Reinforced ARP main studs for Honda and Acura B18A1 B18B1

The Honda and Acura engines concerned

This kit is intended for the 1.8-litre 16-valve Honda and Acura four-cylinders, the B18A1 and B18B1, as per the application given by ARP. They power the Integra DA9 and DC2.

On these engines as built, the main caps are held by bolts (Honda part number 90006-P8A-A01); this kit replaces them with 7/16 in studs.

Reinforced ARP studs 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 replaces the original main cap bolts with 7/16 in ARP studs in 8740. Once the block threads are cleaned, the studs are screwed in by hand only, then the caps are fitted. ARP Ultra-Torque lubricant goes on the threads, the washers and the nuts, which are then tightened in three equal passes, to 36, 72 then 108 Nm, in the manufacturer's order. ARP rules out engine oil, whose friction upsets the clamping force. 8740 is a chrome-moly steel heat treated by ARP to 200,000 psi tensile strength, with threads rolled after heat treatment. To put this figure in context, standard engine fasteners mostly belong to property classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum tensile strength. These 8740 studs in 7/16 in take up to 1,200 hp on this four-cylinder engine (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.

ARP instruction sheet 208-5404, titled installation method for main stud kits, sets 80 ft-lb in three equal passes, i.e. 108 Nm.

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 align honed if necessary with the final fasteners and lubricant.

Torque figures taken from the ARP 208-5404 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 208-5404 instruction sheet

Technical guide

The torque figures given only apply with ARP assembly grease, never with engine oil.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set out to prevent fastener-related engine failures in motorsport. Its thousands of part numbers are designed and manufactured in California, in materials chosen for each use.

Advantages over the original bolts

Criterion	Original main bolts	Reinforced ARP studs
Assembly	The bolt turns in the block thread during tightening	The stud stays still, only the nut turns
Condition of the block threads	Worn by every screwing of the bolt	Spared: the stud is placed by hand
Seating the caps	Cap to be held while screwing	Cap guided by the studs

When studs become necessary

• B18A1 or B18B1 built to rev higher
• Power beyond the standard output
• Bottom end stripped for a rework
• Loosened main caps or worn block threads
• Sporty road use, track or competition

Vehicle compatibility

OEM reference: 90006-P8A-A01

Why is it the most cost-effective solution?

On a B18A1 or B18B1 pushed for revs or power, the main caps work harder than the standard fasteners were designed for. Replacing the bolts with these ARP studs costs far less than reworking a block whose bearing bores have distorted.

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: