How to know when a rod or main bearing is bad

Written by sarah davis
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How to know when a rod or main bearing is bad
Engine bearing problems can be diagnosed by listening. (Jupiterimages/Comstock/Getty Images)

The rod and the main bearings are located in an automobile engine. These bearing are used to protect the crankshaft, or connecting rod. The bearings help the shaft to spin freely inside the engine. When these bearing go bad, glaring signs will let you know they are bad or heading in that direction. One glaring sign is a noise that sounds like knocking. Faulty engine bearings need to be replaced as soon as they go bad.

Skill level:
Moderately Easy


  1. 1

    Insert the vehicle's key into the ignition and start the car.

  2. 2

    Roll down the window to give you a better chance at hearing any noises. Some newer cars have almost no engine noise inside the passenger area, and it may be difficult to hear any engine noises without the window down.

  3. 3

    Listen for any kind of knocking noise coming from the front end of the vehicle. If there are sounds, and they continue once the engine is running, it may be a faulty main bearing. A low oil pressure warning light may accompany a faulty main bearing.

  4. 4

    Listen for a knocking noise that sounds more like striking tin or aluminium and increases as the vehicle accelerates. It is probably a faulty rod bearing.

Tips and warnings

  • If your car is experiencing any of these symptoms, take it to a qualified professional immediately.
  • Faulty rod bearings may result in the engine needing to be rebuilt as well as the bearings.
  • Faulty main bearings will require replacing the crankshaft and all the bearings.

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