Reinforced ARP main studs for FORD Pinto Lima

The Ford engine concerned

This kit fits Ford's 2.3-litre four-cylinder known as the OHC Lima or Pinto 2.3: 2,301 cc, eight valves, overhead camshaft, built from 1974 to 1997. It is found mostly in North American Fords and Mercurys (Mustang, Ranger, Fairmont, Thunderbird, Merkur XR4Ti) and in the Pinto.

On this engine the main caps are secured by Ford's original fasteners; the 12 mm studs in this kit are fitted in their place.

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 become indented and the bearing bore loses its shape.

The ARP 8740 steel studs, 12 mm, in this kit replace the original main cap fasteners of the Pinto 2.3. After checking the block threads, they are screwed in hand-tight only. The caps, washers and nuts then go on, and studs, nuts and washers are lubricated with ARP Ultra-Torque rather than engine oil, which the instructions advise against. Tightening is done in three equal passes, following the manufacturer's sequence, up to 122 Nm (90 ft-lb): 40, 81 then 122 Nm. 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. The 8740 studs in 12 mm hold up to 1,200 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

The studs are screwed into the block by hand, with no torque. If the assembly is to remain permanent, the ARP instruction sheet accepts a Loctite thread locker, with tightening carried through before the product cures.

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

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 the bores line-honed if necessary with the final fasteners and lubricant.

The torque figures above come from the ARP 151-5402 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 151-5402 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	Reinforced ARP studs
Tightening	Rotational effort passes into the block thread	Only the nut turns, block threads stay at rest
Successive removals	Block threads worn a little by each screwing	Stud stays in place, block threads preserved
Fitting the caps	Cap has to be held while screwing	Cap located by the studs

When studs become necessary

• 2.3 Lima built for drag, track or historic rally
• Boost or revs well above the original
• Bottom end opened for a full rebuild
• Main caps that move or tired block threads
• Fitting a forged crankshaft, rods or pistons

Vehicle compatibility

Why is it the most cost-effective solution?

A 2.3 Lima pushed with boost or revs, whether in a drag car, on the track or in historic rally, loads the main caps far beyond what the original design allowed for. A more reliable clamp on the caps protects the crankshaft and the block, and these studs provide it for far less than the cost of a damaged block or crankshaft.