Reinforced ARP main studs for Honda H22A and H23A

The Honda engines concerned

This kit is for the Honda H22A 2.2-litre and H23A 2.3-litre 16-valve four-cylinders, as declared by ARP. They are found in the Prelude and in the Accord Type R.

On the stock H22A the main caps are secured with bolts; this kit replaces them with studs.

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 replaces the original main cap fasteners with 7/16 in ARP studs in 8740 steel. The block threads are cleaned, the studs are screwed in by hand, then the caps are fitted. Threads, washers and nuts receive ARP Ultra-Torque lubricant, and the 12-point nuts are tightened in three equal passes, in the order set by the manufacturer, to 36, 72 then 108 Nm. ARP advises against engine oil: its friction distorts the clamping obtained. 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. On this four-cylinder engine, the 8740 studs in 7/16 in are rated for 1,200 hp at most (calculated estimate).

Technical specifications

Tightening torque

The studs are screwed into the block by hand, with no torque. The ARP instruction sheet allows a thread locker of the blue Loctite type on the block end for a permanent installation, provided the nuts are fully tightened before it sets; never on the nuts, never with ARP grease.

ARP instruction sheet 208-5401 applies to the Honda H22A and H23A and calls for three equal passes up to 80 ft-lb, 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.

The torque figures above come from the ARP 208-5401 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 208-5401 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

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	Bolt turning in the block under torque	Only the nut turns, in three passes
Block thread	Stressed by the bolt rotating at every assembly	Stud placed by hand, no strain
Fitting the caps	Cap to be held while screwing	Cap guided by the studs

When studs become necessary

• H22A or H23A rebuilt to rev higher
• Power above the standard output
• Bottom end opened for a rebuild
• Main caps with play or tired block threads
• Sporting use, track or competition

Vehicle compatibility

Why is it the most cost-effective solution?

On an H22A or H23A rebuilt to rev higher or make more power, the main caps see loads above those the original fasteners must hold. These 7/16 in ARP studs make the clamping steadier for a cost out of all proportion to that of a block to be reworked.

Consider the crankshaft main bearings

A bottom end rebuild calls for new bearings. We offer the tri-metal crankshaft main bearings that match these engines: