V-Belt – Fits Yanmar 4LH & 4LHA Series Marine Engines (Replaces 121850-42280E, 121850-42280)

V-Belt – Fits Yanmar 4LH & 4LHA Series Marine Engines (Replaces 121850-42280E)

This V-belt is a direct replacement for the alternator drive belt on Yanmar 4-cylinder 4LH and 4LHA series fresh-water cooled inboard marine diesel engines. It is engineered from fiber-reinforced rubber to meet or exceed OEM specifications for durability and performance.

This belt replaces Yanmar part numbers 121850-42280E and 121850-42280, as well as the MITSUBOSHI part number RECMF-6460, which is often printed on the original belt.

• Function: Drives the fresh water pump and alternator.
• Material: Constructed from durable, fiber-reinforced rubber for reliable power transmission.
• Installation: Designed for a precise fit on specified Yanmar engine models.

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 121850-42280E / 121850-42280)

Installation Guide

1. Ensure the engine is turned off and has cooled down completely. Disconnect the battery to prevent accidental starting.
2. Loosen the alternator pivot bolt and any adjuster-plate or tensioner bolts just enough to allow movement.
3. Take note of the existing belt's path around all pulleys (crankshaft, water pump, alternator).
4. Relieve tension by swiveling the alternator or tensioner, then carefully slip the old belt off the pulleys.
5. Inspect pulley grooves for wear, rust, or debris. Clean them thoroughly with a wire brush if necessary.
6. Route the new belt following the same path, ensuring it is properly seated in all V-grooves.
7. Tension the new belt: Pry or swivel the alternator away from the engine to apply tension. A correctly tensioned V-belt should deflect about 1 cm (½″) under moderate thumb pressure on its longest span.
8. Securely tighten all bolts, starting with the adjuster bolt and then the main pivot bolt, to factory torque specifications.
9. Reconnect the battery.
10. Start the engine and briefly run it, watching to ensure the belt tracks centrally in the pulley grooves and runs smoothly.
11. Shut down the engine and re-check the belt tension. New belts may stretch slightly after the initial run-in, so re-tension if needed.

Troubleshooting & FAQ

Q: How do I confirm this V-belt will fit my Yanmar engine?
A: This belt is designed for Yanmar 4LH and 4LHA series engines. Please check the "Compatible Engine Models" table on this page to confirm your specific model is listed. Verifying your original part number against our cross-reference list (121850-42280E, 121850-42280) is the best way to guarantee a match.

Q: What is the correct way to tension this V-belt?
A: Proper tension is critical. On the longest span of the belt between two pulleys, apply moderate thumb pressure. The belt should deflect approximately 1 cm (½ inch). Over-tightening can cause premature wear on the belt and engine bearings, while under-tightening can lead to slipping, squealing, and poor alternator/water pump performance.

Q: My new belt has "MITSUBOSHI - RECMF-6460" printed on it. Is it the right part?
A: Yes. MITSUBOSHI is a common manufacturer for these belts, and RECMF-6460 is an equivalent part number for the Yanmar 121850-42280E. This is a direct replacement.

Q: What are the signs that my V-belt needs replacing?
A: Common signs of a failing V-belt include visible cracks, glazing (shiny surface), fraying edges, or chunking (missing pieces). You may also hear a persistent squealing noise upon startup or during operation, or notice battery charging issues, which could indicate the belt is slipping.

Q: OEM vs. Aftermarket?
A: 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.

Q: How fast do you ship and how much does it cost?
A: 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.

Q: What is your warranty and return policy?
A: 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.