Main Bearing Kit – Fits Volvo Penta AQD21A/B, MD21A/B Diesel Engines (Replaces 875306)
Main Bearing Kit – Fits Volvo Penta AQD21A/B, MD21A/B Diesel Engines (Replaces 875306) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Main Bearing Kit – Fits Volvo Penta AQD21A/B, MD21A/B Diesel Engine...
Product Details
This standard-sized Main Bearing Kit contains the bearing halves that support the crankshaft in the engine block for Volvo Penta AQD21A, AQD21B, MD21A, and MD21B diesel engines. This kit is not to be confused with connecting rod or big end bearings, as it is designed specifically for crankshaft placement.
This kit serves as a direct replacement for Volvo Penta 875306 and Orbitrade 11306, offering a reliable aftermarket alternative.
- Fits standard size crankshafts (not for oversized applications).
- Installs directly into the engine block to support the crankshaft.
- Constructed from durable steel with a high-performance bearing alloy surface.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.
| Brand | Part Number |
|---|---|
| Volvo Penta | 875306 |
| Orbitrade | 11306 |
Engine & Model Compatibility
Confirm your engine model in the table below. This kit is designed for specific Volvo Penta diesel engines.
| Brand | Model | Stroke | OEM Part No. |
|---|---|---|---|
| Volvo Penta | AQD21A | Diesel | 875306 |
| Volvo Penta | AQD21B | Diesel | 875306 |
| Volvo Penta | MD21A | Diesel | 875306 |
| Volvo Penta | MD21B | Diesel | 875306 |
Technical Specs
- Product Type
- Crankshaft Main Bearing Kit
- Installation Location
- Engine Block
- Material
- Steel with Bearing Alloy Surface
- Dimensions (L x W x H)
- 16.0 cm x 7.0 cm x 3.0 cm
- Weight
- 0.31 kg (0.68 lb)
- Fitment
- Standard Size (not oversized)
- Engine Applications
- AQD21A, AQD21B, MD21A, MD21B
- Important Notes
- Does not include the thrust washer (sold separately; see Orbitrade 11262).
What’s in the Box
- Crankshaft Main Bearing Halves (Replaces 875306)
Installation Notes
- Thoroughly clean the engine block and crankshaft, ensuring all oil galleries are clear of debris.
- Verify bearing sizes and crankshaft journal dimensions against your service manual's specifications.
- Install the upper grooved bearing halves into the engine block, ensuring the locking tabs are correctly seated.
- Carefully lower the crankshaft into place onto the installed upper bearings.
- Place the lower bearing halves into the main bearing caps.
- Apply a generous amount of assembly lube to all bearing surfaces and crankshaft journals.
- Install the main bearing caps and tighten the bolts in sequence to the manufacturer's recommended torque specifications.
- After torquing, confirm that the crankshaft rotates freely without binding.
Troubleshooting & FAQ
What is the difference between main bearings and connecting rod bearings?
Main bearings support the crankshaft within the engine block, allowing it to rotate smoothly. Connecting rod bearings are located at the "big end" of the connecting rods where they attach to the crankshaft. This kit is only for the crankshaft main bearings.
Is this a standard size or oversized bearing kit?
This is a standard-sized kit. It is not suitable for crankshafts that have been machined down and require oversized bearings. Always measure clearances and consult your service manual before ordering.
What are the signs of failing main bearings?
Symptoms of worn main bearings include a deep, hollow knocking sound from the engine, persistently low oil pressure, and the presence of metallic flakes (bearing material) in the engine oil and filter.
Does this kit include the thrust washer?
No, the thrust washer is not included in this kit and must be purchased separately if replacement is needed. A common aftermarket cross-reference for the corresponding thrust washer is Orbitrade 11262.
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
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