V-Belt (A-31) – Fits Yanmar 1GM, 2GM, 3GM, 3HM (Replaces 128670-77350, 18-15407)
V-Belt (A-31) – Fits Yanmar 1GM, 2GM, 3GM, 3HM (Replaces 128670-77350, 18-15407) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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V-Belt (A-31) – Fits Yanmar 1GM, 2GM, 3GM, 3HM (Replaces 128670-773...
V-Belt (A-31) – Fits Yanmar 1GM, 2GM, 3GM, 3HM (Replaces 128670-77350, 18-15407) is backordered and will ship as soon as it is back in stock.
Product Details
This V-Belt (A-31) – Fits Yanmar 1GM, 2GM, 3GM, 3HM Series Marine Engines is engineered for Yanmar marine diesel engines, including 9–30 HP, 4-stroke variants manufactured from approximately 1980 onwards. It serves as a crucial component for driving the alternator or generator.
This part is a direct replacement for Yanmar part number 128670-77350 and Sierra 18-15407.
- Designed for direct, hassle-free installation.
- Constructed from synthetic rubber with fiber reinforcement for durability.
- Functions as the primary alternator/generator drive belt.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yanmar | 128670-77350 |
| Sierra | 18-15407 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This V-belt is designed for a wide range of Yanmar marine diesel engines from the GM and HM series.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Yanmar | 1GMYS-C | 9 | 4-Stroke | 128670-77350 | |
| Yanmar | 1GMYS-EC | 9 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GMYE-EC | 13 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GMLP | 13 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GM20 | 18 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GM20C | 18 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GM20F | 18 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GM20-YEU | 18 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GM20FV | 18 | 4-Stroke | 128670-77350 | |
| Yanmar | 2GM20VE | 18 | 4-Stroke | 128670-77350 | |
| Yanmar | 3GM30 | 24-27 | 4-Stroke | 128670-77350 | |
| Yanmar | 3GM30C | 24-27 | 4-Stroke | 128670-77350 | |
| Yanmar | 3GM30F | 24-27 | 4-Stroke | 128670-77350 | |
| Yanmar | 3GM30-YEU | 24-27 | 4-Stroke | 128670-77350 | |
| Yanmar | 3GM30VE | 24-27 | 4-Stroke | 128670-77350 | |
| Yanmar | 3GMD | 24-27 | 4-Stroke | 128670-77350 | |
| Yanmar | 3HM | 30 | 4-Stroke | 128670-77350 | |
| Yanmar | 3HMF | 30 | 4-Stroke | 128670-77350 | |
| Yanmar | 3HM35 | 30 | 4-Stroke | 128670-77350 | |
| Yanmar | 3HM35F | 30 | 4-Stroke | 128670-77350 |
Technical Specs
- Product Type
- V-Belt (A-31)
- Installation
- Direct replacement
- Fuel Type
- Diesel
- Connection
- N/A - Belt Drive
- Housing Material
- Synthetic rubber with fiber reinforcement
- Housing Color
- Black
- Dimensions
- A-31 profile, approx. 31 inches circumference
- Fitting Type
- V-groove pulley system
- Other Technical Attributes
- Alternator/generator drive belt
- Warranty
- Varies by retailer (6-12 months typical)
What’s in the Box
- 1 x V-Belt (128670-77350)
Installation Notes
- Ensure the engine is off and cool, and disconnect the battery for safety.
- Locate the existing V-belt and identify the tensioner pulley.
- Loosen the tensioner to slacken the old belt.
- Carefully remove the old belt from the pulleys, noting its routing path.
- Compare the old belt with the new one to confirm identical length and profile.
- Route the new belt over the pulleys, following the correct path.
- Apply tension to the new belt according to your engine's service manual specifications (typically about 1/2 inch of deflection).
- Tighten the tensioner and any other loosened bolts.
- Reconnect the battery, start the engine, and visually inspect the belt to ensure it is tracking correctly.
Troubleshooting & FAQ
How do I know if this V-belt will fit my engine?
This belt is designed for Yanmar 1GM, 2GM, 3GM, and 3HM series engines. The most reliable way to confirm fitment is to check the engine compatibility table on this page and match your specific model number. You can also cross-reference the OEM part number 128670-77350 with your old belt or service manual.
What are the common signs of a failing V-belt?
Symptoms of a worn or failing V-belt include high-pitched squealing noises (especially on startup), visible cracks or fraying on the belt's surface, a glazed or shiny appearance on the sides, and inconsistent alternator charging or engine cooling performance.
How often should I inspect or replace my engine’s V-belt?
Regular inspection during routine engine checks is recommended. Look for signs of wear, damage, or improper tension. While there is no universal replacement interval, a general guideline is to replace the belt every 2-3 years or as specified in your Yanmar engine's maintenance schedule, whichever comes first.
What’s the difference between this belt and the original Yanmar OEM part?
This aftermarket belt is manufactured to meet or exceed original equipment manufacturer (OEM) specifications for fit, form, and function. It is made from comparable high-quality materials (fiber-reinforced synthetic rubber) to ensure reliable performance and durability, but at a more competitive price point.
Can I install this V-belt myself?
Yes, replacing a V-belt is a common maintenance task for experienced boat owners. However, it requires correctly loosening and retightening the tensioner to achieve the proper belt tension. If you are unfamiliar with this process, professional installation is recommended to prevent damage to the belt or engine components.
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