Reinforced ARP cylinder head studs FORD Pinto 2.3 OHC Lima

The engines concerned

Ford's 2.3-litre Pinto, known as the OHC Lima, is a 2,301 cc in-line four-cylinder (96.04 mm bore, 79.4 mm stroke) with eight valves and an overhead camshaft. Built from 1974 to 1997, it powered mainly Fords sold in North America: Mustang, Fairmont, Granada, LTD, Ranger, Aerostar and Courier.

As standard, the cylinder head of the OHC Lima is secured by cylinder head bolts, which the ARP studs replace.

Reinforced ARP cylinder head studs

The job of the head fasteners is to keep the cylinder head locked to the block despite the pressure inside the combustion chambers. They keep the gasket compressed; as soon as their clamping force drops, leaks appear between head and block.

This engine takes two ARP kits, the 151-4202 and the 151-4702, both in 8740 and 12 mm in diameter. According to the instruction sheets, the studs are screwed into the block by hand before the head is fitted, then the nuts are tightened in three equal passes, once the threads, washers and nuts have been lubricated with ARP Ultra-Torque. 8740 is a chrome-molybdenum steel, rated by ARP at 200,000 psi tensile strength. As a reference point, an engine's standard fasteners mostly belong to property classes 10.9 and 12.9, with a minimum tensile strength between 150,800 and 176,900 psi. In M12, the 8740 studs hold up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

For both kits: no torque is applied to the studs as they go into the block: they are screwed in by hand. The instruction sheet leaves the option of thread locker to mount them permanently, provided tightening is done before the product hardens.

According to the sheets, ARP thread sealer goes on the block-side threads when the studs open into the water jacket.

Final tightening is done in three successive stages, following the manufacturer's tightening sequence; these torque figures only hold with ARP assembly lubricant on the threads and under the nuts.

The instruction sheet also calls for ARP lubricant on the washers.

This torque value comes from ARP instruction sheets 151-4202 and 151-4702; the official sheet in force prevails for the whole procedure, including the manufacturer's tightening order. Read the ARP 151-4202 instruction sheet; Read the ARP 151-4702 instruction sheet

Technical guide

The stated tightening torques only make sense with ARP assembly grease, applied to the threads and under the nuts.

ARP undercut studs

The undercut version is recognisable by its reduced shank between the threads. According to ARP, this profile equalises stretch from one stud to the next and makes the clamping more consistent, while compensating for head gasket compression during installation: engine sealing benefits.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set itself the mission of eliminating engine failures caused by inadequate fasteners in competition. Its thousands of parts are designed and produced in California, in several material grades depending on the application.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Block threads	Stressed at every tightening	Spared by hand-tight fitting

When studs become necessary

Standard fasteners remain suitable as long as the engine keeps its original combustion pressure. They reach their limits in the following cases:

• Pinto 2.3 OHC Lima built for fast road, hill-climb or track use (turbo, raised compression ratio)
• Compression ratio raised for more power
• Reinforced MLS head gasket, which requires a high and even preload
• Cylinder head that has already lifted or gasket that has already leaked
• Racing or track use, with repeated heat-ups and frequent teardowns

Vehicle compatibility

Why is it the most cost-effective solution?

A standard OHC Lima is sized for factory output. As soon as a turbo build, a higher compression ratio or competition use pushes up combustion pressure, the head and its gasket are the first parts to suffer. ARP 8740 studs give the gasket a steadier clamping load; reopening an engine after a blown gasket costs far more than one of these kits.