Reinforced ARP main studs for Ford Pinto 2.0

The Ford engine concerned

This kit is for the 2.0-litre Ford OHC « Pinto » four-cylinder, 8 valves, a single overhead camshaft engine that powered the Capri, Cortina, Escort RS2000, Granada and Sierra, as well as the P100 pick-up.

Reinforced ARP studs for main bearings

Each main bearing takes a share of the loads the connecting rods pass on at every combustion. Pulled downwards, the main cap tends to slide on its parting line: over time the mating faces brinell and the bearing bore loses its shape.

These ARP 8740 steel studs, 12 mm, replace the original main cap fasteners of the Pinto. After checking the block threads, the studs are fitted hand-tight only. With washers and nuts in place, threads, nuts and washers are lubricated with the ARP Ultra-Torque supplied, then tightened in three equal passes, in the manufacturer's sequence: 40, 81 then 122 Nm. ARP advises against engine oil, which raises friction and makes the clamping force irregular.

8740 is a chrome-moly steel heat treated by ARP to 200,000 psi tensile strength, with threads rolled after heat treatment. 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. The 8740 studs in 12 mm hold up to 1,200 hp on this four-cylinder engine (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.

Follow the cap tightening sequence recommended by the manufacturer when bringing the nuts up to torque; the kit's instruction sheet details each step.

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 151-5401 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 151-5401 instruction sheet

Technical guide

The torque figures given only apply with ARP assembly grease, never 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	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

• Pinto 2.0 built for historic rally, track or drag
• Revs and power well beyond the original
• Block refurbished during a full rebuild
• Main caps that move or tired block threads
• Fitting a forged crankshaft or pistons

Vehicle compatibility

Why is it the most cost-effective solution?

A Pinto built for competition, whether historic rally, track or drag, climbs in revs and power well beyond what Ford planned. The main caps then need a more secure clamp, and these studs provide it for an outlay well below that of a damaged block or crankshaft.