Reinforced ARP main studs for Audi S2 RS2 S4 2.2T 20V

The VAG engines concerned

This kit is made for the Volkswagen Group inline five-cylinder turbo of 2.2 litres and 20 valves (codes 3B, AAN, ABY and ADU), fitted to the Audi S2, S4 C4 and RS2.

As standard, the crankshaft main caps are secured by main cap bolts screwed into the block. The reference of this original bolt is not published in our manufacturer data: this kit replaces it with ARP studs and nuts.

Reinforced ARP studs for main bearings

On a crankshaft, the main caps are what hold the shaft against the loads passed on by the connecting rods. If their clamping force drops, the cap shifts slightly on its parting line at every cycle: the mating faces become indented, then the bearing bore goes out of round.

This kit replaces the original main cap fasteners with 10 mm ARP studs in 8740 steel and their nuts. Each stud is screwed into the block by hand; the caps are then fitted, threads, nuts and washers receive the ARP Ultra-Torque lubricant provided, and the nuts are torqued in three passes, in the manufacturer's sequence. Tightening becomes more even, preload rises and the block threads are no longer stressed by the turning of the bolt. Material: 8740, a chrome-moly steel that ARP specifies at 200,000 psi tensile strength, with threads rolled after heat treatment. Factory-fitted fasteners usually belong to classes 10.9 and 12.9, with 150,800 to 176,900 psi minimum tensile strength. On this turbo five-cylinder engine, the 8740 studs in M10 are rated for 1,200 hp at most (calculated estimate).

Technical specifications

Tightening torque

No torque is applied to the stud as it goes into the block: it is screwed in by hand. For a permanent installation, the instruction sheet leaves the option of a thread locker of the blue Loctite type on the block end, with the nuts fully tightened before it cures, never on the nuts and never mixed with ARP grease.

The nuts are tightened following the order set by the manufacturer for the caps; every step is given in the ARP instruction sheet.

With stronger fasteners, the clamping force is no longer what it was originally: the size and roundness of the main bearing bores must be checked once installation is complete, and the bores line-honed if necessary with the final fasteners and lubricant.

The torque figures above come from the ARP 204-5404 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 204-5404 instruction sheet

Technical guide

All the torque values on this page assume ARP assembly grease; with engine oil they are no longer correct.

The ARP brand

Coming from the aerospace industry, Gary Holzapfel founded ARP (Automotive Racing Products) in the early 1970s to put an end to engine failures caused by weak fasteners in motorsport. The company designs and manufactures thousands of part numbers in California, in several material grades depending on the application.

Advantages over the original bolts

Criterion	Original main bolts	Reinforced ARP studs
Tightening method	Bolt turned into the block	Nuts tightened progressively, in three passes
Block thread	Loaded by the turning bolt	Stud placed by hand, no torque load
Refitting the caps	Cap to be held while screwing	Cap positioned by the studs

When studs become necessary

• Power increase from a turbo, supercharger or higher boost
• Stroker crankshaft or higher rev limit
• Complete bottom end strip-down
• Bearing bores or block threads already fatigued
• Intensive motorsport use

Vehicle compatibility

Why is it the most cost-effective solution?

On a 2.2 litre turbo five-cylinder tuned beyond its original output, ARP 8740 steel studs, stronger than the original fasteners, clamp the main caps more firmly and reduce the risk of bottom-end failure. Their price stays moderate next to the cost of rebuilding a crankshaft and a block.

Consider the crankshaft main bearings

When the bottom end is open, the bearings are replaced too. Here are the tri-metal crankshaft main bearings designed for these engines: