Alternator V-Belt – Fits Yanmar 2GM & 3GM Series Diesel Engines (Replaces 25132-003100)

Alternator V-Belt – Fits Yanmar 2GM & 3GM Series Diesel Engines

This is an aftermarket alternator V-belt designed as a direct replacement for Yanmar marine diesel engines in the 2GM and 3GM series. It is manufactured to meet or exceed OEM specifications, ensuring reliable performance. This crucial component connects the engine crankshaft to the alternator, generating the electrical power necessary for your vessel's systems.

This belt is fully compatible with a wide range of models, including the popular 2GM20, 3GM30, and their related variants. It serves as a direct replacement for multiple Yanmar part numbers, simplifying part selection and maintenance.

• Direct Replacement For: Yanmar 25132-003100, 25132-003000, & 128670-77350
• Material: High-strength synthetic rubber with fiber reinforcement for durability and resistance to heat and oil.
• Belt Profile: A-31

Part Number Cross-Reference

Use this table to confirm equivalent part numbers. This belt is a direct replacement for the following OEM parts.

Compatible Engine Models

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

1 x Alternator V-Belt (Replaces 25132-003100, 25132-003000, 128670-77350)

Installation Guide

1. Safety First: Ensure the engine is completely turned off and has cooled down.
2. Disconnect Power: Disconnect the battery to prevent any accidental starting.
3. Loosen Alternator: Loosen the main alternator pivot bolt and any tensioner bolts just enough to allow the alternator to move.
4. Note Belt Path: Carefully observe the existing belt's path around the crankshaft, alternator, and any other pulleys. Taking a picture can be helpful.
5. Remove Old Belt: Push the alternator towards the engine to create slack, then slip the old belt off the pulleys.
6. Inspect Pulleys: Check all pulley grooves for rust, damage, or wear. Clean them thoroughly before installing the new belt.
7. Route New Belt: Fit the new belt along the correct path, making sure it sits properly in all V-grooves.
8. Tension the Belt: Use a lever to carefully swivel the alternator away from the engine to apply tension. A correctly tensioned belt should have about 1 cm (½″) of deflection when pressed firmly with your thumb on the longest span.
9. Tighten Bolts: While holding tension, tighten the adjuster bolt first, then securely tighten the main pivot bolt to the manufacturer's recommended torque.
10. Reconnect Battery: Re-attach the battery cables.
11. Test Run: Start the engine and watch the belt to ensure it is running true and centered in the pulley grooves.
12. Re-Check Tension: After a brief run time, shut down the engine and re-check the belt tension. New belts may stretch slightly and require a final adjustment.

Troubleshooting & FAQ

How do I confirm this belt fits my Yanmar engine?
First, check the Compatible Engine Models table on this page to find your specific model (e.g., 2GM20, 3GM30). Pay close attention to any notes, such as those regarding serial numbers. The surest way is to cross-reference the part number printed on your old belt with the ones listed here: 25132-003100, 25132-003000, or 128670-77350.

What are the signs of a failing alternator belt?
Common signs include a loud squealing noise from the engine bay, especially on startup or when under load. You may also notice visible cracks, fraying, or a glazed, shiny appearance on the belt's surface. A failing belt can also lead to battery charging problems (dimming lights, dead battery) or engine overheating if it also drives the water pump.

How often should I replace my alternator V-belt?
You should visually inspect your belt during every routine engine check. Look for signs of wear like cracks or glazing. While there is no fixed replacement interval, it is good practice to replace it preventatively every few years or immediately if any signs of damage are found to avoid being stranded by a broken belt.

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.