Rebuilt MG521 Transmissions Available for Immediate Purchase

The Twin Disc MG521 rebuilt marine transmission represents the perfect balance of power, precision, and durability for a wide range of demanding marine applications. With a power handling capacity of 427 to 990 horsepower (318 to 738 kW), this transmission is designed to keep your vessels operating smoothly and reliably in commercial fishing, offshore support, workboats, and patrol applications.

Now available for immediate sale, each rebuilt unit is restored to OEM specifications, rigorously tested, and supported by Diesel Pro Power’s commitment to quality and performance.

Twin Disc MG521 Ratios for Sale

Our rebuilt Twin Disc MG521 units are offered in the following gear ratios, each one meticulously rebuilt and tested to ensure optimal performance and durability. These units are available for immediate sale, minimizing vessel downtime and ensuring your operations remain efficient and reliable.

• Twin Disc MG521 marine transmission ratio 2.00:1 – rebuilt
  This ratio is ideal for vessels that prioritize a balance between speed and torque, such as pilot boats, high-speed workboats, and fast patrol craft. It provides a strong mix of responsiveness and pulling capacity, making it a versatile option for operators who require a quick response in varying conditions.

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• Twin Disc MG521 marine transmission ratio 3.00:1 – rebuilt
  Perfect for fishing trawlers, mid-sized commercial vessels, and service boats, this ratio offers enhanced torque for pulling power without sacrificing too much speed. It strikes an excellent balance, ensuring reliable performance in vessels that encounter variable load conditions and require steady propulsion.

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• Twin Disc MG521 marine transmission ratio 3.50:1 – rebuilt
  Designed for more heavy-duty applications, including large trawlers, utility boats, and offshore support vessels, this ratio delivers higher torque at lower input speeds. It is particularly well-suited for vessels that operate with heavy payloads or under constant load, ensuring consistent power and efficiency.

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• Twin Disc MG521 marine transmission ratio 4.00:1 – rebuilt
  The highest torque ratio available in our MG521 offerings, this configuration is ideal for vessels with extreme load requirements, such as heavy-duty tugs, large fishing vessels, and certain offshore applications. It ensures maximum pulling power and durability, especially in challenging marine environments.

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Each of these rebuilt transmissions is in stock, fully refurbished to OEM specifications, and backed by a refundable core deposit. Our commitment to quality means you can install your MG521 with confidence, knowing it has been rigorously tested and is ready to handle the demands of your specific vessel type.

By offering this comprehensive range of gear ratios, we ensure that marine operators can select the precise configuration that best suits their vessel’s engine specifications, operational profile, and performance requirements. Whether you need high speed, balanced torque and speed, or maximum pulling power, the Twin Disc MG521 has a ratio designed to meet your exact needs.

Key Features and Benefits

• Oil-Controlled Clutch Engagement: For smooth gear changes under load.
• Carburized, Hardened, and Ground Gears: Ensures longevity and low maintenance.
• Emergency Come-Home Capability: Enables limited propulsion in clutch failure scenarios.
• Rubber Block Drive: Reduces vibrations and mitigates misalignment stress.
• Dry Flywheel Housing: Simplifies maintenance and access.
• Clutches Removable with Transmission Installed: Eases servicing and reduces downtime.
• Identical Ratios Forward and Reverse: Consistent performance in both directions.
  

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Engine Compatibility for the Twin Disc MG521

The Twin Disc MG521 rebuilt marine transmission is engineered to integrate seamlessly with high-output diesel engines delivering between 427 and 990 horsepower, making it a robust and versatile choice for vessels requiring continuous, reliable performance. Careful selection of the engine-transmission pairing ensures optimal power transfer, fuel efficiency, and operational longevity. Below are detailed, compatible engine models from leading manufacturers:

Caterpillar Engines

• C12: Producing between 345 and 715 hp, the C12 is a proven workhorse in marine applications. It offers excellent fuel efficiency and compact design, making it ideal for fishing vessels, patrol boats, and light-duty workboatswhere reliable power and maneuverability are essential.
  

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• C13: Delivering 385 to 750 hp, the C13 provides a balance of high power and efficiency. It’s widely used in high-speed ferries, pilot vessels, and offshore support boats, offering a durable, high-torque solution for demanding marine environments.
  

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• C15: Ranging from 435 to 850 hp, the C15 is a favorite for trawlers, large workboats, and utility vessels where sustained performance under load is crucial. Its robust design handles extended operational hours and varying load conditions with ease.
  

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• C18: Offering up to 1000 hp, the C18 is at the top end of the MG521’s compatibility, suitable for offshore support vessels, tugs, and large fishing boats. It delivers exceptional torque, particularly in heavy-duty and continuous-duty applications.

Cummins Engines

• QSM11: With a range of 300 to 715 hp, the QSM11 offers flexibility for mid-duty commercial vessels such as pilot craft, workboats, and fast ferries. Its reliable performance and fuel efficiency make it a solid match for MG521 in diverse applications.
  

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• QSK19: Delivering 500 to 800 hp, this engine provides consistent, high-output performance, making it ideal for heavy-duty vessels, including supply boats and trawlers that require dependable power for long-range operations.
  

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• KTA19: Generating 450 to 700 hp, the KTA19 is a tried-and-true choice for workboats, patrol boats, and mid-sized commercial vessels. Its durable design is well-suited for operations where long engine hours and constant load are common.
  

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• KTA38: Producing between 750 and 1000 hp, the KTA38 sits at the upper range of the MG521’s capacity. It is a strong match for large commercial vessels, including dredgers, tugs, and offshore supply vessels, where high torque and durability are required.
  

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Detroit Diesel Engines

• 8V92TA: Providing 350 to 550 hp, this turbocharged V8 engine offers a balance of power and compact design, commonly used in medium-duty commercial vessels, such as pilot boats and small ferries.
  

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• 12V92TA: Delivering 525 to 750 hp, the 12V92TA is ideal for larger fishing vessels, supply boats, and workboats requiring high power and reliability. Its proven track record in marine environments makes it a solid match for the MG521.
  

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• 16V92TA: With outputs up to 850 hp, the 16V92TA is designed for heavy-duty marine applications, including large trawlers, offshore support vessels, and commercial tugs. It provides excellent power density and resilience under load.
  

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• Series 60 (12.7L): Offering 350 to 600 hp, the Series 60 is a popular choice for a wide range of mid-sized marine vessels, known for its fuel efficiency and adaptability. It’s a reliable option for vessels needing a balance of power and economy.

SAE Housing Details

• Housing: SAE 0 standard, ensuring compatibility with a broad range of engine configurations. An adapter is available for SAE 00, enabling integration with larger engine models that demand additional mounting strength and stability.
  

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• Certified Installation Print: Drawing X9664-G provides detailed installation specifications, ensuring correct alignment and secure mounting for the MG521.
  

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• Approximate Dry Weight: 998 kg (2,200 lbs), which highlights the need for proper lifting equipment and vessel structural support during installation.
  

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• Mounting Dimensions: Length: 850.9 mm (33.50 in); Height: 528.6 mm (20.81 in); Width: 228.6 mm (9.0 in), ensuring a compact yet robust design that fits a variety of marine engine rooms.

Duty Classification Performance Information

Continuous Duty (Workboat Applications)

Intermediate Duty (and Pleasure Craft Service)

Pleasure Craft (Planing Hull)

Heat Exchanger Kits

• Fresh Water: Kit K-98
• Raw Water: Kit K-99

Installation and Maintenance

Proper installation and maintenance of the Twin Disc MG521 are essential to ensure optimal performance, safety, and longevity. Below is a comprehensive guide highlighting key procedures and best practices:

• Use Certified Installation Print X9664-G: This print provides precise specifications for aligning the transmission with the engine flywheel housing, ensuring correct torque application and secure mounting. Incorrect alignment can cause premature wear, excessive vibration, and operational inefficiencies. It is recommended that installation is performed by certified marine mechanics familiar with the specifications.
  

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• Cooling Systems: To maintain optimal operating temperatures, always install the appropriate heat exchanger kit. Use Kit K-98 for fresh water cooling and Kit K-99 for raw water cooling. Maintaining proper cooling prevents overheating, which can degrade clutch performance, damage seals, and shorten the lifespan of the transmission. Routine checks of the cooling system’s integrity and coolant levels are vital.
  

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• Routine Maintenance: Scheduled maintenance is crucial for preventing unexpected failures. Replace transmission oil and filters at intervals specified by Twin Disc to keep the lubrication system clean and efficient. Regularly inspect and replace clutch plates and seals to ensure consistent engagement and prevent leaks. Check alignment between the engine and transmission frequently, especially after extended operation or maintenance, to prevent stress on the drivetrain.
  

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• Lifting and Handling: The MG521 weighs approximately 998 kg (2,200 lbs), necessitating the use of certified lifting equipment during installation or removal. Ensure the vessel’s structural integrity can support the transmission’s weight. Use slings, spreader bars, or lifting eyes per manufacturer recommendations to avoid damaging the transmission housing or components.
  

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• Environmental Considerations: When operating in harsh environments such as offshore or heavy commercial applications, consider more frequent inspections and oil changes due to increased exposure to contaminants and high load conditions. Use only approved lubricants and OEM-specified parts to ensure compatibility and performance.
  

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• Operator Training: Ensure that vessel operators are trained on proper shifting procedures and are familiar with the transmission’s operating parameters. Avoid aggressive shifting or prolonged operation outside recommended RPM ranges, which can increase wear and reduce service life.

Service Classifications

Understanding the correct service classification for your vessel helps determine maintenance schedules and load expectations:

• Continuous Duty: This classification applies to vessels that operate at full rated power for extended periods, such as tugs, ferries, and offshore supply vessels. In this mode, the transmission operates under constant load, requiring rigorous maintenance and high-quality lubricants to prevent heat buildup and wear.
  

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• Intermediate Duty: Vessels in this class, including fishing boats, pilot craft, and patrol vessels, experience a combination of high-power operation and reduced load intervals. Maintenance intervals may be slightly extended compared to continuous duty, but operators should remain vigilant about monitoring performance indicators and addressing early signs of wear.
  

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• Pleasure Craft: Designed for vessels such as planing hulls and recreational boats that operate at high power in short bursts. While these vessels may not experience constant load, sudden power demands can cause stress on the transmission. Regular maintenance is still critical to ensure reliability, especially before long trips or extended periods of use.

Important Notice

The performance data and product information provided herein are intended solely as general guidelines. Diesel Pro Power assumes no responsibility for system-related issues or failures resulting from improper selection, installation, or maintenance of rebuilt transmissions. It is the responsibility of the purchaser and installer to ensure compliance with all safety standards, to use proper engineering judgment, and to consult with qualified marine engineers to ensure that the transmission is compatible with the specific vessel configuration and operating conditions.

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