Reinforced ARP cylinder head studs NISSAN A12 A14

The engines concerned

The Nissan A12 is a 1.2-litre in-line four-cylinder (1,171 cc, 73 mm bore, 70 mm stroke) and the A14 is its 1.4-litre version (1,397 cc, 76 mm bore). Both are 8-valve engines with overhead valves operated by pushrods, fitted to the Nissan and Datsun Sunny, Cherry, Pulsar, 210, 310, B210 and F10, as well as to the 1400 Bakkie pick-up.

On these engines the head is held as standard by bolts, which the ARP studs replace.

Reinforced ARP cylinder head studs

Cylinder head fasteners work constantly: they hold the head tight against the block, crush the gasket to the right value and hold back the push of the gases at every combustion. If they lose even a little tension, the gasket starts to leak.

ARP offers two stud kits for these engines, both in 8740, 10 mm in diameter and with 12-point nuts: the 202-4202 for the A12 and the 202-4203 for the A14. According to their instruction sheets, the studs are screwed into the block by hand before the head is fitted; washers and nuts, coated with ARP Ultra-Torque, are then tightened in three equal passes. Material of the fasteners: 8740, a chrome-molybdenum steel that ARP specifies at 200,000 psi tensile strength. Factory-fitted fasteners usually fall into classes 10.9 and 12.9, with 150,800 to 176,900 psi minimum tensile strength. In M10, the 8740 studs hold up to 500 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

For both kits: the studs are screwed into the block by hand, without torque. Their instruction sheet allows thread locker if they are to be fixed permanently, on the sole condition that tightening is finished before it sets.

According to the sheets, a sealant is applied to the block-side threads of only those studs that open into the water jacket.

Tightening to torque is done in three steps, in the order set by the engine manufacturer, with ARP lubricant applied to the threads and under the nuts, a condition for the table values to apply.

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

These torque values come from ARP instruction sheets 202-4202 and 202-4203; the official sheet in force prevails for the whole procedure, tightening order included. Read the ARP 202-4202 instruction sheet; Read the ARP 202-4203 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

ARP (Automotive Racing Products) was born in the early 1970s from the initiative of Gary Holzapfel, an engineer from the aerospace industry, determined to eliminate engine failures caused by weak fasteners in motorsport. The company designs and manufactures thousands of parts in California, in several material grades suited to each use.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Block threads	Stressed at every tightening	Preserved (studs screwed in by hand)

When studs become necessary

The original fasteners are sized for the engine as it leaves the factory. They need to be reinforced when:

• A12 or A14 built for competition (raised compression, modified carburation and ignition)
• The compression ratio rises as the build progresses
• The original gasket is replaced by a reinforced MLS gasket, which requires a high and uniform preload
• The engine has already suffered a lifted head or a gasket leak
• Competition use imposes severe heat cycles and regular head removals

Vehicle compatibility

Why is it the most cost-effective solution?

On a small overhead-valve four-cylinder, the original head fasteners are sized for standard output: once the engine is tuned, they and the gasket take the extra combustion pressure. ARP 8740 studs, screwed into the block by hand, pass a greater clamping load to the gasket; a cylinder head to redo, gasket and labour included, costs far more than this kit.

Consider a reinforced head gasket

Reinforced fasteners and the head gasket work together: the gasket must hold the same pressure as the fasteners. The matching gasket for this engine: