What does 'undersize 0.50in' mean for these bearings?

This means the bearings are manufactured to be 0.050 inches smaller in diameter than standard size. This is necessary when the crankshaft journals have been machined down (ground undersize) to remove wear or damage during an engine rebuild.

What is the construction of these main bearings?

These bearings feature a bimetal construction, which uses an aluminum base. This design helps ensure good performance and durability for the main bearing application.

Do these bearings come with installation instructions?

While specific installation instructions are not included with the bearings themselves, it is highly recommended to consult a factory service manual for your specific AMC or Jeep vehicle. Proper installation, including correct torque specifications and oil clearances, is critical for engine longevity.

Specifications

Brand: King Engine Bearings
Part #: MB5518AM050
UPC: 611500380488

King Engine Bearings AMC / Jeep 390 & 401 (Undersize 0.50IN) Crankshaft Main Bearing Set

Name: King Engine Bearings AMC / Jeep 390 & 401 (Undersize 0.50IN) Crankshaft Main Bearing Set
Brand: King Engine Bearings
SKU: king-engine-bearings-king-engine-bearings-amc-jeep-390-401-undersize-0-50in-cran-t14-360430
Price: 65.77 USD
Availability: BackOrder

$65.77

On Backorder — Expected to ship by Sep 23, 2026

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

King Engine Bearings crankshaft main bearing set for AMC/Jeep 390 & 401 engines. Undersize 0.50in.

Key Features

Fits AMC and Jeep 390 and 401 cubic inch engines.
Main bearing set is 0.050 inches undersize, intended for use with a machined crankshaft.
Constructed with a bimetal design featuring an aluminum base.
Designed to restore proper crankshaft support and oil clearance in your engine.
Compatible with a wide range of AMC and Jeep vehicles from 1966 to 1991.

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About this part

Product Details

If you're rebuilding the bottom end of your AMC or Jeep 390 or 401 engine, a fresh set of main bearings is crucial. These main bearings from King Engine Bearings are designed to replace your worn-out originals, helping to restore proper crankshaft support and oil clearance. They are built with a bimetal construction, featuring an aluminum base for good performance.

This particular set is undersize by 0.050 inches, which is important if your crankshaft journals have been machined down during a rebuild. King Engine Bearings is a well-known name in engine components, and these bearings are a solid option for many AMC and Jeep vehicles from the 1960s through the early 1990s, including models like the Jeep CJ, Cherokee, and various American Motors cars.