in question moves back and forth on its journals to compensate for the existing play. This happens very violently, creating an audible noise. This noise can often be heard from far away.
Connecting rod knock can affect vehicles of any manufacturer, including popular brands such as Toyota, Subaru, Chevrolet, Dodge, and Ford, but unfortunately, once the condition appears, it can worsen over time. In severe cases, connecting rod knock can even cause pistons and connecting rods to pop out if left untreated.
What does connecting rod knock sound like? Connecting rod knock sounds like a loud metallic knock or banging noise that increases in speed with engine RPM. Additionally, this knocking often causes actual engine vibrations that can be felt by hand. Unlike other internal engine noises, connecting rod knocking does not subside after warming up.
Symptoms of Connecting Rod Knock There are several symptoms associated with connecting rod knock. Recognizing these symptoms can help you properly diagnose the current condition and get your vehicle back to the shop sooner. Below are some of the most common symptoms associated with connecting rod knock.
1) You hear a “knocking” sound
The most obvious symptom of connecting rod knock is the knocking noise for which the condition is named. The connecting rod knock is very loud and sounds like a deep metal banging sound. This noise usually increases in tandem with engine speed and gets louder as the condition progresses.
2) Noticeable vibration
In severe cases, you can often feel or hear the connecting rod knocking. This occurs when the affected connecting rod strikes its corresponding journal back and forth with considerable force. Once this type of vibration occurs, it can worsen over time and distance.
3) Oil Pressure Abnormalities
In some cases, noticeable oil pressure abnormalities can also be caused by the presence of worn bearings, such as the bearing that causes the connecting rod knock. This occurs when oil flows too freely through loose or worn bearings, resulting in it not gaining enough pressure to flow through.
What causes connecting rod knock? The most common cause of connecting rod knock is, without exception, a severely worn connecting rod bearing. However, this condition itself can lead to many underlying problems.
The most common cause of connecting rod bearing wear is oil-related problems, which ultimately affect the lubrication of the bearing. Below are some of these most common problems:
– Incorrect oil viscosity
– Clogged oil channels
– Low oil pressure
– Engine oil that is too hot
In addition, extreme engine driving can also lead to premature wear of connecting rod bearings. This includes over-revving the engine or operating it continuously at high speeds. Such engine operation causes excess heat to build up in the engine bearings, accelerating wear and ultimately causing failure.
Can I drive with connecting rod knock? In any case, you should never drive your vehicle if you hear or suspect a connecting rod knock. Continuing to drive your vehicle in this condition can cause the damage associated with such an issue to progress rapidly. If the connecting rod comes loose from the engine crankshaft and jumps out of the block, it will prevent an engine overhaul.
What can be confused with connecting rod knock?
When you hear strange noises coming from under the hood of your car, it’s natural for your mind to wander and focus on worst-case scenarios. For this reason, many abnormal engine noises are often confused with connecting rod knock, causing a lot of unnecessary panic.
It’s important to distinguish between different engine sounds to avoid misdiagnosing the problem at hand. Given the severity of repairing this type of fault, misdiagnosis at this point can be very costly. The most common sounds confused with a connecting rod knock are:
– Plunger “clicking”
– Pre-ignition noise
– Valve rattle (valves not adjusted correctly)
– Piston rattle
