Locomotive Napier SA085 Turbocharger Overhaul

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Background

The locomotive operator asked us to overhaul their Napier SA085 turbocharger, which includes full dismantle, inspection, clean, rebuild and testing.

Solution

Upon arrival, the turbocharger was initially inspected to determine if there were any signs of major damage. The item was found to be in poor condition due to heavy carbon deposits and rust damage. The casting was etched with a unique serial number for identification purposes during the rebuild.

Initial Inspection

The turbocharger was fully dismantled and the internal components were visually inspected. The following faults were found during this process:

1. Extensive carbon deposits were found on the inside of the nozzle ring assembly

Excessive carbon on nozzle ring

2. There is fretting on the compressor wheel adjusting shim

Fretting on compressor adjusting shim

3. All internal gaskets on the turbine side are broken. Exhaust gas has also been escaping into the bearing housing bolt holes

Broken gasket on turbine side

4. The inside of the turbine outlet casing was wet, with a small amount of oil found in the base of the casting hollow

The exhaust inlet housing, nozzle ring assembly and various other internal components were chemically cleaned order to remove any carbon deposits and rust damage that had been found.

The housings were also bead blasted in the area of the internal webs after the nozzle rings were removed.

Once the initial cleaning process had been completed, the rotor assembly was also bead blasted for further inspection.

It was found that there were abrasions to various blades and damage to the tip of one of the blades.

It was also found that the damper wire is broken and snapped and there is slight pitting damage to all of the blades. The journal had also sustained scoring damage

After this process had been completed, the inlet housing was shot blasted and crack detected. It was found that the internal webs running down the fillets were cracked.

Crack found on an internal web

Outcome

Due to the fretting that had been found on the compressor wheel adjusting shim, the item was stoned flat before the shaft assemblies were balanced.

All of the threads that were found to be below the manufacturer’s specification were re-tapped or replaced as per the standard overhaul procedure. All internal special gaskets were replaced as they were not reusable.

The turbine blades were all removed in order to rectify the pitting damage found on inspection.

The blades were also removed so that the damper wire could be renewed. The blades were all redressed and the scored journals were polished.

In order to rectify the cracks that were identified in the housing, the unit was welded prior to refitting.

All internal parts subject to corrosion were painted using red oxide.

Napier SA085 Turbocharger Rebuild process, painted red oxide

The turbocharger was then reassembled using all new replacement parts. The unit was then painted and placed in despatch in preparation for packing and sending to the client, after which the unit was externally finish painted and move to despatch.

Quality Assurance

Once the rotor assembly had been repaired and the turbine blades were refitted, this was then checked for free rotation and balanced. No issues were recorded during this process.

During the rebuild process, the turbocharger casing was then pressure tested at 50 PSI for 30 minutes

Items Repaired/Replaced

1. Bearings – Replaced
2. Joints & Seals – Replaced
3. Bearing Turbine End – Replaced
4. Tab washers – Replaced
5. Nuts – Replaced
6. Shroud Washer – Replaced
7. Rotor Assembly – Repaired
8. O ring – Replaced
9. Exhaust Inlet Housing – Repaired
10. Nozzle Ring Assembly – Repaired

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