Reinforced ARP bolts and nuts for OEM rods BMW M10B20

The BMW engine concerned

The BMW M10B20 is the 2.0-litre version (89 mm bore, 80 mm stroke) of BMW's eight-valve inline four-cylinder. It sits under the bonnet of the 2000 and 2002, Turbo included, as well as the 320 (E21) and 520 (E12).

The original rod bolt of the M10B20 is a bolt with reference 11 24 1 719 991, tightened by a nut with reference 11 24 0 518 321 (M10 x 1): BMW requires replacing the bolt and nut each time they are removed, washing and oiling them, then tightening to 55 Nm.

Reinforced ARP bolts and nuts for connecting rods

Few parts of the bottom end work as hard as the rod bolt: at every revolution, it is what stops the cap from pulling away under the inertia loads of the rod and piston assembly. The original bolt is designed for stock power.

This kit replaces the original bolt and nut of each rod with an ARP2000 press-fit bolt and a nut, which the ARP instruction sheet has you tighten by stretch measured with a gauge, the 67.8 Nm torque being used only when no gauge is available. ARP2000 is an alloy steel developed by ARP and heat treated to 220,000 psi tensile strength; its threads are rolled after heat treatment. Standard engine fasteners commonly fall into classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum strength: ARP2000 sits 24 to 46% above that. The engine speed allowed by the ARP2000 bolts goes up to 11,750 rpm (calculated estimate).

Technical specifications

The ARP instruction sheet requires chamfering the entry of the rod bore before the bolt is pressed in, to clear the radius under its head.

Tightening torque and stretch

For this part, ARP favours tightening to a measured stretch, the key to an exact preload; torque is given only when no gauge is available. The figures in the table assume ARP lubricant.

Source of the torque and stretch figures: ARP 201-6304 instruction sheet, in the revision applicable at publication. The manufacturer's instruction sheet prevails in the event of any difference. Read the ARP 201-6304 instruction sheet

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

According to the ARP instructions, the big ends must be checked and resized with the fasteners in place; plan a visit to 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

All the torque and stretch values on this page assume ARP assembly grease on the bolt threads and on the bearing face of the nuts; engine oil does not replace it.

The ARP brand

An engineer with an aerospace background, Gary Holzapfel launched ARP (Automotive Racing Products) in the early 1970s with one goal: to eliminate engine failures caused by weak fasteners in racing. ARP designs and manufactures thousands of part numbers in California, cylinder head, main and rod bolts, in several materials depending on the use, and has become known for the consistency of its manufacturing.

Vehicle compatibility

OEM reference (rod bolt): 11 24 1 719 991 (M10 x 1, nut 11 24 0 518 321)

Why is it the most cost-effective solution?

On an M10B20 pushed to higher revs, or turbocharged as the factory 2002 Turbo was, the rod bolts see ever greater tensile loads, and the failure of a single one wrecks the rod, the piston and the block. ARP2000 bolts secure this point for far less than rebuilding a bottom end.

Matching connecting rod bearings

Removing the connecting rods is the right time to replace their bearings: here are the ones that fit 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: