Aftermarket Serpentine Belt Idler Pulley for MerCruiser and Volvo Penta GM V6 & V8 Engines – Replaces 807757T
Aftermarket Serpentine Belt Idler Pulley for MerCruiser and Volvo Penta GM V6 & V8 Engines – Replaces 807757T is backordered and will ship as soon as it is back in stock.
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Aftermarket Serpentine Belt Idler Pulley for MerCruiser and Volvo P...
Aftermarket Serpentine Belt Idler Pulley for MerCruiser and Volvo Penta GM V6 & V8 Engines – Replaces 807757T is backordered and will ship as soon as it is back in stock.
Product Details
This is an aftermarket serpentine belt idler pulley for selected MerCruiser and Volvo Penta stern-drive or out-drive applications using GM V6 and V8 engines. The pulley is designed for use with a serpentine belt and is listed for 4.3L V6, 5.0L and 5.7L small-block V8, and 8.1L big-block V8 applications.
The composite pulley has a 3-inch outside diameter and is intended for a 13/16-inch-wide serpentine belt. Confirm the original pulley dimensions, belt width, belt routing, engine configuration, and reference number before ordering.
- Product Type: Serpentine belt idler pulley
- Application: MerCruiser and Volvo Penta stern-drive or out-drive systems
- Engine Families: GM 4.3L V6, 5.0L and 5.7L small-block V8, and 8.1L big-block V8
- Pulley Material: Composite
- Pulley Outside Diameter: 3 inches
- Compatible Belt Width: 13/16 inch
Part Number Matrix
Use the following manufacturer and aftermarket references to help compare the replacement pulley with your original part. Reference numbers do not replace application and dimensional verification.
| Brand or Reference | Part Number |
|---|---|
| Mercury/MerCruiser | 807757T |
| Volvo Penta | 3860201 |
| Sierra Marine | 18-6457 |
| Mallory | 9-29801 |
Engine & Model Compatibility
The company catalog identifies this pulley for the following engine families and marine-drive applications. The catalog does not establish one universal year range or every model and serial-number combination, so verify the exact engine and drive configuration before purchase.
| Engine Family | Configuration | Application | Notes |
|---|---|---|---|
| 4.3L | GM V6 | MerCruiser or Volvo Penta stern-drive/out-drive | For serpentine-belt systems using the listed pulley configuration |
| 5.0L | GM small-block V8 | MerCruiser or Volvo Penta stern-drive/out-drive | Verify pulley and belt dimensions before installation |
| 5.7L | GM small-block V8 | MerCruiser or Volvo Penta stern-drive/out-drive | Verify pulley and belt dimensions before installation |
| 8.1L | GM big-block V8 | MerCruiser or Volvo Penta stern-drive/out-drive | Verify engine configuration and original part reference |
Technical Specifications
- Product Type
- Serpentine belt idler pulley
- Construction
- Composite pulley
- Outside Diameter
- 3 inches
- Compatible Belt Width
- 13/16 inch
- Belt Type
- Serpentine
- Installation Location
- Engine belt-drive system
- Replacement Reference
- Mercury/MerCruiser 807757T
What’s in the Box
- 1 × Composite serpentine belt idler pulley
Mounting hardware, belt, tensioner, and other components are not included unless specifically shown or listed with the product.
Installation Notes
- Turn off the engine, allow it to cool, and disconnect the battery before service.
- Record or photograph the serpentine belt routing before removing the belt.
- Use the correct tool to release belt tension and remove the belt safely.
- Remove the existing idler pulley using the appropriate socket and tools.
- Inspect the mounting surface, belt, tensioner, and neighboring pulleys for wear or damage.
- Compare the replacement pulley with the original for diameter, belt width, mounting position, and alignment.
- Install the replacement pulley and tighten the fastener to the engine manufacturer's specified torque.
- Route the serpentine belt according to the original routing diagram and ensure every rib is correctly seated.
- Restore belt tension, rotate the system by hand where appropriate, and check pulley alignment.
- Reconnect the battery, start the engine, and inspect the pulley and belt for smooth, quiet operation.
Troubleshooting & FAQ
Which engines is this idler pulley listed for?
The company catalog lists 4.3L GM V6, 5.0L and 5.7L GM small-block V8, and 8.1L GM big-block V8 applications for MerCruiser and Volvo Penta stern-drive or out-drive systems. Always verify the exact engine and belt-drive arrangement.
What reference numbers can I use for comparison?
Listed references include Mercury/MerCruiser 807757T, Volvo Penta 3860201, Sierra Marine 18-6457, and Mallory 9-29801. Reference-number comparison should be combined with dimensional and application checks.
What belt does this pulley use?
It is intended for a serpentine belt approximately 13/16 inch wide. Confirm the belt width and pulley profile on your engine before ordering.
What are common signs of an idler pulley problem?
Squealing, rattling, rough rotation, pulley wobble, bearing noise, belt misalignment, or visible cracking can indicate that the pulley or another belt-drive component needs inspection.
Should the belt be replaced at the same time?
Inspect the belt whenever the idler pulley is serviced. Replace the belt if it is cracked, glazed, frayed, contaminated, incorrectly sized, or otherwise worn.
Is this an OEM part?
No. This is an aftermarket replacement pulley intended for the listed applications and reference numbers.
Do I need special tools for installation?
Installation normally requires standard mechanic's tools and a suitable serpentine-belt tension-release tool or long-handled ratchet, depending on the engine layout.
How can I confirm fitment?
Compare your original pulley with the listed references, 3-inch outside diameter, 13/16-inch belt width, mounting arrangement, and belt routing. Also verify the engine family and stern-drive or out-drive configuration before purchase.
Safety & Important Information
- Confirm the engine family, drive configuration, original reference number, pulley diameter, belt width, and alignment before ordering.
- Do not rely on engine displacement alone to establish fitment; variations may exist by model, drive, year, or serial number.
- Do not operate the engine with a damaged, misaligned, or incorrectly routed serpentine belt.
- Professional installation is recommended when the correct torque, belt routing, or service procedure is uncertain.
- This is an aftermarket replacement, not an OEM component.
About Sea Sierra
- Marine Replacement Parts — We provide aftermarket components for marine engine and drive-system service.
- Application-Focused Information — Product references and compatibility details are presented to help you compare the replacement with your original part.
- Fitment First — Always verify the engine, drive configuration, dimensions, and reference numbers before installation.
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