What is the difference between standard size and undersize bearings?

Standard size bearings are meant to be used with a crankshaft that is at its original factory dimensions or has been machined back to standard size. Undersize bearings are used when the crankshaft has been ground down (undersized) to remove damage or wear.

What material are these ACL main bearings made from?

These ACL Race Series main bearings are constructed from a tri-metal material. This composition is chosen for its balance of strength, wear resistance, and ability to maintain an oil film under demanding conditions.

Do I need to replace my crankshaft when installing these bearings?

You only need to replace or machine your crankshaft if it shows signs of significant wear or damage that exceeds the tolerance for standard size bearings. If the journals are within factory specifications or have been machined back to standard, these bearings will fit.

ACL BMW N63B44/S63B44 4.4L V8 Standard Size Main Bearings

Specifications

Brand: ACL
Part #: 5M1573H-STD
UPC: 9315726470220

ACL BMW N63B44/S63B44 4.4L V8 Standard Size Main Bearings

Name: ACL BMW N63B44/S63B44 4.4L V8 Standard Size Main Bearings
Brand: ACL
Price: 266.87 USD
Availability: InStock

$266.87

On Backorder — Expected to ship by Apr 10, 2026

Order now to reserve yours — we'll ship as soon as stock arrives. Full refund if we're unable to fulfill.

Fits 2012-2018 BMW M6. ACL standard size main bearings for N63B44/S63B44 4.4L V8 engines. Essential for engine rebuilds.

Key Features

Fits 2012-2018 BMW M6, 2013-2016 BMW M5, 2009-2012 BMW 750i, and 2011-2013, 2015-2018 BMW X5.
Standard size main bearing set for BMW N63B44 and S63B44 4.4L V8 engines.
ACL Race Series bearings feature a tri-metal material for improved strength and wear resistance.
Designed to provide proper crankshaft support and maintain correct oil clearance.
Well-built replacement for worn or damaged main bearings during engine rebuilds.

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Product Details

Already running a built engine or planning a rebuild on your 2012-2018 BMW M6? These standard size main bearings from ACL are a critical component for ensuring proper crankshaft support and oil clearance. They are designed for the N63B44 and S63B44 4.4L V8 engines, providing a well-built replacement for worn-out bearings.

ACL's Race Series bearings are known for their robust construction. They utilize a tri-metal material that offers excellent strength and wear resistance, crucial for maintaining consistent oil film between the crankshaft and the block. This set is standard size, meaning it's intended to be used with an un-machined or freshly machined crankshaft to factory specifications. Proper installation is key; ensure your crankshaft journals are within factory tolerances and that you follow the manufacturer's recommended torque and oil clearance specifications.

When rebuilding or refreshing your BMW's V8, using reliable components like these ACL main bearings is essential for long-term engine health. They are a solid option for anyone looking to restore their engine to proper operating condition.