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Loose Shaft Nut Turbo Failure

About a Loose Nut Shaft

During the assembly of a turbocharger, a shaft nut holds the compressor wheel and other rotor group parts onto the shaft. The shaft nut is a machined part, which must be tightened to a specific torque. A shaft nut is normally left-hand thread, unless the rotor parts are reverse rotation. A shaft nut can also be referred to as a "locknut" or an "impeller locknut."

Turbochargers are a precision engineered object and are designed to operate at speeds of up to 360,000 rpm while also reaching temperatures of up to 850 C in diesel applications and up to 1050 C in petrol applications. Operating under such extreme conditions, it is easy to see how failures can occur and how it is easy to misdiagnose a loose nut shaft.

If there is any kind of resistance or locking up within the rotor, then the centrifugal force/inertia continues and the shaft nut will eventually come loose. When the nut shaft comes loose, it can result in catastrophic damage to the compressor wheel within seconds of the turbocharger starting up.

Signs of Loose Shaft Nuts

Here are the most common signs of loose shaft nuts.

  • Loss of performance for the vehicle.
  • Chipping to the compressor blades.
  • Noise from the turbo during use.
  • Burst wheel.
  • Pitting around the compressor inlet.
  • Pitting on the compressor blades.

Causes of Loose Shaft Nuts

Here are some of the common causes that can lead to loose shaft nuts and subsequently turbo failure.

  • Speeding can cause excessive radial expansion of the compressor wheel, but shortens its length. What this does is relax the tension on the shaft and the shaft nut begins to loosen.
  • Scoring to bearings, potentially caused by oil contamination or another failure mode, will allow for the compressor wheel to rub and stall against the housing. This will eventually loosen the shaft nut.
  • Foreign object damage to the compressor and/or turbine wheel puts the turbo out of balance, which allows it to rub against the housing and will ultimately loosen the shaft nut.
  • Any blockage in the oil feed pipe can cause the bearing system to grab onto the shaft, which prevents it from rotating, which in turn causes the shaft nut to loosen.
  • Accidental contamination of new oil while in service.
  • In the vast majority of turbochargers, the shaft nut thread direction is opposite to the direction of rotation on the shaft. If the compressor wheel rotates clockwise, then the shaft nut threads should be left-handed. If that is not the case, then the nut has the potential to become loose during its use.

Prevention of Loose Shaft Nuts & Turbo Failure

Here are some simple measures you can take in order to prevent turbo failure that is caused by loose shaft nuts.

Always change the oil and filter when fitting a turbocharger. Make sure to use the correct grade that is specified by the vehicle manufacturer.

Using the correct torque settings on the shaft nut.

Preventing failure from a loose shaft nut is not straightforward. Keeping the engine in good, working condition and correctly installing the turbocharger is the only way to fully prevent any issues, which is what you'll get when you turn to Long Island Turbo. Professional turbo installation. Any time. With no need to worry about poor operation.

How are the Shaft Nuts Secured?

There are strict guidelines and procedures for the shaft nut tightening operation, where each model has its own specified torque setting and instructions to be carried out by the assembly team. Here are the three steps for securing shaft nuts.

  1. Apply required torque setting.
  2. Loosen the shaft nut.
  3. Tighten up the specified torque, which can be a final torque or a pre-torque with an added angle in order to create the correct amount of tension between the shaft nut and the shaft itself.

With this tightening procedure in place and extensive operator training, manufacturing of turbos has never been safer and more secure. These manufacturers have made a loose shaft nut a highly unlikely cause of turbo failure.

Need Turbo Repair?

If you do happen to have turbocharger engine failure, do not hesitate to reach out to LI Turbo. Request a quote today for the parts and service you need.

Request a Quote

When you reach out, we can provide you with a fair and accurate quote for the repair work.

More Information About Turbo Failure

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