What does it mean for these bearings to be 0.025mm undersize?

This means the inner diameter of the bearing is slightly smaller than a standard size. This is intended for use with a crankshaft that has been machined down by 0.025mm. It ensures the correct oil clearance is achieved once installed.

Are these bearings suitable for a stock engine rebuild?

These are ACL Race Series bearings, which are built for performance applications. They are suitable for rebuilds where the crankshaft has been measured and machined to the specified 0.025mm undersize, whether for performance or to correct wear.

What else might I need when installing these main bearings?

When replacing main bearings, it's essential to have the crankshaft measured and machined if necessary. You'll also need a quality torque wrench to follow the manufacturer's torque specifications precisely, along with appropriate assembly lubricant.

ACL BMW N63B44/S63B44 4.4L V8 .025mm Oversized Main Bearings

Specifications

Brand: ACL
Part #: 5M1573H-.025
UPC: 9315726470190

ACL BMW N63B44/S63B44 4.4L V8 .025mm Oversized Main Bearings

Name: ACL BMW N63B44/S63B44 4.4L V8 .025mm Oversized Main Bearings
Brand: ACL
SKU: acl-acl-bmw-n63b44-s63b44-4-4l-v8-025mm-oversized-main-bearings-t14-719899
Price: 298.89 USD
Availability: BackOrder

$298.89

On Backorder — Expected to ship by Apr 23, 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 4.4L V8 main bearings, 0.025mm undersize, for reliable engine performance.

Key Features

Fits 2012-2018 BMW M6, 2013-2016 BMW M5, 2009-2012 BMW 750i, and 2011-2013, 2015-2018 BMW X5.
ACL Race Series main bearing set for BMW 4.4L V8 N63B44 and S63B44 engines.
Bearings are precision-machined to be 0.025mm undersize for crankshafts machined to this tolerance.
Well-built construction designed to handle the demands of performance V8 engines.
Helps achieve proper oil clearance for engine longevity and performance.

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Will this fit your vehicle?

Product Details

When your BMW's V8 engine needs new main bearings, especially after a rebuild or if you're pushing the limits, ACL Race Series bearings are a solid choice. These are designed for the N63B44 and S63B44 4.4L V8 engines found in a range of BMW models, including the 750i, M5, M6, and X5. They are precision-made to be 0.025mm undersize, which is crucial for ensuring proper oil clearance when working with crankshafts that have been machined to a specific tolerance.

ACL has been in the bearing game for a long time, and their Race Series bearings are built with performance and durability in mind. They use well-built materials and advanced manufacturing techniques to create bearings that can handle the stresses of a high-performance V8. Getting the oil clearance just right is key to engine longevity and performance, and these bearings help you achieve that critical specification when rebuilding or refreshing your engine.

If you're working on your engine, remember that main bearings are a critical component. Make sure your crankshaft has been properly measured and machined to the correct undersize before installing these bearings. It's also a good idea to have a quality torque wrench and follow the manufacturer's torque specifications precisely during installation to ensure everything seats correctly and performs as it should.