Serpentine Belt Idler Pulley – Fits MerCruiser 4.3, 5.0, 5.7, 6.2L V6/V8 Engines (Replaces 864625T, 807757T)
Serpentine Belt Idler Pulley – Fits MerCruiser 4.3, 5.0, 5.7, 6.2L V6/V8 Engines (Replaces 864625T, 807757T) is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
Serpentine Belt Idler Pulley – Fits MerCruiser 4.3, 5.0, 5.7, 6.2L ...
Serpentine Belt Idler Pulley – Fits MerCruiser 4.3, 5.0, 5.7, 6.2L V6/V8 Engines (Replaces 864625T, 807757T) is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket Serpentine Belt Idler Pulley is designed for a precise fit on a range of Mercury MerCruiser engines, including 4.3L (V6), 5.0L (V8), 5.7L (V8), and 6.2L (V8) models with stern drive or inboard configurations. It ensures proper belt tension and guidance for reliable engine accessory operation.
This component is a direct interchange for Mercury/MerCruiser part numbers 864625T and 807757T, as well as Sierra part number 18-6457.
- Engineered as a direct replacement for a straightforward installation.
- Built to withstand demanding marine environments.
- Includes one high-quality idler pulley.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/MerCruiser | 864625T |
| Mercury/MerCruiser | 807757T |
| Sierra | 18-6457 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This pulley is compatible with the following MerCruiser engines:
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| MerCruiser | 4.3L | 190-220 | 4-Stroke | 864625T | V6 Engine |
| MerCruiser | 5.0L | 220-260 | 4-Stroke | 864625T | V8 Engine |
| MerCruiser | 5.7L | 260-300 | 4-Stroke | 864625T | V8 Engine |
| MerCruiser | 6.2L | 320 | 4-Stroke | 864625T | V8 Engine |
Technical Specs
- Product Type
- Serpentine Belt Idler Pulley
- Installation
- Direct replacement
- Dimensions
- 4.25" diameter (108 mm)
- Weight
- 0.38 lbs (0.17 kg)
- Fitting Type
- Direct mount
What’s in the Box
- 1 x Idler Pulley (864625T)
Installation Notes
- Disconnect the boat's battery for safety.
- Locate the serpentine belt tensioner to relieve tension from the belt.
- Carefully remove the serpentine belt from the old idler pulley.
- Unbolt and remove the old idler pulley from its mounting point.
- Install the new idler pulley, ensuring it is properly seated.
- Tighten the mounting bolt to the manufacturer's recommended torque specification.
- Route the serpentine belt according to your engine's diagram.
- Re-apply tension to the belt using the tensioner.
- Reconnect the battery and start the engine to verify smooth operation and proper belt tracking.
Troubleshooting & FAQ
How do I know if my idler pulley is failing?
Common signs of a worn idler pulley include a persistent squealing, chirping, or grinding noise from the engine bay, visible wobble or play in the pulley, or physical damage like cracks or chips on the pulley surface.
What is the function of the idler pulley?
An idler pulley guides the serpentine belt and helps maintain correct tension as it moves. This ensures accessories like the alternator, water pump, and power steering pump are driven effectively and without slippage.
Is a special tool required for installation?
A standard socket or wrench set is required to remove the mounting bolt. A belt tensioner tool or a long-handled breaker bar may also be needed to release the tension on the serpentine belt, depending on your engine's specific tensioner design.
Does this pulley come with a new bolt?
This package contains the idler pulley only. The original factory mounting bolt is typically reused. Inspect the bolt for corrosion or damage before reinstalling.
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.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
