Reinforced ARP main studs for Mitsubishi 4G63 and 4G64

The Mitsubishi engines concerned

This kit is for the Mitsubishi 4G63 2.0-litre 16-valve four-cylinder, in both 6-bolt and 7-bolt versions, and for the 2.4-litre 4G64, as declared by ARP. They are found in the Eclipse and Talon, the Galant VR-4 and the Lancer Evolution.

On this block, the manufacturer secures the main caps with bolts; this kit fits studs in their place.

Reinforced ARP studs for main bearings

The bottom end rests on its main bearings: combustion after combustion, the loads coming from the connecting rods end up on them. Under this stress the main cap tries to move on its parting line, which eventually brinells the mating faces and distorts the bearing bore.

This kit replaces the original main cap fasteners with 10 mm ARP studs in 8740 steel. The block is cleaned, the studs are screwed in by hand, then the caps are fitted. Washers and threads then receive the ARP lubricant supplied, and the 12-point nuts are tightened in three equal passes, in the order set by the manufacturer, to 27, 54 then 81 Nm. ARP advises against engine oil, whose friction distorts the clamping obtained. 8740 is a chrome-moly steel heat treated by ARP to 200,000 psi tensile strength. 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 10 mm take up to 1,000 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Fitting the studs: screwed into the block by hand, without a tightening tool. A Loctite thread locker may be used for a permanent installation according to the ARP instructions; tightening must then be completed before the product hardens.

The nuts are tightened following the order set by the manufacturer for the caps; every step is given in the ARP instruction sheet.

Moving to reinforced fasteners changes the clamping force on the caps. After installation, the size and roundness of the bores are checked, then the bores are line-honed if needed, always with the final fasteners and lubricant.

Torque figures taken from the ARP 207-5401 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 207-5401 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.

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

• Turbo 4G63 tuned for more boost
• Power well above the standard output
• Bottom end opened for a rebuild
• Main caps with play or tired block threads
• Repeated sporting use, track, rally or drag

Vehicle compatibility

Why is it the most cost-effective solution?

On a 4G63 turbo pushed towards more boost or higher revs, the main caps work harder than the original fasteners were designed to withstand. These ARP studs steady the clamping for a cost that bears no relation 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: