Reinforced ARP main bolts for SUBARU EJ20 EJ22 EJ25

The Subaru EJ engines concerned

ARP lists this part number for the four-cylinder Subaru EJ engine family of 2.0, 2.2 and 2.5 litres, with single or double overhead camshafts. The compatibility table covers the EJ20, EJ22 and EJ25 codes and their EJ205, EJ207, EJ255 and EJ257 variants, taken from the NGK parts catalogue.

These engines are flat-four units whose main bearing caps are clamped by bolts passing through the crankcase; this kit replaces that original hardware, whose factory part number is not published for the whole family and is therefore not shown here.

Reinforced ARP bolts for main bearings

Each main bearing takes a share of the loads the connecting rods pass on at every combustion. Pulled downwards, the main cap tends to slide on its parting line: over time the mating faces brinell and the bearing bore loses its shape.

This kit brings together ARP bolts for the crankshaft main bearings, listed in the ARP catalogue among the crankcase through-bolt kits, with 10 mm and 8 mm bolts. The instruction sheet calls for the threads and heads to be lubricated with ARP Ultra-Torque lubricant, for the original sealing washers to be kept, and for the chamfered washers, chamfer facing the bolt head, to be fitted on the 10 mm bolts concerned. The instruction sheet does not state the number of pieces. The material is Inconel 718, a nickel-based alloy: the ARP catalogue gives it a tensile strength of 210,000 to 230,000 psi and describes it as immune to hydrogen embrittlement and corrosion. The Inconel bolts in M10 and M8 hold up to 1,000 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

The bolts pass through the cap and are tightened straight into the block, to torque and in stages, with threads and underside of the head lubricated with ARP grease.

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 align honed if necessary with the final fasteners and lubricant.

Torque figures taken from the ARP 260-5401 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 260-5401 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

• Subaru EJ engine built to go well beyond its standard output
• Crankcase opened to fit a forged crankshaft, rods or pistons
• Main bearing bores to be checked, and reworked if needed, before fitting reinforced fasteners
• Sustained rally, circuit or competition use at high revs
• Complete bottom-end rebuild with replacement of the main cap fasteners

Vehicle compatibility

Why is it the most cost-effective solution?

A Subaru EJ engine pushed beyond its standard output puts heavy loads on the bottom end. An ARP Inconel bolt kit costs little compared with a crankcase to rework and a crankshaft to replace.