From Two Damaged Gearboxes to One Working Spare: A Lifecycle Solution

Overview

Two Twin Disc MGX-5114SC gearboxes were received at MIT‘s Hensall workshop from a vessel operated by a Scottish salmon fishery after developing faults in service. Both units had sustained significant structural damage from rope-pull loading during aquaculture operations, leaving the gearboxes non-functional upon arrival.

Following a full strip-down and inspection of both damaged units, MIT used approved serviceable components from each gearbox to rebuild a single reconditioned MGX-5114SC gearbox. Any remaining serviceable components were returned to the Scottish salmon fishery to support its spare parts inventory.

Project Specifications

Type of Project: Marine Gearbox Rebuild / Marine Gearbox Overhaul

Location: MIT Hensall Workshop

Industry: Aquaculture

Gearboxes: Twin Disc MGX-5114SC

Initial Inspection & Findings

Both gearboxes arrived in a non functioning condition and were stripped for detailed inspection. During disassembly, MIT engineers carried out crack testing, runout measurements, and component condition assessments throughout both transmissions.

The most significant finding was extensive cracking around both gearbox housings. The damage was severe enough that neither housing could be returned to service, meaning a new housing would be required for the rebuild.

Further inspection identified:

• Cracked manifold and damaged manifold sleeves
• Chipped output gear teeth
• Worn clutch plates
• Worn input flange splines
• Bearing wear, along with deteriorated seals and O-rings

Despite the extent of the damage, inspection and crack testing confirmed that several major internal components, including pinion gears and clutch assemblies from one gearbox, remained serviceable and suitable for reuse.

Engineering Assessment

Detailed inspection, crack testing, and dimensional measurements of both MGX-5114SC gearboxes confirmed extensive cracking in both housings, rendering them unsuitable for further service. However, several major internal components remained within specification and suitable for reuse.

This component-level assessment gave MIT a clear, technically sound rebuild strategy. Damaged and worn parts were removed from service, while approved serviceable components from both transmissions were retained to rebuild a single reconditioned MGX-5114SC gearbox.

Marine Gearbox Rebuild & Reconditioning

Following approval, MIT rebuilt one MGX-5114-SC gearbox in accordance with manufacturer specifications and guidelines. The rebuild included replacement of:

• Main housing
• Bearings
• Seals
• Clutch plates
• Manifold sleeves
• Filter element

Damage to the input and output seal tracks was also repaired during assembly. Bearing preload, clutch clearances, and shaft runout measurements were checked against specification throughout the rebuild process.

Furthermore, serviceable components recovered during the strip-down were incorporated where appropriate during the rebuild. Any additional serviceable components were boxed and returned to the customer to support its own spare parts inventory.

Testing & Results

After assembly, the reconditioned gearbox underwent workshop testing to verify performance and engagement characteristics. Clutch engagement pressures, timing, shaft clearances and bearing preload values were recorded and confirmed within specification.
The gearbox successfully completed workshop testing, completing the rebuild of a reconditioned gearboxes for use as a working spare.

Detailed Outcome

• Two non-functioning MGX-5114SC gearboxes fully stripped and inspected
• Structural housing damage, manifold defects, gear tooth damage, and drivetrain wear identified
• Serviceable components recovered and reused where appropriate
• One reconditioned gearbox rebuilt to manufacturer specification for use as a working spare
• Additional serviceable components returned to Scottish Sea Farms for future spares stock
• Unnecessary material replacement reduced through component recovery and reuse
• Reconditioned gearbox successfully completed workshop testing

Key Takeaway

Through detailed inspection, crack testing and component-level assessment, MIT developed a rebuild strategy that enabled the creation of a reconditioned MGX-5114SC gearbox for use as a working spare.

By combining approved serviceable components with new replacement parts where required, the project strengthened operational resilience, maximised the value of existing assets and reduced unnecessary material replacement through responsible component reuse.

Planning a Marine Gearbox Overhaul or Working-Spare Strategy?

MIT delivers expert inspection, repair, marine gearbox overhaul, and reconditioning services for marine transmissions across the commercial marine and aquaculture sectors.

From detailed condition assessment to complete rebuilds, our OEM-trained engineers help operators maximise equipment reliability, plan for future maintenance requirements and minimise downtime.

Speak to our team today to discuss your gearbox overhaul, working-spare or maintenance requirements.