Seawater Pump Drive Belt – Fits Yanmar 1GM, 2GM, 3GM Series (Replaces 104511-78780, 104511-78780E)

Seawater Pump Drive Belt – Fits Yanmar 1GM, 2GM, 3GM Series (Replaces 104511-78780)

This high-quality aftermarket V-belt is engineered to drive the seawater pump on a wide range of Yanmar marine diesel engines. It is a direct-fit replacement for models in the 1GM, 2GM, 3GM, 2YM, and 3YM series, providing a reliable and essential component for your engine's cooling system.

Designed to meet or exceed OEM specifications, this belt ensures proper tension and power transmission from the engine pulley to the raw water pump. It directly replaces Yanmar part numbers 104511-78780 and 104511-78780E, as well as several aftermarket equivalents.

• Fitment: Designed for Yanmar 4-stroke inboard diesel engines, including popular models from the 1980s through the 2000s.
• Function: A critical component that drives the engine's seawater pump for cooling.
• Material: Manufactured from durable materials to match the performance and longevity of the original 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 Seawater Pump Drive Belt (Replaces 104511-78780 / 104511-78780E)

Installation Guide

Professional installation is recommended. Always consult your engine's service manual for detailed instructions.

1. Safety First: Ensure the engine is off and the battery is disconnected to prevent accidental starting.
2. Locate the Belt: Identify the existing seawater pump drive belt on the front of the engine.
3. Release Tension: Loosen the bolts on the alternator or tensioner pulley to create slack in the old belt.
4. Remove Old Belt: Carefully slip the old belt off all pulleys.
5. Install New Belt: Route the new belt around the pulleys, making sure it is correctly seated in each groove.
6. Apply Tension: Adjust the alternator or tensioner back to its original position to apply the correct tension to the new belt. Do not overtighten.
7. Final Check: Tighten all mounting bolts securely. Reconnect the battery and briefly start the engine to verify the belt is running true and without noise.

Troubleshooting & FAQ

How do I confirm this belt fits my Yanmar engine?

This belt is compatible with a wide range of Yanmar engines like the 1GM, 2GM, 3GM, and YM series. The best way to confirm fitment is to check the Compatible Engine Models table on this page and verify that your model is listed. Always cross-reference the OEM part number 104511-78780 with the one specified in your engine's service manual. Pay close attention to any serial number notes for models like the 3YM20 and 3YM30.

What are the signs my drive belt needs to be replaced?

Common symptoms of a worn-out drive belt include visible cracks, fraying, glazing (a shiny appearance), or missing chunks. You might also hear a persistent squealing sound during engine operation or notice your engine temperature creeping up, which could indicate the belt is slipping and not driving the seawater pump effectively.

How often should I inspect or replace this belt?

Preventative maintenance is key. We recommend visually inspecting the belt during every routine engine check. As a general guideline, consider replacing it according to the service interval specified in your Yanmar owner's manual or at the first sign of wear to avoid an unexpected failure.

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.