Idler Pulley – Fits Volvo Penta D4/D6 (Replaces 21280913, 3848896)
Idler Pulley – Fits Volvo Penta D4/D6 (Replaces 21280913, 3848896) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Idler Pulley – Fits Volvo Penta D4/D6 (Replaces 21280913, 3848896)
Product Details
This aftermarket Idler Pulley – Fits Volvo Penta D4/D6 Marine Diesel Engines (Replaces 21280913, 3848896) is designed for reliable compressor belt tensioning. It is compatible with specific Volvo Penta D4 series models (D4-260, D4-300) up to serial number 2004017297 and D6 series models (D6-350, D6-370, D6-400, D6-435) up to serial number 2006032252.
This component is a direct interchange for Volvo Penta part numbers 21280913, 3848896, 3809465, 3883786, and 21172053.
- Installs in the engine's compressor belt system.
- Engineered for marine diesel environments.
- Includes a 1-year aftermarket warranty.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Volvo Penta | 21280913 | Supersedes 3848896 |
| Volvo Penta | 3848896 | - |
| Volvo Penta | 3809465 | - |
| Volvo Penta | 3883786 | - |
| Volvo Penta | 21172053 | - |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Volvo Penta | D4-260 | 260 | 4-Stroke | 21280913 | Up to SN 2004017297 |
| Volvo Penta | D4-300 | 300 | 4-Stroke | 21280913 | Up to SN 2004017297 |
| Volvo Penta | D6-350 | 350 | 4-Stroke | 21280913 | Up to SN 2006032252 |
| Volvo Penta | D6-370 | 370 | 4-Stroke | 21280913 | Up to SN 2006032252 |
| Volvo Penta | D6-400 | 400 | 4-Stroke | 21280913 | Up to SN 2006032252 |
| Volvo Penta | D6-435 | 435 | 4-Stroke | 21280913 | Up to SN 2006032252 |
Technical Specs
- Product Type
- Idler Pulley / Tensioner Pulley
- Installation
- Engine Compressor Belt System
- Fuel Type
- Diesel
- Warranty
- 1 Year (Aftermarket)
- Other Technical Attributes
- For compressor belt tensioning in marine diesel engines
What’s in the Box
- 1 x Idler Pulley (21280913)
Installation Notes
A typical installation involves these steps:
- Disconnect the vessel's battery system before beginning work.
- Locate the compressor belt drive system and identify the idler pulley.
- Carefully release the tension from the belt and slide it off the pulley.
- Unbolt and remove the old idler pulley, noting its orientation.
- Clean the pulley mounting surface to ensure a secure fit.
- Mount the new idler pulley and tighten the fastening bolt to the engine manufacturer's recommended torque.
- Re-route the belt correctly around all pulleys according to the engine diagram.
- Apply tension back to the belt as specified by the manufacturer.
- Reconnect the battery, start the engine, and visually inspect the new pulley for smooth rotation and proper belt alignment.
Troubleshooting & FAQ
How do I confirm this fits my D4 or D6 engine?
Check your engine’s serial number. This idler pulley is specifically for D4 models up to serial number 2004017297 and D6 models up to serial number 2006032252. If your serial number is higher, you will require a different part.
What are the signs of a failing idler pulley?
Common symptoms include a persistent squealing or grinding noise from the engine, a noticeable wobble or free play in the pulley, or accelerated and uneven wear on the compressor belt.
When should the idler pulley be replaced?
The idler pulley should be inspected during routine belt service and replaced if it shows any signs of wear, damage, or bearing failure. It is often recommended to replace it at the same time as the belt and tensioner.
What is the difference between this and the OEM part?
This is an aftermarket replacement part, not an OEM component. It is designed to meet or exceed original equipment specifications for fit, form, and function, offering a reliable alternative at a competitive price.
Is this a tensioner or just an idler pulley?
This component is an idler pulley. It works within the compressor belt tensioning assembly to guide the belt and maintain proper alignment and tension as set by the tensioner.
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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