Reinforced ARP main bolts for PORSCHE 3.4 3.6

The water-cooled Porsche engines concerned

ARP lists this part number for naturally aspirated, water-cooled Porsche engines of 3.4 to 3.6 litres, and its catalogue ties it to the 3.4-litre 911 (996): a flat-six whose crankshaft main caps are secured by bolts tightened into the block.

The original Porsche main bearing fasteners are replaced by this ARP bolt kit; their factory part number is not published in our sources and is therefore not shown here.

Reinforced ARP bolts for main bearings

In a bottom end, the main bearings absorb the thrust of the connecting rods at every combustion, and it is the main caps, clamped to the block, that hold the crankshaft in place. When their clamping gives way, the cap works on its parting line: the mating faces become marked, then the bearing bore distorts.

This kit contains ARP Pro Series main bolts in 8740 steel for the main caps of this engine. The head and threads are lubricated with ARP Ultra-Torque lubricant, then the bolts are tightened in three equal steps up to 68 Nm (50 ft-lb), in the order prescribed by the manufacturer. ARP does not state the number of pieces for this part number. Material: 8740, a chrome-moly steel that ARP specifies at 190,000 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. The kit replaces the original main bearing fasteners of this engine and is tightened according to the enclosed ARP instruction sheet; no strength figure is published for this part number.

Technical specifications

Tightening torque

Fitting the bolts: through the cap, straight into the block, tightened to torque in successive stages after ARP greasing of the threads and head seats.

The bolts 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 honed in line if necessary with the final fasteners and lubricant.

Torque figures taken from the ARP 204-5001 instruction sheet, in the revision in force on the day of publication. In the event of any difference, the manufacturer's instruction sheet prevails. Read the ARP 204-5001 instruction sheet

Technical guide

Tightening is done with ARP assembly grease: the torque figures in the table were established with it, not with engine oil.

The ARP brand

ARP, short for Automotive Racing Products, was born in the early 1970s on the initiative of Gary Holzapfel, an engineer from the aerospace sector, in response to the engine failures caused in racing by inadequate fasteners. Today the brand produces thousands of part numbers in California, offered in several materials depending on the application.

When to upgrade the main bearing fasteners

• Build of a naturally aspirated, water-cooled Porsche engine going beyond its standard output
• Bottom end opened up to fit a forged crankshaft, rods or pistons
• Main bearing housings to be checked and aligned before fitting stronger fasteners
• Regular track or competition use at high revs
• Main cap fasteners replaced during a complete rebuild

Vehicle compatibility

Why is it the most cost-effective solution?

A Porsche engine that goes beyond its standard output loads its main caps harder. An ARP Pro Series bolt kit costs little compared with a block to line-hone and a crankshaft to replace.