Twin Disc MG 521 Marine Transmission Parts

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Twin Disc MG521 Marine Transmission Reb uilt Transmissions & Parts Catalog

Introduction: Premium-Quality Parts for Smooth, Reliable Marine Performance

The Twin Disc MG521 marine transmission is renowned for its robust construction, smooth power transfer, and long-lasting reliability. It’s designed to meet the demands of a wide range of marine applications, including fishing boats, tugboats, workboats, and offshore supply vessels.

At Diesel Pro Power, we provide a comprehensive selection of MG521 parts, including rebuilt transmissions, overhaul plate kits, gasket sets, plate kits, rubber blocks, and oil pump and filter assemblies. Our commitment to exceptional quality, fast shipping, and expert support ensures your MG521 transmission remains operational with minimal downtime.

Rebuilt Twin Disc MG521 Marine Transmissions for Sale

Our rebuilt Twin Disc MG521 marine transmissions are meticulously reconditioned to meet and exceed OEM specifications, ensuring smooth, reliable operation and long-lasting durability. Each rebuilt unit undergoes complete disassembly, thorough inspection, precision reassembly using high-quality components, and rigorous testing to ensure optimal performance under real-world conditions.

Every rebuilt MG521 transmission comes equipped with essential components, including:

Mechanical selector valve assembly (control valve) – For precise, responsive gear shifting and reliable power transfer.
Pilot housing flange – Ensures secure, stable mounting between the transmission and engine.
Oil pump – Maintains continuous oil flow, providing critical lubrication to reduce friction and extend component life.
Oil level gauge – Facilitates easy monitoring of fluid levels, promoting regular maintenance.
Output flange – Provides a secure connection to the propeller shaft, ensuring efficient and reliable power transfer.

Note: Drive ring is sold separately. All rebuilt MG521 transmissions are sold with a refundable core deposit. See details for more information.

Twin Disc MG521 Marine Transmission 2.0:1 for Sale

The 2.0:1 ratio strikes an excellent balance between speed and torque, making it a versatile choice for commercial fishing boats, mid-sized workboats, and recreational vessels. It offers efficient cruising performance while maintaining adequate thrust for typical operational conditions. Vessels that require smooth maneuverability combined with fuel efficiency benefit greatly from this ratio. It’s ideal for operations where moderate load and quick responsiveness are essential.

Twin Disc MG521 Marine Transmission 3.0:1 for Sale

The 3.0:1 ratio provides enhanced pulling power, delivering superior torque for vessels that handle heavier loads, such as utility vessels, offshore supply boats, and larger fishing vessels. This ratio is ideal for applications where strong propulsion is needed for towing, hauling, or operating in challenging conditions with variable loads. The 3.0:1 ratio ensures a balance between dependable thrust and manageable speed for operators needing both power and versatility.

Twin Disc MG521 Marine Transmission 3.5:1 for Sale

The 3.5:1 ratio offers even greater torque, making it suitable for larger workboats, trawlers, and vessels engaged in demanding operational conditions. This ratio excels in scenarios where enhanced control and strong power delivery are essential, such as rough seas, heavy payloads, or continuous operations. Vessels equipped with the 3.5:1 ratio benefit from improved handling and stability while maintaining reliable fuel economy and power output.

Twin Disc MG521 Marine Transmission 4.0:1 for Sale

The 4.0:1 ratio delivers maximum torque and exceptional control, making it the go-to choice for tugboats, large cargo vessels, offshore support craft, and other heavy-duty marine operations. This ratio excels in situations where powerful, steady propulsion is required for maneuvering in ports, towing large loads, or maintaining position in strong currents. Its high torque output ensures smooth and confident operation under even the most demanding marine conditions, providing peace of mind and superior performance for vessel operators.

Our Selection of Twin Disc MG521 Parts

Overhaul Plate Kit – For Twin Disc MG521 Transmission

Our overhaul plate kit includes all the brass friction plates and steel plates needed for a complete clutch rebuild, restoring smooth engagement and consistent transmission performance. Designed to withstand high loads and continuous use, this kit ensures long-term operational efficiency.

Gasket Set – For Twin Disc MG521 Transmission

A complete gasket set featuring main housing gaskets, O-rings, seal rings, and auxiliary gaskets. These components ensure a leak-free seal, maintaining system pressure and integrity during maintenance or overhaul. Manufactured from premium materials for durability in harsh marine environments.

Plate Kit – For Twin Disc MG521 Transmission

A selection of individual brass and steel plates for targeted clutch repairs. Ideal for addressing specific wear or damage, this kit offers a cost-effective solution for maintaining smooth clutch performance.

Rubber Blocks (Couplings) – For Twin Disc MG521 Transmission

The rubber block, also known as a torsional isolator, connects the transmission output flange to the propeller shaft. It effectively absorbs vibrations, reduces stress on drivetrain components, and compensates for misalignments caused by hull flex or engine movement. Made from durable, marine-grade materials for long-lasting performance.

Oil Pump and Filter – For Twin Disc MG521 Transmission

The oil pump and filter assembly ensures consistent lubrication and filtration of transmission fluid, reducing wear on internal components and extending transmission life. The oil pump maintains continuous oil flow under demanding conditions, while the filter removes contaminants for optimal system performance.

Why Choose Diesel Pro Power for MG521 Parts?

24-Hour Worldwide Shipping: Orders are processed and shipped quickly to minimize vessel downtime.
Extensive Inventory: We carry a comprehensive selection of MG521 parts in stock and ready to ship.
Expert Customer Support: Our team provides guidance on product selection, installation, and maintenance.
Over 15,000 Satisfied Customers: Trusted by marine operators and mechanics worldwide for quality parts and reliable service.
Easy Online Shopping: Our user-friendly website makes it simple to browse, select, and order parts from the comfort of your home or office.

Frequently Asked Questions (FAQs) about the Twin Disc MG521

1. What types of vessels use the MG521 transmission?

The MG521 is used in a variety of vessels, including fishing boats, tugboats, offshore supply vessels, workboats, and recreational vessels.

2. What essential parts should I have on hand for MG521 maintenance?

Essential parts include the rebuilt gear, overhaul plate kit, gasket set, plate kit, rubber blocks, and oil pump and filter.

3. What’s included in the overhaul plate kit?

A complete set of brass friction plates and steel plates, designed to restore smooth clutch engagement and reliable performance.

4. How fast can I get MG521 parts from Diesel Pro Power?

We offer 24-hour worldwide shipping, ensuring fast delivery to your location.

5. Are Diesel Pro Power’s aftermarket parts reliable?

Yes! Our parts are engineered to meet or exceed OEM standards, providing dependable performance and longevity.

6. How do I know which parts I need for my MG521?

Our website makes it easy to find parts specific to your engine. For additional guidance, our expert support team is available to assist.

7. What are signs that my MG521 transmission needs maintenance?

Look for fluid leaks, slipping gears, overheating, unusual noises, or reduced performance.

8. Do you offer technical support?

Absolutely! Our knowledgeable team is available to provide expert advice, troubleshooting support, and installation guidance.

9. Can I purchase parts for other Twin Disc transmissions?

Yes! We offer a wide selection of parts for other Twin Disc models, all available through our online store.

10. How do I place an order?

Visit our website, browse the MG521 parts catalog, select your items, and complete your order online. Contact us if you have any questions.

Order Twin Disc MG521 Parts Today

Choose Diesel Pro Power as your trusted supplier of Twin Disc MG521 marine transmission parts. With fast shipping, expert support, and quality you can rely on, we make it easy to keep your MG521 running smoothly.

Explore our catalog today and place your order with confidence. For assistance, contact us at 888-433-4735 (US) or 305-545-5588 (International) during business hours (8 a.m. to 5 p.m. EST, Monday–Friday).

Marine Transmission Specifications & Applications of the Twin Disc MG521

Overview of the Twin Disc MG521 Marine Transmission

The Twin Disc MG521 is a high-capacity marine transmission built for continuous-duty performance in offshore, commercial fishing, towing, and industrial marine operations. Designed for reliability and torque stability under demanding workloads, the MG521 is an evolution of Twin Disc’s trusted geartrain architecture—offering enhanced reduction ratios, heavy-duty internal components, and dependable hydraulic clutch engagement.

Its compatibility with high-horsepower diesel engines and optional power take-off (PTO) systems makes it a preferred solution for operators running workboats, trawlers, dredgers, and supply vessels. The MG521 can be configured for straight or down-angle installations, providing installation flexibility for a range of hull types and engine room layouts.

Key Specifications of the Twin Disc MG521

Type: Heavy-duty marine transmission with oil-cooled hydraulic clutch
Horsepower Rating (Approximate):

Continuous Duty: Up to 1,000 HP @ 1800 RPM
Intermittent Duty: Up to 1,200 HP @ 2300 RPM

Maximum Input Speed: 2500 RPM
Reduction Ratios Available:

2.00:1
2.50:1
3.00:1
3.50:1
4.00:1
4.50:1

Input Housing: SAE No. 0 or SAE No. 1
Flywheel Compatibility: 18", 14"
Clutch Type: Hydraulically actuated multi-disc, oil-cooled
Cooling System: Oil-to-water heat exchanger standard
Lubrication System: Pressure lubrication with internal oil pump
Oil Capacity: Approximately 24–30 quarts
Dry Weight: Approximately 1,600–1,900 lbs depending on ratio and configuration
Mounting Options: Straight or 8° down-angle output
Rotation Compatibility: Bi-directional input for LH or RH engines
Optional Features:

Hydraulic or mechanical PTO
Trolling valve
Flexible or rigid engine mounts
Electronic shift controls

Common Marine Applications for the MG521

The MG521 is engineered for rugged, continuous-duty operation and is frequently found in:

Tugboats and Pushboats: Where high bollard pull and torque are needed for prolonged propulsion tasks
Commercial Fishing Vessels: Ideal for deep-sea trawlers, seiners, and longliners operating long hours offshore
Offshore Support Vessels (OSVs): Delivers stable, high-load propulsion for vessels servicing oil rigs and platforms
Dredging and Mining Support Craft: With strong PTO compatibility for hydraulic pumps and support equipment
Harbor Utility and Workboats: Provides durable performance in towing, line handling, and cargo transport roles

Most Common Engine Models Paired with the Twin Disc MG521

Designed to support engines producing 800 to 1,200 horsepower, the MG521 is compatible with a range of commercial diesel engines used in marine propulsion:

Cummins Marine Engines

Cummins KTA38-M
Cummins QSK38 (commercial duty ratings)
These Cummins engines match well with the MG521’s torque tolerance and gear reduction options, particularly in trawlers and supply vessels.

Caterpillar Marine Engines

Caterpillar 3412E
Caterpillar C32 (mid-range ratings)
Popular in fishing fleets and offshore supply applications, these Caterpillar platforms pair effectively with MG521 for continuous-duty workloads.

MTU Marine Engines

MTU Series 2000 and 4000 (lower ratings)
Used in high-performance or large-displacement vessels, MTU engines provide high torque that the MG521 is built to manage reliably.

Detroit Diesel Marine Engines

Detroit Diesel 16V92
Detroit Diesel 16V149
The MG521 is frequently used in vessel repowers or refits where these legacy high-horsepower Detroit engines are still in service.

Advantages of the Twin Disc MG521

High Torque Capacity: Built for marine applications requiring constant power delivery under heavy load
Wide Ratio Selection: Allows for tailored propulsion performance across vessel types
Efficient Clutch Engagement: Hydraulic clutch system ensures minimal wear and smoother transitions
Durable Internal Architecture: Forged gears and precision-machined shafts for long service life
Flexible Configuration: Available in both straight and down-angle outputs to suit new and existing installations

Ideal Use Cases for the MG521

Vessel Type	MG521 Suitability	Notes
Tugboats (Harbor & River)	Excellent	Delivers required torque for heavy push/pull ops
Offshore Supply Vessels	Excellent	High-load geartrain matches OSV mission profiles
Deep-Sea Fishing Vessels	Excellent	Withstands hours of propulsion with variable load
Dredging and Support Craft	Excellent	Strong PTO pairing for auxiliary hydraulic systems
Passenger Ferries and Yachts	Not Ideal	Overpowered for light-duty, high-speed recreational use