King Performance SI Main Crankshaft Bearing Set – MX-5 MK3 / NC 1.8 & 2.0 • MB5442SI

King Performance SI Main Crankshaft Bearing Set – MB5442SI

Precision-manufactured King Engine Bearings main crankshaft bearing set for Mazda MX-5 MK3 / NC, MK3.5 / NC2 and MK3.75 / NC3 1.8L and 2.0L MZR petrol engines (2005–2015), including compatible L8 and LF engine applications. Available in standard and 0.25mm undersize options to suit standard or appropriately reground crankshaft journals.

King's SI Series uses silicon-aluminium bi-metal bearing construction, combining an aluminium-based bearing material with silicon to provide reliable crankshaft support and durability in standard and moderately loaded engine applications.

Main crankshaft bearings support the rotating crankshaft within the engine block, providing accurately manufactured bearing surfaces and maintaining the essential pressurised oil film between the crankshaft journals and bearing shells.

The MB5442SI set contains five upper and five lower bearing shells, providing a complete main bearing shell set for all five crankshaft main bearing positions in compatible Mazda MZR engines.

Four main bearing positions use the standard-width bearing arrangement, while the centre main bearing position uses a wider bearing pair to suit the engine's original crankshaft support configuration.

These bearings are particularly suitable for standard engine rebuilding, crankshaft repairs, replacement of worn main bearings and engine refurbishment where a high-quality silicon-aluminium replacement bearing is required.

Available bearing sizes:

• STD – MB5442SI: Standard-size main crankshaft bearings for crankshafts retaining their original standard-diameter main journals.
• 0.25mm – MB5442SI0.25: Undersize main bearings for crankshafts with main journals professionally reground 0.25mm below their original standard diameter.

Important – Correct Bearing Size: The 0.25mm option is intended for a crankshaft machined 0.25mm undersize. It is not an extra-clearance option for a standard crankshaft. Select the correct bearing size using accurate journal measurements, housing bore dimensions and the engine's specified installed oil clearances.

Product features and specifications:

• Product type: Main crankshaft bearing set
• Manufacturer: King Engine Bearings
• Product series: SI Series
• Bearing construction: Silicon-aluminium bi-metal
• Material: Lead-free aluminium-based bearing alloy
• Primary use: Crankshaft main journal support
• Location / system: Engine crankshaft / bottom-end assembly
• Engine family: Mazda MZR L8 / LF
• Engine capacities: 1.8L and 2.0L
• Vehicle applications: Mazda MX-5 MK3 / NC, NC2 and NC3
• Main bearing positions: 1, 2, 3, 4 and 5
• Quantity supplied: 5 pairs / 10 bearing shells
• Standard crankshaft main journal diameter: 51.979–51.999mm
• Standard housing bore diameter: 57.018–57.036mm
• Nominal STD shell wall thickness: 2.504mm
• Shell width, positions 1, 2, 4 and 5: 19.10mm
• Shell width, centre position 3: 25.85mm
• Available sizes: STD and 0.25mm undersize
• King product family: MB5442SI
• Manufacturer part number: Dependent on selected size option

SI Series Bearing Construction: King uses an aluminium-based bi-metal bearing material incorporating silicon, providing a lead-free bearing solution suited to original-equipment replacement and engine rebuilding. This SI design differs from King's XP Racing bearings, which use a high-performance tri-metal construction and pMaxBlack overlay technology.

Common replacement reasons: Main bearing replacement may be required following bearing wear, excessive main bearing oil clearance, oil starvation, crankshaft journal damage or during engine dismantling and rebuilding. The appropriate bearing size depends on the condition and dimensions of the crankshaft journals.

Fitment advice: Designed for Mazda MZR engines using the MB5442 main bearing configuration. STD bearings suit correctly measured standard-size crankshafts. The 0.25mm undersize version requires the corresponding crankshaft main journals to have been machined to the correct reduced diameter. Always verify bearing clearances during installation.

Other items to consider: When rebuilding an engine bottom end, you may also want to consider suitable connecting rod bearings, crankshaft oil seals, engine gasket sets, oil pump components, timing chain components, engine oil, oil filter, sump sealing materials and suitable engine assembly lubricant. For higher-load engine builds, the King Racing MB5442XP main bearing range offers a different performance-oriented bearing construction.

Useful tools / consumables: Precision micrometers, dial bore gauge, calibrated torque wrench, engine stand, suitable bearing clearance measuring equipment, engine assembly lubricant and appropriate workshop cleaning equipment.

Difficulty guide: DIY Difficulty: Advanced. Main bearing replacement requires substantial engine disassembly, crankshaft inspection, accurate dimensional measurement and correct bearing clearance selection. Professional engine-building experience and suitable precision measuring equipment are strongly recommended.

Why King Engine Bearings? King Engine Bearings specialises in precision-manufactured engine bearing components for original-equipment replacement, engine rebuilding and performance applications. Its SI Series uses silicon-aluminium bi-metal technology to provide accurate, durable and reliable crankshaft bearing solutions for compatible engines.

What's in the box: 1 × King Engine Bearings MB5442SI Main Crankshaft Bearing Set in the selected size, containing 5 upper and 5 lower main bearing shells (10 shells total).

Installation / service notes: Before installing the bearings, measure each crankshaft main journal and main bearing housing bore. Check for scoring, wear, taper and out-of-round journals. Select the correct bearing size and verify the installed oil clearance for each main bearing position. Clean the crankshaft oil passages, bearing housings and surrounding engine components thoroughly. Install each bearing shell in its correct position, paying particular attention to the wider centre main bearing pair. Lubricate the bearing surfaces during engine assembly and tighten the main bearing fasteners using the specified tightening sequence and torque procedure. Confirm that the crankshaft rotates freely and that crankshaft end float is within the required limits before completing the rebuild. Prime the lubrication system before initial engine startup.