What is the purpose of undersize bearings?

Undersize bearings, like this .025mm set, are used when a crankshaft has been ground down to remove imperfections or damage. The undersize bearing compensates for the material removed from the crankshaft, restoring the correct oil clearance for proper engine lubrication.

What is the tri-metal overlay on these bearings?

The tri-metal overlay is a combination of three different metal layers applied to the bearing surface. This construction is chosen for its excellent ability to withstand high loads and resist wear, which is crucial for performance engine applications.

Do I need to replace the main bearing bolts as well?

It is highly recommended to replace main bearing bolts when installing new bearings, especially in a performance engine build. Torque-to-yield bolts should always be replaced, and it's good practice to use new fasteners for critical engine components.

Specifications

Brand: ACL
Part #: 7M1397H-.025

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-t14-631205
Price: 311.90 USD
Availability: BackOrder

$311.90

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Key Features

Fits select BMW 1 Series M, 135i, 335i, 335is, 335xi, 335i xDrive, 535i, 535xi, 535i xDrive, 740i, 740Li, X6, and Z4 models.
RACE Series crankshaft main bearing set designed for high-performance BMW N54, N55, and S55B30 3.0L inline-6 engines.
Features a tri-metal overlay for improved load capacity and wear resistance.
Manufactured to precise tolerances for proper oil clearance.
This set is .025mm undersize, intended for use with a ground crankshaft.

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About this part

Product Details

Already running a built N54, N55, or S55B30 engine? This RACE Series crankshaft main bearing set from ACL is the next piece of the puzzle for serious performance. These bearings are built to handle the increased stress and higher RPMs that come with a performance engine build, ensuring your crankshaft stays properly supported under demanding conditions.

ACL uses a tri-metal overlay on these RACE Series bearings, which is a well-built combination of materials designed for excellent load-carrying capacity and wear resistance. They are manufactured to tight tolerances, with a .025mm undersize to account for crankshaft grinding during a rebuild. This precision means they'll fit right and provide the critical oil clearance needed for proper lubrication and engine longevity when you're pushing the limits.

This set is specifically for the 3.0L inline-6 engines found in a range of BMW models, including the 1 Series M, 135i, 335i, 535i, 740i, X6, and Z4. If you're rebuilding or upgrading your BMW's engine, these bearings are a solid option for ensuring reliable performance.