King Racing XP Race Spec Main Crankshaft Bearing Set – MB5442XP
High-performance King Racing 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 Mazda L8 and LF engine applications. Available in five bearing sizes for precision engine rebuilding and performance engine preparation.
The King Racing XP Series is engineered for high-performance and motorsport engine applications, combining precision-manufactured copper-based tri-metal bearing shells with King's proprietary pMaxBlack hardened overlay technology.
Main crankshaft bearings support the crankshaft within the engine block, maintaining the oil film necessary for smooth rotation while transmitting substantial combustion and rotating assembly loads into the engine structure.
The MB5442XP set provides five matched pairs of main bearing shells for all five crankshaft main bearing positions. Four positions use standard-width bearing shells, while the centre main bearing position uses a wider bearing arrangement.
These race-spec bearings are designed for engine builders looking for precision bearing geometry, improved load capacity and appropriate oil clearance control during engine rebuilding, bottom-end repairs and high-performance engine preparation.
Available bearing sizes:
- STD – MB5442XP: Standard-size bearings for crankshafts retaining their standard journal dimensions.
- 0.25mm – MB5442XP0.25: Bearings for crankshaft main journals ground 0.25mm undersize.
- 0.026mm – MB5442XP.026: Precision sizing option designed to produce approximately 0.025mm (0.001 inch) LESS oil clearance than STD when installed on standard-size journals.
- 0.50mm – MB5442XP0.5: Bearings for crankshaft main journals ground 0.50mm undersize.
- STDX – MB5442XPSTDX: Extra-clearance bearings designed to produce approximately 0.025mm (0.001 inch) MORE oil clearance than STD when installed on standard-size journals.
Important – Selecting the Correct Size: The 0.026mm and STDX options provide different operating clearances and are not interchangeable. The 0.25mm and 0.50mm options require crankshafts machined to the corresponding undersize. Bearing selection must be based on accurate crankshaft journal, main bearing housing and installed clearance measurements.
Product features and specifications:
- Product type: Performance main crankshaft bearing set
- Series: King Racing XP
- Bearing material: Copper-based tri-metal
- Overlay technology: pMaxBlack
- Applications: Mazda MZR L8 / LF and compatible L3 / Ford Duratec engine configurations
- MX-5 application: MK3 / NC 1.8L and 2.0L petrol engines
- Crankshaft main bearing positions: 1, 2, 3, 4 and 5
- Quantity supplied: 5 pairs / 10 main bearing shells
- Standard crankshaft main journal diameter: 51.979–51.999mm
- Standard main bearing housing diameter: 57.018–57.036mm
- Nominal STD bearing wall thickness: 2.504mm
- Nominal shell width, positions 1, 2, 4 and 5: 19.10mm
- Nominal shell width, centre position 3: 25.85mm
- Available bearing sizes: STD, 0.25mm, 0.026mm, 0.50mm and STDX
- Brand: King Engine Bearings / King Racing
- Manufacturer part number: Dependent on selected variant
King Racing XP Bearing Technology:
- pMaxBlack: Proprietary hardened overlay designed for increased bearing load capacity.
- U-Groove: Oil-groove design intended to maintain oil delivery while optimising the available load-bearing surface.
- RadiaLock: Optimised bearing crush geometry to promote secure shell retention and heat transfer.
- EccentriX: Engineered bearing eccentricity to support hydrodynamic lubrication.
- Bull's Eye Tolerance: Precision wall-thickness manufacturing controls for consistent bearing clearances.
Common replacement reasons: Crankshaft main bearings may require replacement following excessive wear, oil starvation, bearing damage, crankshaft journal machining or during a complete engine rebuild. Performance engine builds can also require carefully selected bearing clearances appropriate to the engine's intended use.
Fitment advice: Designed for compatible Mazda MZR L8 and LF crankshaft main bearing arrangements. All five variants share the engine application, but the correct size depends on crankshaft machining, journal dimensions, main bearing housing dimensions and the engine builder's required operating clearances. Always measure components before selecting a bearing size.
Other items to consider: When replacing crankshaft main bearings, you may also want to consider suitable connecting rod bearings, crankshaft thrust components where required by the engine configuration, crankshaft front and rear oil seals, oil pump components, engine gasket sets, sump sealant, replacement engine fasteners, engine oil and assembly lubricant.
Useful tools / consumables: Precision micrometers, dial bore gauge, dial indicator, calibrated torque wrench, engine stand, suitable bearing clearance measuring equipment, engine assembly lubricant and appropriate engine cleaning materials.
Difficulty guide: DIY Difficulty: Advanced. Installation requires engine dismantling, crankshaft inspection, accurate bearing size selection and careful measurement of all installed bearing clearances. Professional engine-building experience and precision measuring equipment are recommended.
Why King Racing? King Engine Bearings specialises in precision bearing manufacturing for road, high-performance and motorsport engines. Its XP Racing Series combines high-performance tri-metal bearing materials with advanced overlay, lubrication and manufacturing technologies, providing a race-spec bearing solution for demanding Mazda MZR engine builds.
What's in the box: 1 × King Racing XP MB5442 Series Main Crankshaft Bearing Set in the selected size, containing 5 upper and 5 lower main bearing shells (10 shells total) for the five crankshaft main bearing positions.
Installation / service notes: Before installation, measure every crankshaft main journal and the corresponding engine block bearing housing bore. Check for scoring, taper, out-of-round wear and other crankshaft damage. Select the correct bearing size and verify all installed oil clearances against the engine builder's specification. Clean all bearing surfaces and lubrication passages thoroughly. Install each bearing shell in its correct location, observing the wider centre main bearing arrangement. Lubricate the bearings during assembly, tighten main bearing fasteners using the specified sequence and torque procedure, and confirm free crankshaft rotation and correct end float before completing the engine rebuild. Prime the lubrication system before initial startup.
| Make | Model | Sub Variant | Chassis / Code | Years | Power (PS) | Engine Codes | Fuel | Transmission | Notes |
|---|---|---|---|---|---|---|---|---|---|
| Mazda | MX-5 MK3 / NC | NC1 1.8L | NC18 | 2005–2008 | 126 | L8 | Petrol | 5-speed manual | Five-pair main bearing set; select correct size |
| Mazda | MX-5 MK3 / NC | NC1 2.0L | NC18 | 2005–2008 | 160 | LF | Petrol | 5/6-speed manual; automatic where fitted | Five-pair main bearing set; select correct size |
| Mazda | MX-5 MK3.5 / NC | NC2 1.8L | NC18 | 2009–2012 | 126 | L8 | Petrol | 5-speed manual | Five-pair main bearing set; select correct size |
| Mazda | MX-5 MK3.5 / NC | NC2 2.0L | NC18 | 2009–2012 | 160 | LF | Petrol | 5/6-speed manual; automatic where fitted | Five-pair main bearing set; select correct size |
| Mazda | MX-5 MK3.75 / NC | NC3 1.8L | NC18 | 2013–2015 | 126 | L8 | Petrol | 5-speed manual | Five-pair main bearing set; select correct size |
| Mazda | MX-5 MK3.75 / NC | NC3 2.0L | 2013–2015 | 160 | LF | Petrol | 5/6-speed manual; automatic where fitted | Five-pair main bearing set; select correct size |
| Reference Type | Reference |
|---|---|
| King Racing XP Main Bearings – STD | MB5442XP |
| King Racing XP Main Bearings – 0.25mm | MB5442XP0.25 |
| King Racing XP Main Bearings – 0.026mm | MB5442XP.026 |
| King Racing XP Main Bearings – 0.50mm | MB5442XP0.5 |
| King Racing XP Main Bearings – STDX | MB5442XPSTDX |
| King OE-Replacement Bearing Family | MB5442SI |