Reinforced ARP bolts for OEM rods BMW TOYOTA M52 M54 N20 N54 N55 B58

The BMW engines concerned

This kit covers twelve BMW engine codes: the naturally aspirated six-cylinder M52 (2.5 and 2.8 litres) and M54 (2.5 and 3.0 litres), the 2.0-litre turbocharged four-cylinders N20, N26, B46 and B48, and the 3.0-litre turbocharged six-cylinders N54, N55, S55 and B58. They power the 3 Series from the E36 to the G20, along with the 1, 2, 4, 5, 6, 7 and 8 Series, the X models, the Z3 and the Z4, from 1995 to 2025.

The original rod bolt of these engines carries reference 11 24 7 589 671 (M9 x 47), replaced by 11 24 8 657 724 (M9 x 1.25 x 47) on recent B48 and B58 engines. BMW calls for new bolts, washed and oiled: tightening to 5 Nm, then 20 Nm, then 70 degrees on the M52 and M54, and 20 Nm then 70 degrees on the N54, which makes each original bolt a single-use part.

Reinforced ARP bolts for connecting rods

At every engine revolution, the rod and piston assembly pulls on the rod cap, and only its bolts hold it against these inertia loads. The original ones are intended for stock power and for a single installation.

This kit replaces the original bolts with 47 mm ARP2000 bolts, tightened by stretch, the method ARP recommends, or by torque when no gauge is available. Material: ARP2000, an alloy steel developed by ARP, heat treated to 220,000 psi tensile strength, with threads rolled after heat treatment. Against classes 10.9 and 12.9 of original fasteners, between 150,800 and 176,900 psi minimum, the margin is 24 to 46%. The engine speed allowed by the ARP2000 bolts goes up to 10,250 rpm (calculated estimate).

Technical specifications

Tightening torque and stretch

ARP recommends tightening to a measured stretch, which gives a more accurate preload than torque alone, given as a fallback. Torque and stretch figures assume ARP lubricant.

Figures taken from the ARP 201-6303 instruction sheet, revision in force on the day of publication. Should any difference appear, the official instruction sheet takes precedence. Read the ARP 201-6303 instruction sheet

The ARP instruction sheet does not require a thread locker for this kit; only ARP Ultra-Torque grease is applied, on the threads as well as under the bolt head.

Once the fasteners are fitted, the ARP instructions call for the big ends to be checked and resized by a machine shop.

Measuring bolt stretch

Tightening to stretch means setting the preload on how much the bolt actually stretches, rather than on a torque affected by friction. With the bolt fitted, the dial gauge is placed on both its ends and the bolt is tightened until the stretch given in the table is read. It is the safest method on a highly tuned engine.

Technical guide

Tightening is done with ARP assembly grease, on the threads and under the head: the torque and stretch figures in the table were established with it.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace sector, ARP (Automotive Racing Products) was born to put an end to fastener-related engine failures in racing. Its thousands of part numbers, designed and manufactured in California for the cylinder head, the main bearings and the connecting rods, come in several materials depending on the application and are recognised for the consistency of their manufacture.

Vehicle compatibility

OEM reference (rod bolt): 11 24 7 589 671 (M9 x 47); 11 24 8 657 724 (M9 x 1.25 x 47, recent B48 and B58)

Why is it the most cost-effective solution?

As original equipment, the rod bolt is tightened by torque then angle up to its yield point, which stretches it permanently. In ARP2000, the ARP bolts, reinforced and stronger, accept clearly higher engine speeds and inertia loads: less risk of a fastener-related failure, and therefore an engine repair far more expensive than the kit avoided.

Matching connecting rod bearings

New bolts, new bearings: find below the connecting rod bearings suited to this engine.

Why not step up to forged connecting rods?

A forged rod, hot formed under high pressure from a steel such as 4340, gains density and homogeneity compared with a stock rod. Where the original rod, often made of sintered metal, is aimed first at cost, a 4340 forged rod shows about +19% yield strength, +8% tensile strength and +19 to +37% fatigue strength. It is the cornerstone of a solid high-power build. For your engine: