4.340 MLS Head Gasket .040 - 426 Hemi

The 4.340 MLS Head Gasket .040 - 426 Hemi from Cometic Gaskets is a precision cylinder head gasket engineered for the legendary Mopar 426 Hemi engine platform. This component is essential for builders and enthusiasts restoring or upgrading classic high-performance Mopar muscle cars, as it forms the critical seal between the cylinder head and engine block. The gasket prevents combustion gases, coolant, and oil from leaking across the head surface while maintaining proper compression and thermal integrity under demanding engine conditions.

Cometic's multi-layer steel construction delivers superior durability and reliability compared to traditional composite gaskets, particularly in high-compression and turbocharged applications. The 4.340-inch bore diameter is precisely matched to 426 Hemi specifications, while the 0.040-inch compression thickness is critical for achieving correct deck height and combustion chamber volume—even 0.010 inch of variation can affect ignition timing and engine performance. The MLS (multi-layer steel) design uses independent layers that allow micro-movement and maintain sealing integrity across thermal cycles, preventing common head gasket failures caused by expansion and contraction in vintage and modified engines.

This gasket is ideal for engine builders, restoration shops, and serious enthusiasts performing top-end work on 426 Hemi engines, whether for original restorations or modern performance builds. Proper installation requires clean, flat machined surfaces and correct torque specifications to the head bolts—surface preparation is as critical as the gasket itself for long-term reliability. The 0.040-inch thickness specification must match your engine's machining specifications exactly; verify deck height and head-to-block measurements before installation to ensure optimal compression ratio and prevent future leaks.