V-Belt (A-31) - Fits Yanmar 1GM, 2GM, 3GM, 3HM Series Marine Engines (Replaces 128670-77350)

V-Belt (A-31) – Fits Yanmar 1GM, 2GM, 3GM, 3HM Series Marine Engines

This high-quality V-belt is designed for Yanmar marine diesel engines in the 1GM, 2GM, 3GM, and 3HM series, covering models from 9 to 30 HP manufactured from approximately 1980 onwards. It serves as a direct replacement alternator/generator drive belt, ensuring reliable power generation for your vessel's electrical systems.

This part is a direct replacement for Yanmar part number 128670-77350 and Sierra part number 18-15407.

• Installation Type: Direct replacement for a straightforward fit.
• Engine Compatibility: Designed specifically for Yanmar diesel engines.
• Function: Drives the engine's alternator or generator.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

• 1 x V-Belt (Replaces 128670-77350)

Installation Guide

1. Safety First: Ensure the engine is off and cool. Disconnect the boat's battery to prevent accidental starting.
2. Locate the Belt: Identify the V-belt connecting the engine crankshaft pulley to the alternator pulley.
3. Loosen Tension: Find the alternator's pivot bolt and tensioning bolt. Loosen both slightly to allow the alternator to move.
4. Release Tension: Gently push the alternator toward the engine block to create slack in the belt.
5. Remove Old Belt: Carefully slip the old belt off the pulleys. Note its path for correct reinstallation.
6. Install New Belt: Route the new V-belt around the pulleys, ensuring it is properly seated in each V-groove.
7. Apply Tension: Pry the alternator away from the engine to apply tension. The belt is correctly tensioned when you can press it down about 1/2 inch (1.3 cm) at its longest span.
8. Tighten Bolts: While holding tension, securely tighten the tensioning bolt and then the pivot bolt.
9. Final Check: Reconnect the battery, start the engine, and check for proper belt operation and listen for any unusual noises.

Troubleshooting & FAQ

How do I confirm this V-belt fits my engine?
Verify that your engine model is listed in the "Compatible Engine Models" table above. This A-31 V-belt is a direct replacement for Yanmar part number 128670-77350 and fits 1GM, 2GM, 3GM, and 3HM series engines.

What are the signs my current V-belt needs replacement?
Common signs of a worn belt include visible cracks, fraying, glazing (a shiny, smooth surface on the sides), or hardening. You may also hear a loud squealing sound during engine operation or notice reduced performance from your alternator (e.g., dimming lights, low battery voltage).

How often should I replace the V-belt?
There is no fixed replacement interval; it depends on usage and conditions. We recommend inspecting the belt for wear during every routine engine service. Replace it proactively if you see any signs of damage or deterioration to avoid failure at sea.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.