Reinforced ARP bolts and nuts for OEM rods ALFA ROMEO 06224 105

The Alfa Romeo 2.0 eight-valve engines concerned

This kit is meant for the 2.0 litre eight-valve Alfa Romeo engine with code 06224, fitted to the Alfa 75 2.0 T.S. (146 and 148 hp, from 1985 to 1992), and to the Alfa Romeo GTV 2.0 with code 105 named by ARP (GT V 2000, 131 hp, from 1971 to 1977).

This ARP kit replaces the original rod bolts of these engines, whose part number is not published. ARP lists it as a set of M10 x 1.25 bolts pressed into the rods, with their nuts, for the Alfa Romeo 2.0 GTV.

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.

These 8740 bolts are pressed into the rods and then receive their nuts. ARP recommends checking the stretch, 0.190 to 0.203 mm; without a gauge, its instruction sheet specifies 61 Nm. 8740 is a chrome-moly steel that ARP heat treats to 180,000 psi tensile strength, with threads rolled after heat treatment. As a reference point, standard engine fasteners mostly belong to classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum strength. In 8740, these bolts are rated for 11,000 rpm at most (calculated estimate).

Technical specifications

Tightening torque and stretch

ARP gives priority to stretch control for an accurate preload; the torque in the table is used only when no gauge is available. Torque and stretch figures in the table apply with ARP lubricant.

Source of the torque and stretch figures: ARP 126-6101 instruction sheet, in the revision applicable at publication. The manufacturer's instruction sheet prevails in the event of any difference. Read the ARP 126-6101 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 their threads and 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

Tightening is done with ARP assembly grease, on the bolt threads and on the bearing face of the nuts: 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

Why is it the most cost-effective solution?

On a prepared Alfa 75 or GTV, each rod bolt takes a tension that climbs with engine speed, and a single bolt letting go ruins the rod, the piston and the block. The extra cost of an 8740 kit weighs little next to a complete rebuild of the bottom end.