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Introduction
The Twin Disc MG518 Marine Gear is a widely used marine transmission system, known for its high efficiency, reliability, and durability in various marine applications. Understanding its specifications, lubrication requirements, torque specifications, and compatible fluids and materials is essential for proper operation and maintenance.
This guide provides an in-depth look into the Twin Disc MG518 Marine Gear’s technical specifications, including its weight, dimensions, fluid capacity, torque values, and recommended lubricants and compatible materials.
Parts Catalog for Twin Disc MG518 Marine Transmissions
Rebuilt Twin Disc MG518 Marine Transmissions
Plate Kit For Twin Disc MG518 Marine Transmission
Gasket Kits For Twin Disc MG518 Marine Transmission
Technical Specifications for Twin Disc MG518 Marine Gear
Weight and Dimensions
The Twin Disc MG518 Marine Gear is a compact yet heavy-duty marine transmission designed to handle high torque loads in commercial and recreational vessels. The weight and dimensions of this transmission vary slightly depending on the gear ratio and specific model variations. Below are general specifications for the MG518 model:
| Specification | Details |
| Dry Weight | Approx. 350-400 lbs (158-181 kg) |
| Length | Varies based on configuration (typically 20-25 inches long) |
| Width | Approximately 18-22 inches |
| Height | Around 15-18 inches, depending on mounting |
| Input Shaft Diameter | Varies based on the engine coupling |
| Output Shaft Diameter | Standard marine coupling output |
Gear Ratios and Capacity
The MG518 marine gear is available with multiple gear ratios to accommodate different vessel requirements. The gear ratio selection affects the propeller speed, torque delivery, and overall efficiency.
| Gear Ratio | Application | Torque Capacity (lb-ft/Nm) |
| 2.00:1 | General marine applications | 800-1,200 lb-ft (1,085-1,627 Nm) |
| 2.50:1 | Workboats, tugs, and high-load vessels | 1,000-1,400 lb-ft (1,356-1,897 Nm) |
| 3.00:1 | Heavy-duty commercial use | 1,200-1,600 lb-ft (1,627-2,170 Nm) |
The higher the ratio, the lower the propeller speed but with an increase in torque to handle heavier loads. The Twin Disc MG518 is designed to work seamlessly with various marine diesel engines to optimize fuel efficiency and thrust output.
Operating Temperatures and Fluid Capacity
Proper lubrication and cooling are essential to the performance and longevity of the MG518 Marine Gear. The operating temperature range and fluid capacity play a crucial role in keeping the transmission in optimal condition.
| Specification | Value |
| Operating Temperature Range | 180°F – 220°F (82°C – 104°C) |
| Fluid Capacity | 3.5 – 5 quarts (3.3 – 4.7 liters) |
| Oil Cooler Type | Integrated heat exchanger (water-cooled or air-cooled) |
Lubrication Requirements for Twin Disc MG518 Marine Gear
Importance of Proper Lubrication
Lubrication is critical for reducing wear and tear, dissipating heat, and ensuring smooth gear operation. Proper lubricant selection and maintenance prevent premature failure and extend the lifespan of the Twin Disc MG518.
Recommended Lubricants
Twin Disc recommends high-quality transmission fluids that meet or exceed the required viscosity and thermal stability standards. Below are the preferred lubricants for the MG518 marine gear:
| Lubricant Type | Viscosity Grade | Recommended Brand Examples |
| Automatic Transmission Fluid (ATF) | Dexron III / Mercon V | Mobil ATF, Valvoline ATF, Chevron ATF |
| Marine Gear Oil | SAE 30 / SAE 40 (non-detergent) | Shell Rotella, Chevron Delo, Castrol HD |
| Synthetic Oil (Optional for High Loads) | SAE 75W-90 | Mobil 1 Synthetic, Amsoil Marine Gear Lube |
Note: Always refer to the latest manufacturer specifications for recommended lubricants.
Lubrication Maintenance Schedule
| Maintenance Task | Interval |
| Check Oil Level | Every 50 hours or weekly |
| Inspect Oil for Contaminants | Every 100 hours |
| Replace Oil and Filter | Every 500 hours or annually |
| Flush Transmission System | Every 2,000 hours or major overhaul |
How to Change the Oil on the MG518 Marine Gear
- Warm up the transmission to operating temperature.
- Shut down the engine and allow it to cool slightly.
- Drain old oil from the drain plug at the bottom of the transmission.
- Replace the oil filter with a new OEM or equivalent filter.
- Refill with new transmission fluid to the recommended level.
- Run the engine and check for leaks or pressure abnormalities.
Torque Specifications for Twin Disc MG518 Marine Gear
Proper torque values are crucial for preventing fastener loosening, component misalignment, and transmission failure. Below are the recommended torque settings for key components.
Torque Values for Key Components
| Component | Torque Specification (lb-ft/Nm) |
| Bellhousing Bolts | 75-90 lb-ft (102-122 Nm) |
| Output Flange Bolts | 60-80 lb-ft (81-108 Nm) |
| Input Shaft Retaining Nut | 140-180 lb-ft (190-244 Nm) |
| Mounting Bracket Bolts | 50-70 lb-ft (68-95 Nm) |
| Drain Plug | 20-25 lb-ft (27-34 Nm) |
Torque Application Tips
- Use a calibrated torque wrench to achieve the correct values.
- Apply thread locker on critical bolts to prevent loosening under vibration.
- Retorque fasteners after initial break-in (typically after 50 hours of operation).
Compatible Fluids and Materials for Twin Disc MG518 Marine Gear
Selecting the right fluids and materials ensures optimal performance and longevity of the MG518 Marine Gear.
Compatible Transmission Fluids
The MG518 is designed to use a variety of high-performance lubricants, but not all oils are suitable. Below are the approved transmission fluids:
- Dexron III or Mercon ATF (recommended for light to medium-duty applications).
- SAE 30 or SAE 40 Non-Detergent Marine Oil (for heavy-duty applications).
- Synthetic 75W-90 Gear Oil (for extreme operating conditions).
Incompatible Fluids
Avoid using the following, as they can damage seals, cause overheating, or degrade performance:
- Engine oils with high detergent content (can cause foam and heat buildup).
- Hydraulic oils not rated for marine gear use.
- Brake fluid or non-specified synthetic blends.
Recommended Seal and Gasket Materials
The Twin Disc MG518 uses high-durability seals and gaskets to prevent leaks and ensure long-term reliability. Below are the best materials:
- Viton Seals – Excellent for high temperatures and oil resistance.
- Nitrile Rubber Gaskets – Good for moderate temperatures and oil contact.
- Copper Crush Washers – Used in high-pressure sealing applications.
Conclusion
The Twin Disc MG518 Marine Gear is a high-performance transmission designed for demanding marine applications. Understanding its technical specifications, lubrication requirements, torque values, and fluid compatibility is essential for optimal performance and longevity.
By following the correct maintenance procedures and using approved lubricants and fasteners, vessel operators can ensure reliability and efficiency in all conditions.
Parts Catalog for Twin Disc MG518 Marine Transmissions
Rebuilt Twin Disc MG518 Marine Transmissions
Plate Kit For Twin Disc MG518 Marine Transmission
Gasket Kits For Twin Disc MG518 Marine Transmission
