Reinforced ARP bolts for OEM rods BMW S14B20 S14B23 S14B25

The BMW engines concerned

The BMW S14 is the 16-valve inline four-cylinder petrol engine of the M3 (E30) and the 320is. It comes in 2.0 litres (S14B20, 192 hp), 2.3 litres (S14B23, 200 and 215 hp) and 2.5 litres (S14B25, 238 hp).

The original connecting rod bolt of the S14 carries the reference 11 24 1 307 140: BMW prescribes replacing it each time it is removed, washing and oiling it, then tightening it to 55 Nm.

Reinforced ARP bolts 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 and is single-use.

This kit replaces the original bolts of the four rods with ARP2000 bolts, tightened by measuring stretch, the method ARP recommends for this part, or failing that by torque. These bolts are made from ARP2000, an ARP-specific alloy steel heat treated to 220,000 psi tensile strength, with threads rolled once the treatment is complete. Classes 10.9 and 12.9 of standard fasteners start at 150,800 and 176,900 psi: ARP2000 exceeds them by 24 to 46%. The ARP2000 bolts hold up to 13,500 rpm (calculated estimate).

Technical specifications

Tightening torque and stretch

For this part, ARP favours stretch measurement in addition to torque, the key to an exact preload. The figures in the table assume ARP lubricant.

The values above come from the ARP 201-6104 instruction sheet applicable at the date of publication; it is authoritative in the event of any difference. Read the ARP 201-6104 instruction sheet

No thread locker is called for by the ARP instruction sheet for this kit: the bolts are fitted with ARP Ultra-Torque grease, on the threads and under the 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

With the stretch gauge, you read directly how much the bolt stretches during tightening: the dial gauge sits on both ends of the fitted bolt, and tightening stops when the stretch reaches the value in the table. Friction no longer comes into play, hence a more consistent preload on a heavily stressed engine.

Technical guide

All the torque and stretch values on this page assume ARP assembly grease on the threads and under the bolt head; 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 1 307 140

Why is it the most cost-effective solution?

Replacing the original bolts, which have to be changed each time the rods are removed anyway, with stronger ARP2000 bolts whose preload is set by measuring stretch costs a fraction of the price of an engine repair after a rod failure.

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 connecting rod starts as a steel billet, usually 4340, shaped hot under very high pressure: its material is denser and more homogeneous than that of a stock rod. Compared with an original rod, often made of sintered metal and designed for cost, a 4340 forged rod offers about +19% yield strength, +8% tensile strength and +19 to +37% fatigue strength. It is the foundation of a reliable high-power build. For your engine: