ARP reinforced crankshaft main studs for Toyota 20R 22R

The Toyota engines concerned

The 20R (2.2 litres) and the 22R (2.4 litres) are Toyota eight-valve four-cylinder petrol engines. They power the Toyota Celica, Corona, Hilux, 4Runner and Land Cruiser II (Bundera), among others.

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 suffer brinelling, then the bearing bore goes out of round.

This kit replaces the original main cap bolts with 12 mm ARP 8740 steel studs, with their nuts and washers as the ARP instruction sheet lists them. The studs are screwed into the block by hand and the caps are fitted afterwards; threads, nuts and washers receive ARP assembly lubricant before the nuts are torqued in three passes. Preload is higher and more consistent than with the original bolts, and the block threads are spared.

Material: 8740, a chrome-moly steel that ARP specifies at 200,000 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. On this four-cylinder engine, the 8740 studs in M12 are rated for 1,200 hp at most (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.

The nuts are tightened in the sequence the manufacturer specifies for the main caps; the instruction sheet supplied with the kit describes the full procedure.

Stronger fasteners change the clamping force: the size and roundness of the main bearing bores are checked after installation, and the bores are align honed if necessary, using the final fasteners and lubricant.

The torque figures above come from the ARP 203-5406 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 203-5406 instruction sheet

Technical guide

All the torque values on this page assume ARP assembly grease; with engine oil they are no longer correct.

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	ARP studs
Tightening	Bolt turned straight into the block	Nuts tightened in three passes, gradual build-up
Block threads	Loaded every time the bolt turns	Stud screwed in by hand, no torque load
Fitting the caps	Cap held by hand while the bolts go in	Cap guided by the two studs

When studs become necessary

• Power increase from a turbo, supercharger or higher boost
• Stroker crankshaft or higher rev limit
• Complete bottom end strip-down
• Bearing bores or block threads already fatigued
• Intensive motorsport use

Vehicle compatibility

Why is it the most cost-effective solution?

On a tuned 20R or 22R, 12 mm ARP 8740 studs hold the main caps more firmly than the original bolts and reduce the risk of bottom-end damage. Their price stays modest next to the cost of rebuilding a crankshaft and a block.