Reinforced ARP bolts for OEM rods BMW M20B25 M50B20 M50B25

The compatible BMW engines

The BMW M50 (2.0 and 2.5 litres) and the earlier M20B25 (2.5 litres) are the petrol inline-sixes fitted to the 3 Series (E36), 5 Series (E34), E30 and the Z1 roadster.

The original rod bolt of the M50 and M20B25 is a steel bolt with an M9 thread and a 53 mm under-head length (reference 11 24 1 713 342), tightened by torque then angle: this method takes it to its yield point and makes it single-use, BMW requiring replacement whenever the rods are dismantled.

Reinforced ARP bolts

The rod bolt is one of the most heavily loaded parts of the bottom end: on every cycle it takes the inertial loads of the whole rod-and-piston assembly. As standard, it is designed for series power only.

As soon as a build raises cylinder pressure and engine speed, this bolt reaches its limit. This kit replaces it with ARP2000 bolts, machined and inspected for higher fatigue strength and preload, without touching the rest of the rotating assembly.

Technical specifications

Tightening torque and stretch

In addition to torque tightening, ARP recommends checking by stretch measurement, which ensures an accurate preload. These torque and stretch values apply to tightening carried out with the ARP lubricant.

Technical guide

The ARP brand

Coming from the aerospace industry, Gary Holzapfel founded ARP (Automotive Racing Products) in the early 1970s to tackle a scourge of motorsport: engine failure caused by insufficiently strong fasteners. Today ARP designs and manufactures in the USA (California) thousands of references (head bolts, main bolts, rod bolts) in several material grades depending on the application, recognised for their manufacturing consistency and fatigue resistance. Each kit ships with its assembly lubricant and instructions detailing the steps, torque and tightening procedure.

Measuring bolt stretch

In addition to torque tightening, measuring stretch is the most reliable check for optimal preload. It is done with the bolt fitted: a gauge (dial indicator) is placed on both ends of the bolt and the actual stretch is read, which must match the recommended value (see the torque and stretch table above). This method eliminates the friction scatter of torque tightening and secures the assembly on heavily loaded engines.

Vehicle compatibility

OEM reference (rod bolt): 11 24 1 713 342 (M9 x 53 mm)

Why it is the most cost-effective solution?

If an original rod bolt gives way, the connecting rod breaks free and destroys the crankshaft and the block. Fitting ARP bolts removes this risk: it is one of the most cost-effective safeguards of any build.

Why not step up to forged connecting rods?

A forged connecting rod is hot-formed from a steel billet (typically 4340) under very high pressure, which makes it far denser and more homogeneous than a production rod. Compared with an original rod (often sintered metal, optimised for series cost), a forged 4340 rod shows about +19% yield strength, +8% tensile strength and, above all, +19% to +37% fatigue strength — meaning a fatigue life several times longer under cyclic load. It is the foundation of a reliable high-power build. For your engine: