Serpentine Belt Idler Pulley – Fits MerCruiser 4.3, 5.0, 5.7, 6.2L V6/V8 Engines (Replaces 864625T)

Serpentine Belt Idler Pulley – Fits MerCruiser 4.3, 5.0, 5.7, 6.2L V6/V8 Engines

This serpentine belt idler pulley is designed for a wide range of Mercury MerCruiser V6 and V8 engines, including 4.3L, 5.0L, 5.7L, and 6.2L models in both stern drive and inboard configurations. It serves as a direct, reliable replacement for worn or damaged original pulleys.

This component is a direct replacement for the following OEM and aftermarket part numbers: Mercury/MerCruiser 864625T, 807757T, and Sierra 18-6457.

• Engineered for a direct fit, simplifying installation.
• Restores proper serpentine belt tension and alignment.
• Includes one idler pulley assembly.

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. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Idler Pulley (864625T)

Installation Guide

1. Safety First: Disconnect the boat's battery before beginning any work.
2. Relieve Belt Tension: Use a breaker bar or belt tensioner tool to release the tension on the serpentine belt.
3. Remove the Belt: Carefully slide the serpentine belt off the idler pulley and other accessory pulleys.
4. Unbolt the Old Pulley: Use a socket wrench to remove the mounting bolt holding the old idler pulley in place.
5. Clean Mounting Surface: Wipe down the mounting bracket to ensure it is free of dirt and corrosion.
6. Install the New Pulley: Position the new idler pulley and tighten the mounting bolt to the manufacturer's recommended torque specification.
7. Reinstall the Belt: Route the serpentine belt according to your engine's diagram. Ensure it is seated correctly on all pulleys.
8. Apply Tension: Slowly release the tensioner to apply pressure to the newly installed belt.
9. Final Check: Verify the belt is properly aligned and has the correct tension. Reconnect the battery and start the engine to check for proper operation.

Troubleshooting & FAQ

How do I confirm this fits my engine?
First, check your engine model against the "Compatible Engine Models" table. Second, cross-reference your existing part number with the numbers listed in the "Part Number Cross-Reference" section to ensure it is a direct replacement for 864625T, 807757T, or 18-6457.

What are the signs of a failing idler pulley?
Common symptoms include a persistent squeaking, chirping, or grinding sound from the engine bay, visible wobble or play in the pulley, or a serpentine belt that repeatedly slips or appears loose.

How often should I replace the idler pulley?
It is best practice to inspect the idler pulley whenever you service the serpentine belt. We recommend replacing it if it shows any signs of wear, damage, or noise, or as a preventative measure during a complete serpentine belt system overhaul.

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.