MAHLE 40620.040 Plasma-Moly Engine Piston Ring Set 3.875 in. Bore +.040 Over 8-Cylinder

The MAHLE 40620.040 is a premium plasma-moly piston ring set engineered for 8-cylinder engines with a 3.875-inch bore at +0.040" oversize. Designed to OE form, fit, and function, this set delivers the precision and durability that professional engine builders demand for stock rebuilds and performance applications alike.

MAHLE is one of the world's largest OE piston ring manufacturers, and the 40620.040 reflects that expertise. The rings are pre-lapped for immediate seating, virtually eliminating traditional break-in time. Ring materials, coatings, and tension levels are all optimized for reduced friction, minimized oil consumption, and extended service life.

Key Features:

• Plasma-moly top ring coating for superior wear resistance and reduced friction
• Pre-lapped construction — seats immediately, virtually no break-in required
• SAE 9254 high alloy steel base material — higher tensile/yield strength, extended fatigue resistance, and increased hardness
• Barrel-faced compression ring contact area with CNC-controlled gap chamfer for optimized compression and reduced blow-by
• Reverse twist intermediate rings for superior groove-side sealing and enhanced contact via taper-race machining
• CP-20 oil ring assemblies with exclusive 20-degree ear angle for maximum side seal against the cylinder wall, plus chemically polished expander for enhanced oil drain-back
• Ring thicknesses: 5/64 in. (top), 3/32 in. (intermediate), 3/16 in. (oil)
• Fits 3.875 in. bore at +0.040" oversize
• Designed for 8-cylinder applications — sold as a complete set

MAHLE piston rings are driven by OE requirements, focusing on reducing ring mass and friction while delivering longer service life. Whether performing a routine engine overhaul or a high-performance rebuild, the 40620.040 provides the quality and reliability that engine professionals trust.