Alternator Belt – Fits Yanmar 2GM20F, 3GM30F Marine Engines (Replaces 25132-003700)

Alternator Belt – Fits Yanmar 2GM20F, 3GM30F Marine Engines (Replaces 25132-003700)

This high-quality V-belt is designed for Yanmar 2GM20F and 3GM30F series marine diesel engines. It is suitable for both fresh water cooled and heat exchanger cooled models, including the standard and YEU (European-manufactured) variants.

This belt is a direct replacement for Yanmar part numbers 25132-003700, 25132-003700E, and 124732-42290, ensuring a precise fit and reliable performance for your engine's alternator system.

• Belt Profile: A37 (940 mm / 37 inches)
• Material: Durable Neoprene with high-strength Polyester Cord reinforcement.
• Package Includes: 1 x Alternator V-Belt

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 Alternator Belt (Replaces OEM Part 25132-003700)

Installation Guide

1. Ensure the engine is turned off and cooled completely.
2. Disconnect the battery to prevent accidental starting.
3. Loosen the alternator pivot bolt just enough to allow slight movement. Also loosen any adjuster-plate or tensioner bolts.
4. Identify the belt routing around the crankshaft, water-pump, and alternator pulleys.
5. Remove the old belt by swiveling the alternator or tensioner to relieve tension, then slip the belt off the pulleys.
6. Inspect pulley grooves for wear, rust, or corrosion. Clean them thoroughly if needed.
7. Route the new belt following the same pulley path. Ensure it seats properly in all V-grooves.
8. Tension the belt: A correctly tensioned belt should deflect about 1 cm (½″) under moderate thumb pressure on the longest span.
9. Tighten all bolts: Secure the adjuster-plate bolt first, then the main pivot bolt to factory torque specifications.
10. Reconnect the battery.
11. Start the engine and observe belt tracking to ensure it's centered in the grooves and running smoothly.
12. Shut down the engine and recheck the tension after a short run-in period. Re-tension if necessary.

Troubleshooting & FAQ

How do I confirm this belt fits my Yanmar engine?
This belt is designed for the Yanmar 2GM20F and 3GM30F series, including F and F-YEU variants. Please check the "Compatible Engine Models" table to verify your specific model. It directly replaces OEM part number 25132-003700.

What is the correct tension for this V-belt?
Proper tension is critical for performance and longevity. A correctly tensioned V-belt will deflect approximately 1 cm (½ inch) when you apply moderate thumb pressure to the middle of the longest span between pulleys.

Are there other recommended aftermarket belts?
Yes, some boaters have reported good results with Gates 6463MC (noted for reduced dust) and Mitsubishi REMF6370 as compatible alternatives.

How often should I replace my alternator belt?
It is best practice to inspect your belt annually for signs of cracking, fraying, glazing, or excessive wear. We recommend replacing it as part of your regular maintenance schedule or immediately if any damage is found. Many mariners carry a spare onboard as a precaution.

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.