Carrillo BMR4220-040 Pro-H Forged Connecting Rod BMW R-Series Boxer Twin

The Carrillo BMR4220-040 is a precision-forged, high-performance connecting rod engineered for BMW R-series boxer twin motorcycle engines with a 4.080" bore and 3.310" stroke. Built to the exacting standards that have made Carrillo the benchmark in race-engine connecting rods, this rod is designed for builders demanding maximum strength and reliability in performance street and competition applications.

Manufactured from Carrillo's proprietary "Carrilloy" alloy — a chrome, nickel, molybdenum, vanadium steel that meets all VAR (Vacuum Arc Re-Melt) ASTM standards — each rod is forged from an oversized billet to ensure optimal grain flow and the elimination of surface inclusions. Heat treatment is validated by both the supplier and an independent metallurgist to confirm the desired physical and chemical properties, resulting in a UTS of 195,000 PSI with a yield of 182,000 PSI.

Key Features:

• Rod Length: 6.123 in. (155.52 mm) center-to-center
• Bore Size: 4.080 in. (103.6 mm)
• Stroke: 3.310 in. (84.1 mm)
• Wrist Pin Diameter: 0.984 in. (25 mm)
• Wrist Pin Length: 2.500 in. (63.5 mm)
• Rod Weight: 346 grams (0.76 lbs) — optimized for strength-to-weight ratio
• Bolt Type: CARR (Multiphase) fasteners — rated for indefinite torque cycles when stretch method is followed
• Proprietary Carrilloy alloy steel — chrome, nickel, moly, vanadium construction
• VAR (Vacuum Arc Re-Melt) certified steel for maximum metallurgical integrity
• Each rod is magnafluxed at least twice during production and Rockwell hardness tested
• Final shot-peen operation for enhanced fatigue resistance
• All CNC machining features in-process probing for dimensional validation
• Made in the USA at Carrillo's Irvine, California facility

The BMR4220-040 is sold individually. For a full set, multiple units will be required. Carrillo's CARR Multiphase fasteners provide 285,000 UTS clamping force and are designed for indefinite reuse when installed using the proper stretch method with recommended lubricant. This rod is designed to work with performance aftermarket pistons and will not work with factory OEM pistons.