Reinforced ARP bolts and nuts for OEM rods MITSUBISHI 4G63 6-bolt

The Mitsubishi 4G63 6-bolt engine concerned

This kit is intended for the Mitsubishi 4G63 2.0-litre engine, a four-cylinder with twin overhead camshafts and 16 valves, in the 6-bolt version that ARP declares for engines of 1993 and earlier: first-generation Eclipse, Talon, Laser and Galant VR-4.

It replaces the original rod bolt with an ARP 8740 bolt of M9 diameter, pressed into the connecting rod and closed with a nut.

Reinforced ARP bolts and nuts for connecting rods

Few parts of the bottom end work as hard as the rod bolt: at every revolution, it is what stops the cap from pulling away under the inertia loads of the rod and piston assembly. The original bolt is designed for stock power.

Pressed into each stock 6-bolt 4G63 rod and closed by a nut, these bolts are tightened by stretch, read on a gauge, as ARP recommends; ARP also states a fallback torque for when no gauge is at hand. 8740 is a chrome-moly steel that ARP heat treats to 180,000 psi tensile strength, with threads rolled after heat treatment. As a reference point, standard engine fasteners mostly belong to classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum strength. In 8740, these bolts are rated for 9,500 rpm at most (calculated estimate).

Technical specifications

The ARP instructions require a sufficient chamfer at the top of the rod bore to clear the radius under the bolt head before the bolts are fitted.

Tightening torque and stretch

ARP recommends tightening to a measured stretch, which gives a more accurate preload than torque alone, given as a fallback. Torque and stretch figures assume ARP lubricant.

The values above come from the ARP 107-6001 instruction sheet applicable at the date of publication; it is authoritative in the event of any difference. Read the ARP 107-6001 instruction sheet

No thread locker is called for by the ARP instruction sheet for this kit: the bolts are fitted with ARP Ultra-Torque grease, on their threads and on the bearing face of the nuts.

Once the fasteners are fitted, the ARP instructions call for the big ends to be checked and resized by a machine shop.

Measuring bolt stretch

With the stretch gauge, you read directly how much the bolt stretches during tightening: the dial gauge sits on both ends of the fitted bolt, and tightening stops when the stretch reaches the value in the table. Friction no longer comes into play, hence a more consistent preload on a heavily stressed engine.

Technical guide

Torque and stretch figures are only valid with ARP assembly grease, applied to the bolt threads and to the bearing face of the nuts.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace sector, ARP (Automotive Racing Products) was born to put an end to fastener-related engine failures in racing. Its thousands of part numbers, designed and manufactured in California for the cylinder head, the main bearings and the connecting rods, come in several materials depending on the application and are recognised for the consistency of their manufacture.

Vehicle compatibility

Why is it the most cost-effective solution?

On a 4G63 turbo whose boost pressure and engine speed are being raised, the rod bolts take ever higher tensile loads, and a single failure ruins the rod, the piston and the block. An ARP 8740 kit protects this point for a much smaller outlay than rebuilding a bottom end.

Matching connecting rod bearings

Removing the connecting rods is the right time to replace their bearings: here are the ones that fit this engine.