4.200 MLS Head Gasket .040 - SBM R3 Block

The 4.200 MLS Head Gasket .040 - SBM R3 Block by Cometic Gaskets is a precision-engineered cylinder head gasket designed for Small Block Mopar engines running R3 blocks. This gasket seals the critical interface between the cylinder head and engine block, preventing combustion gases and coolant from leaking into the oil galleries and vice versa. Whether you're rebuilding a classic Mopar, upgrading to higher compression, or maintaining consistent sealing on a modified engine, this multi-layer steel gasket delivers the reliable performance serious enthusiasts and professional builders expect.

Constructed from multi-layer steel (MLS) construction, this head gasket features a 4.200-inch bore diameter and 0.040-inch compression thickness, dimensions that match OEM specifications for R3 Small Block Mopar applications. MLS gaskets use multiple interlocking steel layers with elastomer coatings to provide superior sealing across a wider clamping range than traditional cork or composite gaskets. The 0.040-inch thickness is critical for maintaining proper combustion chamber volume and compression ratio—a specification that must be matched precisely during reassembly to avoid detonation or loss of power. Cometic's manufacturing tolerances ensure consistent performance across repeated heat cycles and varying engine loads.

This gasket is essential for anyone performing a head gasket replacement, engine rebuild, or head porting work on Small Block Mopar R3 block engines. It accommodates both stock and lightly modified applications, provided fastener torque specifications are followed correctly and the cylinder head and block deck surfaces are properly prepared and cleaned. Correct installation requires new head bolts (not reused fasteners), precise torque-to-yield procedures, and verification that your specific R3 block variant is compatible with the 4.200-inch bore specification. Professional engine builders and DIY enthusiasts who prioritize leak-free sealing and long-term reliability choose MLS gaskets from established brands like Cometic for maximum peace of mind.