April 8, 2025
Pre-Installation Checklist for Allison M & MH Marine Transmissions
1. Confirm Model Compatibility
2. Inspect the Transmission
3. Gather Necessary Tools and Materials
4. Prepare the Workspace
Mounting Procedures for Allison M & MH Marine Transmissions
1. Lifting the Transmission
2. Engine Coupling
3. Mounting the Transmission
4. Foot Mount Adjustments (if applicable)
Alignment With Engine and Shaft for Allison M & MH Marine Transmissions
1. Initial Engine-to-Transmission Alignment
2. Propeller Shaft Alignment
3. Confirming Parallelism and Angular Alignment
4. Final Tightening
Fastener Torque Specifications for Allison M & MH Marine Transmissions
Bell Housing Bolts (Grade 8 Bolts)
Output Coupling Bolts
Transmission Mounting Bolts to Base
Oil Pan or Filt
er Housing Bolts
Sealing Surfaces and Gasket Preparation for Allison M & MH Marine Transmissions
1. Clean All Sealing Surfaces
2. Inspect for Damage
3. Selecting Gaskets and Sealants
4. Sealing Threaded Connections
5. Oil Seals and Shaft Seals
6. Leak Testing
Final Notes on Installation for Allison M & MH Marine Transmissions
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April 8, 2025
Physical Dimensions
Allison M Series Dimensions
Allison MH Series Dimensions
Weight
Allison M Series Weight Specifications
Allison MH Series Weight Specifications
Input/Output Shaft Specifications
Allison M Series Input/Output Shaft Details
Input Shaft:
Output Shaft:
Allison MH Series Input/Output Shaft Details
Input Shaft:
Output Shaft:
Rotation Direction and Gear Ratios
Rotation Direction
Gear Ratios
How to choose the right ratio:
Torque Handling and Horsepower Limits
Allison M Series Capabilities
Allison MH Series Capabilities
Final Notes on Specification Use
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April 8, 2025
Overview of Allison M & MH Series in Marine Applications
Legacy, Reliability, and Usage in Commercial and Recreational Vessels
A Legacy Built on Performance
Trusted in Commercial Marine Operations
Proven in Recreational and Private Yachts
Reliability and Longevity
Why Proper Servicing Matters: Performance, Longevity, and Safety
Performance Depends on Preventive Maintenance
Longevity Through Scheduled Maintenance
Safety Implications of Transmission Neglect
Cost Savings and Operational Continuity
Final Word on the Importance of This Guide
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April 8, 2025
Why Diesel Pro Power?
Shop Allison Marine Gear and Parts
Allison Marine M General Information
Allison Marine MH General Information
Bearing Maintenance and Repair
Hydraulic Pump System
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April 7, 2025
1. What type of oil should I use in the Twin Disc MG521?
2. How much oil does the MG521 hold?
3. How often should I change the oil?
4. How often should I change the oil filter?
5. What is the correct operating oil pressure?
6. What causes delayed engagement in gear?
7. How do I bleed air from the control system?
8. Can I run the MG521 dry without oil?
9. What are signs my clutch plates need replacement?
10. How do I inspect the clutch plates?
11. How do I know if my bearings are bad?
12. What’s the difference between forward and reverse clutch plates?
13. Are Diesel Pro Power’s clutch plates interchangeable with OEM?
14. How often should I check alignment?
15. What causes excessive vibration in the MG521?
16. How tight should mounting bolts be torqued?
17. Can I install the MG521 vertically?
18. Is there a filter inside the MG521?
19. How do I prime the MG521 after rebuilding?
20. Can I use synthetic oil in the MG521?
21. What are common signs of oil contamination?
22. What should I do if my MG521 overheats?
23. What are acceptable gear backlash values?
24. How do I measure gear backlash?
25. What causes noisy operation?
26. Can I operate the MG521 with a damaged output seal?
27. What’s included in a standard rebuild kit?
28. Does Diesel Pro Power offer technical support for installations?
29. Can I use aftermarket bearings in the MG521?
30. How do I disconnect the output flange?
31. What tools are required for MG521 disassembly?
32. What’s the weight of the MG521?
33. Can I install the MG521 without alignment tools?
34. How do I recheck alignment after installation?
35. Should I replace the flexible coupling during a rebuild?
36. What causes the MG521 to slip in forward but not reverse?
37. Is there a rebuild video available?
38. What is the difference between a plate kit and a rebuild kit?
39. Should I resurface the gear teeth if worn?
40. Do I need to remove the engine to service the MG521?
41. What if I can’t identify my MG521 model?
42. Are MG521 rebuild kits in stock?
43. What is the warranty on Diesel Pro’s MG521 parts?
44. Can I order individual parts instead of a full kit?
45. What’s the lead time for international orders?
46. Can I rebuild my MG521 on the vessel?
47. What’s the best way to clean old clutch debris?
48. What’s the typical lifespan of a rebuilt MG521?
49. Can the MG521 be upgraded with newer control systems?
50. Where can I buy MG521 parts online?
Videos About Twin Disc Transmissions
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April 7, 2025
Overview of Rebuild Kits Available For Twin Disc MG521
1. Basic Service Kit
2. Standard Rebuild Kit
3. Master Overhaul Kit
Comparison to OEM Parts
OEM Pros:
OEM Cons:
Diesel Pro Aftermarket Pros:
Aftermarket Misconceptions:
Diesel Pro Power Aftermarket Kits With OEM Matching Warranty
What the Warranty Covers:
Support You Can Trust
Contents of Standard Rebuild Kits For MG521
1. Clutch Plate Kit
2. Bearing Set
3. Gasket & Seal Set
4. Snap Rings and Washers
5. Oil Filter
6. Hardware (in Master Kits)
Plate Kits, Gasket Kits, Seal Kits, and Bearings
Clutch Plate Kits
Gasket Kits
Seal Kits
Bearing Kits
When to Replace Full Assemblies vs. Individual Parts
Replace Individual Parts If:
Replace Full Assemblies If:
Lead Times, Support, and Ordering From Diesel Pro
1. Lead Times
2. Shipping Options
3. How to Order
Conclusion: Rebuilding With Confidence and Clarity
Videos About Twin Disc Transmissions
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Free US Calls: 1-888-433-4735
International: 305-545-5588
