Center Main Caps - AMC 390-401

The Center Main Caps for AMC 390-401 from Pro-Gram Engineering are essential internal engine components designed for serious enthusiasts rebuilding or restoring classic AMC muscle cars and performance engines. These caps sit at the heart of your engine block's main bearing journal, supporting the crankshaft under extreme loads and rotational stress. Whether you're doing a complete engine rebuild, upgrading from worn factory caps, or building a high-performance variant, quality main caps are non-negotiable for durability, oil pressure retention, and long-term reliability.

Pro-Gram Engineering's center main caps are precision-machined to OEM specifications, ensuring proper bearing bore alignment and consistent clamping force when torqued to spec. The 390 and 401 cubic-inch AMC engines demand robust main bearing support to handle both stock and modified power outputs—these caps maintain structural integrity under boost, high RPM, and elevated cylinder pressures. Proper fitment and finish are critical; any deviation in cap height or bearing surface can cause misalignment, increased bearing wear, oil starvation, or catastrophic engine failure. Pro-Gram's manufacturing tolerances meet or exceed factory standards, guaranteeing reliable performance across stock, street, and competition builds.

Mechanics and engine builders restoring 1969–1991 AMC 390 and 401 engines will appreciate the precise engineering and dependable fit of these center main caps. Installation requires careful alignment with factory bolt holes and proper torque sequence to avoid binding or warping the block. These caps are compatible exclusively with AMC 390-401 platforms and should be paired with matching main bearing inserts and fresh ARP or OEM bolts for optimal results. Whether you're preparing an engine for a show car, daily driver, or high-output build, Pro-Gram's center main caps deliver the precision and durability your rebuild demands.