Reinforced ARP main studs for AUDI five-cylinder engines

Audi five-cylinder engines

ARP lists this kit for "Audi 5-cylinder" engines, with no engine code, model or year given: it is meant for the marque's in-line five-cylinders. Part number 204-5409 is specific to this application.

On these engines, the crankshaft main caps are held by the studs in the kit, in place of the original fasteners.

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 brinell, then the bearing bore goes out of round.

This kit contains ARP 8740 steel studs for the main caps of Audi five-cylinder engines, to be tightened with nuts. ARP makes these fasteners in 8740, a chrome-moly steel brought by heat treatment to 190,000 psi tensile strength; the threads are rolled once the treatment is complete. As a reference point, an engine's original fasteners generally fall into classes 10.9 and 12.9, whose minimum ranges from 150,800 to 176,900 psi. The kit strengthens the main cap fastening of a modified Audi five-cylinder; no strength figure is published for this part number.

Technical specifications

Tightening torque

Technical guide

For assembly, use the ARP assembly grease intended for the purpose rather than engine oil.

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
Fastening method	Bolts tightened one by one into the block thread	Studs fixed in the block, nuts tightened on the cap side
Cap position	Cap brought in by hand, then tightened	Cap slid over the studs, already aligned when fitted
Material	Manufacturer's original steel	Chrome-moly steel, grade 8740

When studs become necessary

• Audi five-cylinder build for track, rally or drag use
• Turbocharged or supercharged five-cylinder pushed far beyond stock output
• Bottom end opened up to change the crankshaft or rods
• Forged pistons or stronger rods fitted to a production block
• Cap fasteners to be made reliable before race entries

Vehicle compatibility

Why is it the most cost-effective solution?

A tuned five-cylinder loads its main bearings harder. 8740 ARP studs cost little compared with a crankshaft and a block to replace.