ACL Race Series Rod Bearing Set (0.50mm Undersize) - NA/NB Miata (90-05)

ACL Race Series connecting rod bearing set in 0.50 mm undersize for the Mazda B6 1.6L and BP 1.8L engines in the 1990-1997 Mazda Miata (NA) and 1999-2005 Mazda Miata (NB). The 0.50 size is for a crankshaft whose rod journals have been reground 0.50 mm (.020 in.) undersize; the thicker shells take up the material removed. An original, unground crank takes the STD set (ACL 4B8351H-STD). One set covers all four connecting rods.

• ACL Race Series tri-metal construction: high-tensile SAE 1010 steel back, copper-lead-tin lining, nickel barrier and lead-tin-copper overlay (thinner overlay on rod bearings for fatigue resistance); no flash plating, so the shells look dark rather than silver
• Size 0.50 mm undersize: for rod journals reground 0.50 mm (.020 in.) below standard; not an oversize part
• For the 45 mm rod journal: ACL lists a standard crankpin diameter of 44.940-44.956 mm, a rod housing bore of 47.996-48.016 mm and a shell length of 17.00 mm; maximum STD wall 1.515 mm (1.502 mm for the HX extra-clearance set)
• Set for one engine: an upper and a lower shell for each of the four connecting rods (8 shells)
• ACL Race Series features: increased crush for bearing retention and heat transfer, increased eccentricity to allow for housing distortion at high rpm, and enlarged ID chamfers to clear larger crankshaft fillet radii
• ACL sizes for this application: HX-STD (standard crank, .001 in./0.025 mm extra oil clearance), STD, .025 (standard crank, about .001 in./0.025 mm less clearance), 0.25 mm and 0.50 mm undersize (reground crank). ACL notes grades can be mixed per journal: one HX-STD with one H-STD shell adds .0005 in. (0.013 mm); one H-STD with one H-.025 shell removes .0005 in. Measure journals and assembled bearing ID and choose the size that gives your target clearance

Fitment: Connecting rod (big-end) bearings for the Mazda B6 1.6L and BP 1.8L engines, which share rod journal sizes. 1990-1993 Mazda Miata (NA, 1.6L), 1994-1997 Mazda Miata (NA, 1.8L) and 1999-2005 Mazda Miata (NB), including the 2004-2005 Mazdaspeed. Not for the 2006+ MX-5 (NC/ND), which use different engines.

Part number: ACL 4B8351H-.50

This Part Fits: