Main bearings STD BMW 1969-1993 2494-3210-3430cc ACL ACL Race bearings are designed to work in the most extreme conditions and the most demanding engines. Thanks to many years of experience in the production of bushings, each set is perfectly matched to the engine. The advanced technological process allows the bushing adapt to high RPM deformation and assist in the formation of hydrodynamic oil films. This technology, combined with the advanced geometry of the bushings, makes them ideal for heavily stressed engines. Most bushings are also available in several other dimensions: STDX -0.025 mm ( looser than nominal) STD +0.000 mm (nominal) +0.025 mm (tighter than nominal) +0.25 mm (first shaft grinding) +0.50 mm (second shaft grinding)