Idler Pulley – Fits Mercury Marine/MerCruiser GM V6 V8 Engines (Replaces 807757T)

This replacement idler pulley is designed for late-model GM V6 and V8 sterndrive or inboard engines equipped with serpentine belt systems, typically from 1996 to 2006. It ensures proper belt tension and routing for optimal engine performance, fitting a wide range of popular MerCruiser models including the 4.3L, 5.0L, 5.7L, 6.2L, and 8.1L series.

As a direct replacement part, this pulley matches the fit and function of Mercury/MerCruiser 807757T and Sierra Marine 18-6457, providing a reliable and cost-effective solution for engine maintenance and repair.

• Durable Construction: Made from high-strength thermal resin to withstand engine bay heat and resist corrosion.
• Precise Fit: Engineered with a 6-groove design for 13/16"" (20.6 mm) wide serpentine belts, ensuring secure alignment.
• Ready to Install: Mounts directly to the engine block as a replacement for the original idler pulley.

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 × Idler Pulley (Replaces 807757T)

Explosion Diagram

Installation Guide

1. Ensure the engine is off and cool. Disconnect the battery for safety.
2. Locate the serpentine belt routing diagram on your engine or in your service manual for reference.
3. Use the appropriate tool (usually a breaker bar or ratchet) to release tension from the belt tensioner.
4. Carefully remove the serpentine belt from the idler pulley assembly.
5. Unbolt and remove the old idler pulley using the correct socket.
6. Clean the mounting surface on the engine block to ensure a flat, secure contact for the new pulley.
7. Position the new idler pulley and hand-tighten the mounting bolts.
8. Torque the bolts to manufacturer specifications to prevent them from loosening.
9. Reroute the serpentine belt, making sure it is correctly seated in the grooves of all pulleys.
10. Slowly apply tension back to the system and double-check that the belt alignment is correct.
11. Reconnect the battery and start the engine.
12. Visually inspect the new pulley and belt for any wobble, unusual noises, or vibrations during operation.

Troubleshooting & FAQ

How do I know if this idler pulley fits my MerCruiser engine?
This pulley is designed for late-model (1996-2006) GM-based MerCruiser V6 and V8 engines with a serpentine belt system. Check your engine model against the compatible models list, which includes 4.3L, 5.0L, 5.7L (350), 6.2L, and 8.1L (496) families. The surest way to confirm is by matching your old part number to Mercury 807757T or Sierra 18-6457.

What are common signs of a failing idler pulley?
A worn or failing idler pulley will often produce a high-pitched squealing or grinding noise, especially at idle or during acceleration. You may also notice the serpentine belt slipping, fraying, or showing uneven wear. A visual inspection might reveal wobbling or physical damage like cracks in the pulley.

Is a thermal resin (composite) pulley as durable as a metal one?
Yes. Modern thermal resin composites are specifically engineered for automotive and marine applications. This material is lightweight, corrosion-proof, and highly resistant to the heat cycles found in an engine bay. Many OEM manufacturers use composite pulleys for these reasons, making this an equivalent-quality replacement.

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.