Repair of Intermediate Shaft

Intermediate Shaft Damage in Marine Propulsion Systems

The intermediate shaft is a critical component of the vessel's propulsion system, transmitting power from the main engine to the propeller shaft. During service, we regularly encounter intermediate shafts with damaged bearing seating areas caused by bearing failure, inadequate lubrication, prolonged operation, or misalignment.

If these conditions are not addressed promptly, the shaft journal develops scoring, taper, ovality, and localised wear. Continued operation can increase vibration, affect shaft alignment, and lead to further damage to the propulsion shafting system. Often, the shaft can be repaired without replacement, provided the damage remains within OEM regrind limits.

Intermediate shaft repair

Common Causes of Intermediate Shaft Damage

Insufficient Lubrication

One of the most common failures we investigate is inadequate lubrication between the white metal bearing and the intermediate shaft. Once the lubricating oil film breaks down, metal-to-metal contact occurs, resulting in scoring, wear marks, and damage to the bearing seating area. If the vessel continues operating under these conditions, the journal dimensions may exceed the manufacturer's permissible limits.

White Metal Bearing Failure

White metal (Babbitt) bearings have a defined service life. Bearings that continue operating after significant wear or deterioration frequently damage the intermediate shaft journal. We often find wiping of the bearing surface, localized overheating, and wear on the shaft seating area, requiring precision machining before the shaft can be returned to service.

Inspection Before Repair of Intermediate Shaft

Every repair begins with a detailed inspection to determine the condition of the shaft and whether in situ machining of intermediate shaft is feasible.

Our inspection includes:

Dimensional inspection of the intermediate shaft, propeller shaft, and tail shaft to measure taper and ovality.
Magnetic Particle Inspection (MPI) of the bearing seating area for crack detection.
Hardness testing to identify any variation in hardness caused by bearing failure.
Measurement of the journal dimensions and surface finish before machining.

The inspection results determine the machining allowance and confirm whether the shaft remains within OEM repair limits.

In Situ Repair of Intermediate Shaft

Where operating conditions permit, we carry out in situ crankshaft Grinding onboard the vessel using portable machining equipment. This avoids unnecessary dismantling of the propulsion shafting and significantly reduces vessel downtime.

During machining, we continuously monitor journal dimensions to ensure the repaired shaft remains within specified tolerances. We pay particular attention to taper, ovality, bearing seating geometry, and the final surface finish required for reliable bearing operation.

Grinding and Polishing of the Bearing Seating Area

The damaged bearing seating area is restored through controlled grinding followed by precision polishing.

During this process, we ensure:

The final surface finish after grinding and polishing is maintained at less than 30 Ra value.

Taper, ovality, and journal dimensions are verified throughout

The machining process maintains proper bearing contact and hydrodynamic lubrication.

White Metal Bearing Rebabbitting

Where inspection confirms that the white metal babbitt bearing cannot be reused, we carry out rebabbitting in our workshop using the centrifugal casting system in accordance with international standards.

After rebabbitting, the bearing is machined, inspected, and prepared for installation. Where required, we also undertake bearing fitment to ensure correct clearance and alignment with the repaired shaft journal.

Final Inspection

Before the shaft is returned to service, all critical dimensions are verified. Journal size, taper, ovality, hardness, surface finish, and bearing fitment are inspected to confirm compliance with OEM tolerances and the applicable Classification Society requirements.

All repairs are executed with guarantee.