Alternator V-Belt – Fits Yanmar 3JH2, 3JH3, 3JH4E Marine Diesel Series (Replaces 129940-42310, 129940-42310E)

Alternator V-Belt – Fits Yanmar 3JH2, 3JH3, 3JH4E Marine Diesel Series

This high-quality aftermarket V-belt is engineered for Yanmar marine diesel engines, specifically fitting models in the 3JH series. It serves as a direct replacement for multiple OEM part numbers, ensuring reliable performance for your alternator system.

This belt is a direct replacement for Yanmar part numbers 129940-42310, 129940-42310E, 171087-42280, and 25152-004400.

• Installation Method: Direct replacement for a straightforward fit.
• Belt Type: Toothed V-Belt for improved flexibility and grip.
• Quality Standard: Meets OEM quality specifications for dependable operation.

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 V-Belt (Replaces 129940-42310 / 129940-42310E)

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. Note the path 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 to bare metal if needed.
7. Route the new belt following the same pulley path. Ensure it seats properly in all V-grooves.
8. Tension the belt: Swivel the alternator away from the engine to create proper tension. A correctly tensioned V-belt should deflect about 1 cm (½″) under moderate thumb pressure on the longest span.
9. Tighten all bolts: Secure the adjuster-plate bolt, 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 tension after a short run-in period, as new belts may stretch slightly. Re-tension if necessary.

Troubleshooting & FAQ

How do I confirm this V-belt fits my Yanmar engine?
This belt is designed for the Yanmar 3JH series, including models like the 3JH2, 3JH3, and 3JH4E. To ensure compatibility, please check the "Compatible Engine Models" table on this page to verify your specific model is listed. You should also compare the part number 129940-42310 to your existing belt or service manual.

What are the signs of a failing alternator V-belt?
Common signs include visible cracks, fraying, or a glazed, shiny appearance on the belt's surface. You might also hear a high-pitched squealing sound from the engine, especially on startup or when under load. Dimming lights or a battery warning light can also indicate the alternator isn't being driven properly by a slipping belt.

How often should I inspect or replace my V-belt?
It is best practice to inspect your V-belt during regular engine maintenance checks for cracks, wear, and proper tension. While there is no universal replacement interval, they typically last for several hundred hours of use. Replace it immediately if you see any signs of significant wear or damage to avoid 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.