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

$24.00

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Idler Pulley – Fits Mercury Marine/MerCruiser GM V6 V8 Engines (Replaces 807757T) is backordered and will ship as soon as it is back in stock.

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If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This is a high-quality replacement Idler Pulley – Fits Mercury Marine/MerCruiser GM V6 V8 Engines (Replaces 807757T), engineered for durability and performance. It is designed to fit late-model GM V6 and V8 engines (1996–2006), including MerCruiser 4.3L, 5.0L, 5.7L, 6.2L, and 8.1L sterndrive or inboard models equipped with a serpentine belt system.

This component serves as a direct replacement for Mercury/MerCruiser part number 807757T and Sierra Marine 18-6457, ensuring precise fit and function.

Installation Location: Engine mounted
Housing Material: High-strength thermal resin (composite)
Warranty: 1-year coverage against manufacturing defects

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury/MerCruiser	807757T
Sierra Marine	18-6457

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This pulley is designed for a wide range of MerCruiser engines based on the GM block that utilize a serpentine belt system.

Model	Rated HP	Stroke	Years	OEM Part No.	Notes
4.3L MPI ALPHA/BRAVO	220	4-Stroke	1998–2006	807757T	GM-based engine
350 MAG MPI ALPHA/BRAVO	300	4-Stroke	1998–2006	807757T	GM-based 5.7L engine
350 MAG MPI HORIZON	300	4-Stroke	1998–2006	807757T	GM-based 5.7L engine
5.0L MPI ALPHA/BRAVO	260	4-Stroke	1998–2006	807757T	GM-based engine
5.7L MPI ALPHA/BRAVO	300	4-Stroke	1998–2006	807757T	GM-based engine
5.7L MPI HORIZON	300	4-Stroke	1998–2006	807757T	GM-based engine
6.2L MPI	320	4-Stroke	1998–2006	807757T	GM-based engine
6.2L MPI HORIZON	320	4-Stroke	1998–2006	807757T	GM-based engine
MX 6.2L MPI	320	4-Stroke	1998–2006	807757T	GM-based engine
496 MAG / 8.1L MPI	375-420	4-Stroke	1998–2006	807757T	GM-based engine
520/525/540/565/600/662/700 Series	520-700	4-Stroke	2000–2006	807757T	High-performance models
8.2L MAG	380-430	4-Stroke	2001–2006	807757T	GM-based engine
SCORPION 350/377 (SKI)	330-377	4-Stroke	1999–2006	807757T	Ski/tow sport engines

Technical Specs

Product Type: Serpentine Belt Idler Pulley
Installation: Engine mounted
Housing Material: Thermal resin (composite)
Housing Color: Black
Dimensions: 82.55 mm × 82.55 mm × 28.7 mm (3.25" × 3.25" × 1.13")
Diameter: 76.2 mm (3")
Weight: 0.127 kg (0.28 lbs)
Belt Type: Serpentine
Belt Width: 20.6 mm (13/16")
Groove Design: 6-groove

What’s in the Box

1 × Idler Pulley (807757T)

Installation Notes

Ensure the engine is off and cool. Disconnect the battery for safety.
Locate your engine's serpentine belt routing diagram for reference.
Use the appropriate tool to release tension from the belt tensioner.
Carefully remove the serpentine belt from the idler pulley.
Unbolt and remove the old idler pulley assembly with the correct socket tools.
Thoroughly clean the mounting surface to ensure a secure fit for the new part.
Position the new idler pulley and hand-tighten the mounting bolts.
Torque the bolts to the manufacturer's recommended specifications.
Reroute the serpentine belt according to the diagram.
Re-apply tension to the belt and verify that it is properly aligned on all pulleys.
Reconnect the battery, start the engine, and visually inspect the pulley's operation.
Listen for any unusual noises or vibrations.

Troubleshooting & FAQ

What are the signs of a failing idler pulley?

Common symptoms include a squeaking or rattling noise from the engine bay, visible wobbling of the pulley, excessive resistance or free-spinning when turned by hand (with the belt off), and physical signs of wear like cracks or chips on the pulley surface.

How can I confirm this pulley fits my specific engine model?

This pulley fits a wide range of MerCruiser GM-based engines from 1996–2006 with serpentine belts. The best way to confirm is to cross-reference your original part number with those listed in our Part Number Matrix (807757T) or find your engine family in the compatibility table.

How often should an idler pulley be replaced?

There is no fixed replacement interval. It should be inspected during routine serpentine belt service. We recommend replacing it whenever you replace a worn belt, a tensioner, or if it shows any signs of wear, noise, or damage during inspection.

What is the difference between this pulley and the OEM part?

This is an aftermarket part designed to meet or exceed OEM specifications for fit, form, and function. It is made with comparable high-quality materials (thermal composite) but is available at a more competitive price point.

Do I need special tools for installation?

You will need standard mechanic's tools, including a socket set. A serpentine belt tensioner tool or a long-handled ratchet may be required to release the belt tension safely and effectively.

Is this a 'flat' or 'grooved' idler pulley?

This is a 6-groove pulley, designed for use with a standard serpentine belt. Ensure the grooved side of your belt runs along this pulley.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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