Reinforced ARP cylinder head studs Ford Volvo B5254 JZDA HUBA

The engines concerned

The 2.5-litre inline five-cylinder 20-valve engine, known at Volvo as the "white block" (B5254) and taken over by Ford as the Duratec 2.5T, powers the Focus II RS (JZDA, 305 hp), the Focus RS500 (HUBA, 350 hp) and the Focus II ST, as well as the Mondeo, S-MAX and Kuga with the 2.5 turbo engine. At Volvo it is found in the first-generation 850, S70, V70, C70 and XC70, then in the second-generation S40, V50, C30 and C70 in T5 form.

As original equipment, the cylinder head is held by bolts tightened to a torque and then through an angle, which stretch permanently as they are tightened and are not refitted.

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.

ARP offers two stud references for this engine: kit 251-4703, listed for Ford, and kit 219-4301, listed for Volvo. Their specifications are identical: ARP2000, M12 x 1.75 thread, 12-point nuts, same instruction-sheet torque.

According to both instruction sheets, the studs are first screwed into the block by hand; the cylinder head is fitted next, then the nuts and washers, lubricated with the ARP Ultra-Torque lubricant supplied, are tightened in three equal passes, in the manufacturer's tightening sequence. The kit supplied, whether it carries the Ford or the Volvo reference, is therefore fitted in the same way.

The ARP2000 range relies on an alloy steel developed by ARP: after heat treatment it reaches 220,000 psi tensile strength, and the threads are rolled afterwards. As standard bolts generally belong to classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum, ARP2000 exceeds them by 24 to 46 %.

In M12 x 1.75, the ARP2000 studs hold up to 900 hp on this five-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

The studs are fitted into the block by hand, without a torque wrench. For a permanent installation, the instruction sheet accepts thread locker, with tightening to be completed before it sets.

The instruction sheets ask you to clean all the block threads and, if necessary, to chase them with the ARP 912-0008 tap (M12 x 1.75).

ARP thread sealer is reserved for studs that open into the cooling circuit.

Thread locker may be used if the installation is to remain permanent.

The studs are fitted into the block by hand, without a torque wrench. For a permanent installation, the instruction sheet accepts thread locker, with tightening to be completed before it sets.

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.

According to the instruction sheet, ARP lubricant is also applied to the washers, as on the threads.

These torque figures are those of ARP instruction sheets 251-4703 and 219-4301; only the official sheets in force apply, as for the complete procedure and the tightening sequence. Read the ARP 251-4703 instruction sheet ; Read the ARP 219-4301 instruction sheet

Technical guide

To obtain the intended preload, ARP assembly grease must be present on the threads and under the nuts: the torque figures in the table are established with it.

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	ARP2000 studs
Block thread	Stressed at every tightening	Spared (studs screwed in by hand)

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:

• Power raised on a turbocharged five-cylinder (higher boost pressure, remapped engine management)
• 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?

The original head fasteners of the turbocharged five-cylinder are sized for stock power: as soon as boost pressure climbs, the head gasket and the fasteners are the first to suffer. ARP2000 studs bring a higher clamp load and keep the gasket pressed down; redoing a five-cylinder head, with gasket and labour, costs far more than the kit.