Reinforced ARP main studs for Mitsubishi 4G54 (G54B)

The Mitsubishi engine concerned

This kit is for the Mitsubishi 4G54 (G54B) 8-valve four-cylinder, a 2.6-litre according to ARP. It is found in the Pajero (Montero), the L200 (Triton) and the Sigma (Magna).

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 12 mm ARP studs in 8740 steel. Once the block threads are cleaned, the studs are screwed in by hand, then the caps are fitted. Shanks, washers and nuts receive the ARP lubricant supplied, and the nuts are tightened in three equal passes, in the order set by the manufacturer, to 41, 81 then 122 Nm. ARP advises against engine oil, whose friction distorts the clamping obtained.

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 12 mm 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 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 207-5402 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 207-5402 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 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

• 4G54 rebuilt to take more revs
• Power above the standard output
• Bottom end opened for a rebuild
• Main caps with play or tired block threads
• Sustained sporting or off-road use

Vehicle compatibility

Why is it the most cost-effective solution?

When a 4G54 is rebuilt to take more revs or more power, the main caps carry loads that the original fasteners were not designed to absorb. These 12 mm ARP studs steady the clamping for a modest outlay compared with a block to be reworked.