What does it mean that these bearings are undersized by 0.25mm?

This means the inner diameter of the bearings is slightly smaller than standard. This is typically used when a crankshaft has been machined undersize to restore proper bearing clearance. You must ensure your crankshaft journals are also machined to match this 0.25mm undersize.

What is the advantage of the tri-metal overlay construction?

The tri-metal overlay provides a strong and durable bearing surface. It's designed to withstand higher loads and temperatures often found in performance or racing engines, offering better protection for your crankshaft.

Do these bearings come with new main bearing bolts?

This set includes the crankshaft main bearings only. New main bearing bolts are typically recommended for performance engine builds, and they are sold separately.

Specifications

Brand: ACL
Part #: 7M1397H-.25

ACL BMW N54/N55/S55B30 3.0L Inline 6 RACE Series Engine Crankshaft Main Bearing Set

Name: ACL BMW N54/N55/S55B30 3.0L Inline 6 RACE Series Engine Crankshaft Main Bearing Set
Brand: ACL
SKU: acl-acl-bmw-n54-n55-s55b30-3-0l-inline-6-race-series-engine-crankshaft-main-bear-t14-630762
Price: 311.90 USD
Availability: BackOrder

$311.90

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ACL RACE Series crankshaft main bearing set for BMW N54/N55/S55B30 3.0L engines. Undersize .25mm.

Key Features

Fits 13+ BMW models with N54, N55, and S55B30 3.0L inline-6 engines.
RACE Series bearings are built for high-performance applications.
Features a tri-metal overlay for improved strength and durability.
Main bearing set is undersized by 0.25mm.
ACL is a well-known manufacturer of engine bearings.

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About this part

Product Details

Doing a performance rebuild on your BMW with an N54, N55, or S55B30 3.0L inline-6 engine? These ACL RACE Series crankshaft main bearings are a solid choice for handling the increased demands of a performance build. They're designed to handle higher loads and temperatures than stock bearings, which is crucial when you're pushing your engine harder.

ACL has been making bearings for a long time, and their RACE Series is built with a special tri-metal overlay. This construction offers improved strength and durability, especially important for the main bearings that support the crankshaft. This particular set is undersized by 0.25mm, which is important to note if you're re-using your crankshaft. You'll want to ensure your crankshaft journals are also machined to the correct undersize for a proper fit and oil clearance.

If you're building a performance engine, getting the bearing clearances right is key to longevity and power. These ACL bearings are a well-built component that can help you achieve that goal. Make sure to check your engine's specific service manual for the correct oil clearance specifications when using undersized bearings.