ACL 5M8353H-STD Race Main Bearing Set Standard Mazda B6 BP BPT 1.6 1.8 MX5 Miata

Vehicle Fitment

• 1990-2005 Mazda MX-5 Miata (NA/NB) - B6-ZE 1.6L DOHC 16v (1990-1993) and BP-ZE / BP-VE 1.8L DOHC 16v (1994-2005)
• 1986-1994 Mazda 323 - B6 / B6T 1.6L DOHC 16v (NA and Turbo)
• 1992-1995 Mazda MX-3 - B6 1.6L DOHC 16v
• 1990-2001 Mazda Protege - BP 1.8L DOHC 16v; ZL-VE, ZM-DE variants
• 1994-1997 Kia Sephia - B6 1.6L DOHC 16v
• 2001-2005 Kia Rio - B6 1.6L DOHC 16v
• 1991-1994 Mercury Capri - BP 1.6L / 1.8L DOHC
• Ford Laser (various markets) - BP-T 1.8L DOHC 16v Turbo

Fitment Notes

• This single set covers the complete Mazda B6 (1597cc) and BP (1839cc) DOHC 16v engine family - both naturally aspirated and turbocharged variants share the same crankshaft main journal dimensions, making one set applicable across all listed engines and displacements.
• Standard (STD) crankshaft main journal diameter - for use with stock or unworn journals at factory diameter only. For reground crankshafts, use 5M8353H-.25 (+0.25mm) or 5M8353H-.50 (+0.50mm) as appropriate.
• An HX extra-clearance variant (5M8353HX-STD) is also available for builders targeting approximately 0.025mm (0.001") additional running clearance at standard journal diameter without crankshaft grinding.
• Always measure crankshaft main journal diameter with a micrometer before selecting bearing size. Confirm actual clearance with Plastigage or a dial bore gauge after assembly.
• Sold as a complete set of 10 bearing shells (5 pairs, upper and lower) - sufficient for all 5 main journal positions in one 4-cylinder engine.

Features

• Tri-metal construction: copper-lead alloy lining bonded over a hardened steel backing, with a high-strength overlay plate - engineered for the high-RPM demands of naturally aspirated and turbocharged Mazda B6 and BP engines.
• Hardened steel backing on all main bearings improves structural support of the bearing lining and maintains crush under the elevated crank loads of boosted BP-T and B6T builds.
• High-strength overlay plate with reduced thickness provides improved fatigue resistance compared to OEM-spec bearings - an important upgrade for any Miata, 323 Turbo, or Protege performance rebuild.
• Increased bearing crush and tighter wall tolerances ensure consistent, secure seating in the block main journal bores, reducing the risk of bearing movement.
• Enlarged ID chamfers on bearing edges accommodate the larger fillet radii found on performance and aftermarket Mazda crankshafts.
• 3/4-groove upper main bearings optimize oil supply to the main journals and to the connecting rod bearings through the crankshaft oiling passages.
• Elimination of flash plating on bearing backs improves heat transfer and maximizes grip between the bearing shell and the block main bore.
• Increased eccentricity compensates for bore distortion at high RPM and assists in the formation of a stable hydrodynamic oil film under load.

Specifications

• Part Number: 5M8353H-STD
• Product Line: ACL Race Series
• Application: Crankshaft Main Bearings
• Engine Compatibility: Mazda B6 variants (1597cc DOHC 16v NA/Turbo); Mazda BP variants (1839cc DOHC 16v NA/Turbo) - including B6D, B6T, B6-ZE, BP, BP-VE, BP-ZE, BP-ZET, BPT, ZL-VE, ZM-DE
• Crankshaft Size: Standard (STD - Unground)
• Shaft (Main Journal) Diameter: 49.938-49.956mm (1.9661-1.9668 in)
• Tunnel (Housing Bore): 53.998-54.018mm (2.1259-2.1267 in)
• Maximum Wall Thickness at Crown: 2.013mm (0.0793 in)
• Maximum Overall Length: 17.63mm (0.694 in)
• Bearing Material: Tri-Metal Copper-Lead Alloy / Hardened Steel Backing
• Quantity: Set of 10 Shells - 5 Upper + 5 Lower (complete engine set)

Included Components

• 10x Race Series Crankshaft Main Bearing Shells - Standard Size (5 upper, 5 lower)

Product Description

The ACL Race Series 5M8353H-STD crankshaft main bearing set is the standard-size performance replacement for Mazda's B6 and BP DOHC 16v inline-4 engine family - spanning the beloved NA and NB Miata, the turbocharged 323, MX-3, Protege, and related Ford and Kia platforms that share the same B/BP-series architecture. The B6 (1.6L) and BP (1.8L) share identical crankshaft main journal dimensions, making a single bearing set applicable across all naturally aspirated and turbocharged variants from 1986 through the mid-2000s.

Used in championship-winning Miata race engines according to 949 Racing, these ACL Race Series main bearings deliver superior fatigue resistance, crush retention, and oil film stability over OEM Mazda shells. A reliable foundation for any B6 or BP rebuild - from a high-mileage Miata refresh to a turbocharged 323 or BP-T performance build. Always confirm clearances at assembly. Sold as a complete set of 10 shells for one engine.