King Racing XP Main Crankshaft Bearing Set – MX-5 MK1 / MK2 / MK2.5 1.6 & 1.8 • MB5304XP

King Racing XP Series Main Crankshaft Bearing Set – MB5304XP

Performance main crankshaft bearing set for Mazda MX-5 MK1 / NA, MK2 / NB and MK2.5 / NB-FL 1.6L B6 and 1.8L BP petrol engines (1989–2005), including compatible 1.8 VVT engine applications. Available in four bearing size options to suit standard and appropriately machined crankshafts.

The King Racing XP Series is developed for performance engine building and demanding motorsport use. Manufactured using King's high-performance tri-metal bearing construction and pMaxBlack overlay technology, these bearings are designed to provide excellent load-carrying capacity, controlled oil-film performance and durability in engines operating under increased mechanical loads.

Main crankshaft bearings support the crankshaft within the engine block, allowing it to rotate on a pressurised film of engine oil while maintaining the correct operating clearance between the crankshaft journals and bearing surfaces.

The MB5304XP set contains five pairs of main bearing shells, providing the upper and lower bearings for all five crankshaft main bearing positions in compatible Mazda B6 and BP engines.

Suitable for performance engine rebuilds, bottom-end overhauls, competition engine preparation and replacement of worn or damaged main bearings, the range offers a choice of standard, extra-clearance and undersize-journal options.

Available bearing sizes:

• STD – MB5304XP: Standard-size main bearings for crankshafts retaining standard journal dimensions.
• STDX – MB5304XPSTDX: Standard-journal bearings with approximately 0.025mm (0.001 inch) additional oil clearance compared with the standard version, for appropriately specified performance engine builds.
• 0.25mm – MB5304XP0.25: Main bearing shells designed for crankshaft journals ground 0.25mm below standard diameter.
• 0.50mm – MB5304XP0.5: Main bearing shells designed for crankshaft journals ground 0.50mm below standard diameter.

Product features and specifications:

• Product type: Performance main crankshaft bearing set
• Product series: King Racing XP
• Bearing construction: High-performance tri-metal copper-lead
• Overlay technology: King pMaxBlack
• Primary use: Crankshaft main journal support
• Location / system: Engine bottom end / crankshaft assembly
• Engine applications: Mazda B6 1.6L and BP 1.8L
• Vehicle applications: Mazda MX-5 MK1 / NA, MK2 / NB and MK2.5 / NB-FL
• Main bearing positions: 1, 2, 3, 4 and 5
• Quantity supplied: 5 pairs / 10 bearing shells
• Standard crankshaft journal diameter: 49.939–49.957mm
• Standard bearing housing diameter: 53.998–54.018mm
• Nominal bearing shell width: 17.5mm
• Available sizes: STD, STDX, 0.25mm and 0.50mm
• Thrust washers: Not included; sold separately
• Compatible King thrust washer set: TW133AM
• Brand: King Racing / King Engine Bearings
• Product family: MB5304XP
• Manufacturer Part No.: Dependent on selected size option

Common replacement reasons: Main bearing replacement may be required following bearing wear, engine oil starvation, excessive bearing clearance, crankshaft journal damage or a major engine rebuild. Performance engine builds may also require a specific bearing clearance to suit the intended operating conditions and engine builder's specifications.

Fitment advice: Designed for compatible Mazda B6 and BP engines using the specified five-main-bearing crankshaft arrangement. Selecting the correct bearing size is essential. STD is intended for standard crankshaft journals, while STDX provides additional oil clearance. The 0.25mm and 0.50mm options are intended for crankshafts with the corresponding journal undersize. Bearing selection must be based on accurate crankshaft and housing measurements rather than engine model alone.

Important: This main bearing set does not include crankshaft thrust washers. King Racing TW133AM thrust washers are available separately from MazSpec.

Other items to consider: When rebuilding the engine bottom end, you may also want to consider King Racing TW133AM thrust washers, King Racing CR4002XP connecting rod bearings, replacement crankshaft seals, oil pump components, engine gasket sets, sump sealant, appropriate engine oil, oil filter and engine assembly lubricant.

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

Difficulty guide: DIY Difficulty: Advanced. Main bearing replacement requires substantial engine dismantling and accurate measurement of the crankshaft journals, bearing housing bores, bearing oil clearances and crankshaft end float. Professional engine-building knowledge and suitable precision measurement equipment are strongly recommended.

Why King Racing? King Engine Bearings specialises in precision engine bearing manufacturing for standard, performance and motorsport applications. Its XP Racing Series combines advanced bearing material technology with the pMaxBlack overlay, engineered to withstand the demanding operating conditions associated with high-performance engines. The range provides engine builders with options for standard, extra-clearance and reground crankshaft applications.

What's in the box: 1 × King Racing MB5304XP Series Main Bearing Set in the selected size, containing 5 upper and 5 lower main bearing shells (10 shells total). Crankshaft thrust washers are not included.

Installation / service notes: Before installation, accurately measure all crankshaft main journals and main bearing housing bores to establish the required bearing size and operating clearance. Inspect the crankshaft for scoring, taper, out-of-round wear and other damage. Ensure all oil passages and bearing surfaces are completely clean. Install bearings in the correct upper and lower positions, lubricate according to engine assembly procedures and tighten main bearing caps using the correct sequence and torque specifications. Verify oil clearance and crankshaft rotation during assembly, and measure crankshaft end float using the correctly specified thrust washers. Prime the engine lubrication system before initial startup. Incorrect bearing size or installation can result in severe engine damage.