Reinforced ARP main studs for Ford Duratec 2.0 2.3

The Ford and Mazda engines concerned

This kit fits the Ford Duratec four-cylinder engines of 2.0 and 2.3 litres, 16 valves and twin overhead camshafts, also built by Mazda as the LF and L3, found in particular in the Focus, Mondeo, Fiesta ST, Mazda 3, Mazda 6 and MX-5.

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.

The ARP 8740 steel studs in this kit, in M10, replace the original main cap fasteners of the Duratec. After cleaning the block threads, they are screwed in by hand, without a wrench. With the caps fitted, threads, nuts and washers are greased with the ARP Ultra-Torque lubricant supplied, then the nuts are tightened in three equal passes in the manufacturer's order. Only the nut turns: the torque reading therefore reflects the real preload better, and the block thread is not twisted.

ARP makes these fasteners in 8740, a chrome-moly steel brought by heat treatment to 200,000 psi tensile strength; the threads are rolled once the treatment is complete. As a reference point, an engine's original fasteners generally fall into classes 10.9 and 12.9, whose minimum ranges from 150,800 to 176,900 psi. These 8740 studs in M10 take up to 1,000 hp on this four-cylinder engine (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.

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

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.

Torque figures taken from the ARP 151-5405 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 151-5405 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 screwed into the block, turning under torque	Nut alone turns, tightened in three passes
Block thread	Takes the rotation of the bolt at each assembly	Stud placed by hand, no effort
Positioning the caps	Cap to be held while screwing	Cap guided by the studs

When studs become necessary

• Duratec 2.0 or 2.3 boosted by a turbo or supercharger
• Engine speed or power well above the original
• Bottom end stripped for a rebuild
• Main caps that move or tired block threads
• Repeated sporting use, track, rally or drag

Vehicle compatibility

Why is it the most cost-effective solution?

A Duratec pushed well above its original output, through a turbo, a supercharger or high revs, asks more of the main caps than the standard fasteners can hold. These ARP studs provide a much higher preload for a modest cost, far below that of a bottom end to rebuild.