ACL Race Series connecting rod bearings for Mazda 3 and MX-5 NC (2.0L LF MZR Duratec)
Fits
Mazda
MX-5Mazda 3- Shipping in 24-48 hSubject to availability
- 14 days to returnUnfitted and in its original packaging
- Pay in instalmentsFinance your purchase at checkout
- Collection at our shopCartagena, Spain
These ACL Race Series connecting rod bearings, part number 4B4390H, are for the Mazda 3 and MX-5 NC (2.0L LF MZR Duratec). They are the standard choice when opening an engine for tuning.
They are tri-metal bearings: a SAE 1010 steel backing, a copper-lead-tin intermediate layer approximately 0.3 mm thick, a nickel barrier, and an overlay of lead, tin, and copper that conforms to the crankshaft surface and resists seizing. In the rod bearings, the overlay is thinner to better withstand fatigue.
Compared to a stock bearing, the Race series features increased crush, which improves seating and heat transfer, as well as greater eccentricity to support the oil film at high engine speeds.
In the standard size, ACL specifies them for a rod journal of 46.980 to 47.000 mm, with a bearing width of 16.25 mm. For that diameter, they recommend an oil clearance of approximately 0.051 to 0.060 mm, measured with a micrometer and bore gauge. If the crankshaft has been reground, the measurements will change.
They do not have the silver-tin flash plating of standard bearings, so their dark color—ranging from brown to black and blue—is how they come from the factory and does not indicate any defect. ACL advises against polishing the bearing surface to adjust clearance; if more is needed, they should be combined with the HX version, which provides an additional 0.025 mm of clearance.
Not sure if your crankshaft is at standard size? Send us your engine code and we will help you choose.