Reinforced ARP2000 rod bolts BMW M20 M42 M50 M70 M73 S70

The compatible BMW engines

BMW built a strong reputation for reliability with its 1980s and 1990s petrol engines. The M20 inline-six, with a single overhead camshaft and 12 valves, powered the 325e and 325i (2.7 and 2.5 litres) into the early 1990s. It gave way to the M50, BMW's first mass-produced twin-cam 24-valve six (1990), in 2.0 and 2.5 litres, gaining intake VANOS on the M50TU version (1992). The M42 four-cylinder (1.8 litre, 16-valve) rounded out the range in the 318is and 318ti.

At the top, BMW introduced its first production V12 in 1987, the M70 (5.0 litres, 24 valves), fitted to the 750i (7 Series E32) and 850i (8 Series E31). It later evolved into the M73 (5.4 litres) in the 750i E38 and 850Ci, while the high-performance S70 (5.6 litres), developed by the M division, powered the exclusive 850CSi.

Reinforced ARP rod bolts

The rod bolt is one of the most heavily loaded parts of the bottom end: at every cycle it absorbs the inertial forces of the rod-and-piston assembly. These engines share the same original bolt, 9 mm in diameter and 53 mm in usable length (BMW reference 11 24 1 713 342), sized for the standard power output.

As soon as a build raises cylinder pressure and engine speed, this bolt reaches its limit. This kit replaces it with ARP2000 Pro Series 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 preload by stretch measurement, which ensures an accurate clamp load.

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 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.

How to choose your fasteners?

The rod bolt is one of the most heavily loaded parts of the engine. The key is to match the ARP grade to the build's actual use, then to strictly follow the tightening torque and stretch.

ARP 2000 (tensile strength ~220,000 psi, i.e. ~1,517 MPa) is the high-performance standard. It is the most common grade for circuit, trackday, drift, rally, drag and hillclimb, valued for its strength, reliability and versatility, with no particular storage constraints.

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?

For a fraction of the cost of a repair, this kit protects a bottom end whose rebuild runs into thousands of euros. If an original rod bolt gives way, the connecting rod breaks free and destroys the crankshaft and the block. Fitting ARP bolts during an engine teardown removes this risk: it is one of the most cost-effective safeguards of any build.