HomeAFTERMARKET NEWS9 Common Symptoms Of A Bad Crankshaft Pulley

9 Common Symptoms Of A Bad Crankshaft Pulley

Crankshaft pulleys are not like any other pulleys. They are much more than a simple piece of metal and are much more complex than most people think which can lead to severe consequences when damaged.

What does a crankshaft pulley do?

The crankshaft pulley is mounted on the outermost part of the crankshaft, at the opposite side of the engine’s flywheel. Some engines have an independent harmonic balancer with the crankshaft pulley bolted on to it while other types of engines have a dampener crankshaft pulley that is connected straight to the crankshaft by the timing chain sprocket or the timing belt pulley.

The crankshaft pulley powers the driving belt as it distributes the crankshafts rotational force to the engine accessories (alternator, power steering pump, AC compressor etc…) via the driving belt. Most crankshaft pulleys have a rubber ring between the internal and external parts of the pulley to dampen engine vibrations which come from the crankshaft. This prevents the engine vibrations from transferring to the accessory driving belt.

Most common symptoms of failure

  • Engine Vibration: Crankshaft pulleys that have an integrated harmonic balancer will cause the engine to vibrate if the harmonic balancer or dampening system fails. As the harmonic balancer fails it will stop absorbing the crankshaft’s vibrations that are transmitted to the engine’s accessories. The vibration will get harder as the RPMs get closer to the engine’s resonant frequency. These type of vibrations are harmful to the engine’s accessories, the crankshaft, and other engine internal parts.
  • Rough Idle: The crankshaft pulley is subjected to a high level of stress as the engine is idling. A bad crankshaft pulley can make the engine idle rough. If you notice that the engine is idling unevenly, but you don’t feel any misfires or combustion problems you should probably check the crankshaft pulley.
  • Battery Light On: When the rubber or isolating compound breaks – the crankshaft pulley will catastrophically fail. The inner part will separate from the outer part which is in contact with the drive belt. As the drive belt stops turning, the rest of the accessories powered will stop working. The alternator which is often connected by the drive belt will stop spinning and won’t be able to charge the battery which will cause the battery to light on the instrument cluster.
  • Hard Steering Wheel: Vehicles with hydraulic power steering have a power steering pump that is driven by the drive belt. If the crankshaft pulley breaks apart, the drive belt will stop turning causing the power steering pump to stop working. Without the aid of the power steering pump the vehicle will become hard to turn left and right.
  • AC Compressor Failure: The AC Compressor is also powered by the drive belt which will stop working when the crankshaft pulley brakes.
  • Drive Belt Tensioner Problems: A bad crankshaft pulley dampener will fail to absorb the vibrations properly. This vibration will transfer to the drive belt and the rest of the engine accessories system. The belt tensioner may move excessively trying to keep the belt’s tension constant, but in many cases will fail to do so, which in turn causes the drive belt to “slap” damaging it and ultimately leading to the belt slipping of the pulleys.
  • Transmission or Internal Engine Damage: If the engine has been running with a bad crankshaft pulley for a long time the vibration may damage the transmission, and, in some cases, it can also damage the engine’s internal parts such as the crankshaft bearings. Vibrations may also damage the transmission’s bearings, shaft and gears which often requires the removal of the transmission from the vehicle to be repaired.
  • Drive Belt Edge Damage: A bad crankshaft pulley can lead to the driving belt being misaligned which in turn will be damaging the driving belts edges. This may also cause damage to the idle rollers and non-metallic pulleys.
  • Squealing Noises: In some extreme cases, you may hear squealing, screeching, or whining noises typical of bad drive belts. These noises can also be made by a misaligned and poorly tensioned driving belt. A bad crankshaft pulley may cause the same noises as it can cause the driving belt to be misaligned due to a loss of tension.
A car alternator running hot powered by a serpentine belt.

When should a crankshaft pulley be changed?

A crankshaft pulley is designed to last the lifetime of the engine. However due to wear and tear, high temperatures, exposure to coolant or engine oil (due to leaks), the rubber ring can become damaged. The rubber ring works as a vibration dampener which holds together the internal part to the outer part of the pulley. If you notice that oil or coolant has reached the crankshaft pulley it should be replaced before it fails. If the vehicle starts shaking and you suspect that the crankshaft pulley may be damaged, it would be recommended to take a deeper look at it and replace at the first sign of damage. The consequences of a broken ring can be really serious. It is highly possible that a broken vibration dampener can damage other parts of the engine and even lead to a catastrophic engine failure which is extremely expensive to repair.
The best way to inspect the crankshaft pulley is to remove it. A visual inspection allows checking only on the front side of the pulley, leaving the backside of the pulley unchecked which may lead to a wrong diagnosis. If the pulley is already out from the engine it is cheaper in the long run to replace it in case there might be something wrong with it.

About BGA (BG Automotive):

BGA is an Automotive Aftermarket parts supplier, celebrating over 90 years of OE manufacturing heritage as the aftermarket division of the largest privately owned OE supplier, 4BG Group, established in 1929.

BGA focuses on providing one of the largest ranges of high quality, competitively priced parts in the aftermarket containing Auxiliary Drive, Camtrain, Cooling, Gaskets, Lubrication, Power Steering, Steering & Suspension, Timing Belt Kits, Timing Chain Kits and Transmission.


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