Reinforced ARP bolts and nuts for OEM rods PORSCHE 911 2.0 2.2 901 911

The Porsche 911 engines concerned

This kit is for the twelve-valve six-cylinders of the earliest Porsche 911 models: the 2.0-litre (1,991 cc, 110 to 170 hp, 1963 to 1972) and the 2.2-litre (2,195 cc, 125 to 180 hp, 1969 to 1972), in Coupe and Targa bodies.

For the original rod bolt of these engines, neither diameter nor reference is published; this ARP kit takes its place, and the maker lists it for the Porsche 911 2.0 S of 1969.

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.

The ARP 204-6003 kit is made from ARP2000. ARP recommends tightening each nut until the bolt has stretched between 0.229 and 0.241 mm; the 67.8 Nm torque is only provided for when no gauge is available. 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%.

Technical specifications

According to the ARP instruction sheet, the bolts are pressed into the rods; once the caps are fitted, the nuts are tightened by stretch. A chamfer must clear the radius under the bolt head in the rod bore.

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 204-6003 instruction sheet, revision in force on the day of publication. Should any difference appear, the official instruction sheet takes precedence. Read the ARP 204-6003 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.

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

Stretch measurement supplements torque tightening and gives the most accurate preload. It is done with the bolt in place: the gauge, fitted with a dial indicator, bears on both ends of the bolt and shows the stretch achieved, to be brought to the value in the table above. This avoids the variations caused by friction, which matters on a highly stressed engine.

Technical guide

Torque and stretch figures are only valid with ARP assembly grease, applied to the bolt threads and to the bearing face of the nuts.

The ARP brand

ARP (Automotive Racing Products) came into being in the early 1970s, when Gary Holzapfel, who came from the aerospace industry, decided to tackle the engine failures caused in motorsport by inadequate fasteners. Today the brand produces thousands of part numbers in California for the cylinder head, the main bearings and the connecting rods, in materials suited to each application, with manufacturing known for its consistency.

Vehicle compatibility

Why is it the most cost-effective solution?

On a 911 built before 1973 whose engine is being rebuilt, the original rod bolts are more than fifty years old. A single bolt that breaks destroys the rod, the crankcase and the crankshaft: replacing them during the rebuild costs far less than redoing the whole engine.

Matching connecting rod bearings

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