Reinforced ARP bolts and nuts for OEM rods PORSCHE 911 2.4 2.7 3.0 930

The Porsche 911 engines concerned

This kit is for the twelve-valve six-cylinders of the first-generation Porsche 911: the 2.4-litre (2,341 cc, listed as 2.3 in vehicle catalogues, 130 to 190 hp, 1971 to 1973), the 2.7-litre (2,687 cc, 150 to 209 hp, 1972 to 1979) and the 3.0-litre, naturally aspirated or turbo (2,993 cc, 180 to 260 hp, 1974 to 1983), in Coupe, Targa and Convertible bodies.

The original rod bolt of these engines has no published diameter or reference; this M10 ARP kit replaces it, and the maker presents it for the Porsche 911.

Reinforced ARP bolts and nuts 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.

The ARP 204-6001 kit is made of ARP2000. The instruction sheet asks for the bolt stretch to be measured, 0.241 to 0.254 mm, and gives a 67.8 Nm torque only when no gauge is at hand. 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 ARP2000 bolts hold up to 11,750 rpm (calculated estimate).

Technical specifications

The ARP instruction sheet has the bolts pressed into the rods, the caps fitted and the nuts tightened by stretch; the rod bore must have a chamfer that clears the radius under the bolt head.

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 204-6001 instruction sheet, revision in force on the day of publication. Should any difference appear, the official instruction sheet takes precedence. Read the ARP 204-6001 instruction sheet

Assembly is done without thread locker, as the ARP instruction sheet calls for none: ARP Ultra-Torque grease is applied to the threads of each bolt and to the bearing face of its nut.

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

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

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 classic 911 that is pushed to high revs or boosted, each rod bolt sees a pull that grows with engine speed. A single bolt letting go takes the rod, the crankcase and the crankshaft with it: replacing the bolts before a failure costs much less than rebuilding the 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.