Reinforced ARP cylinder head studs Nissan KA24E

The Nissan engines concerned

The KA24E is Nissan's naturally aspirated 2.4-litre inline four-cylinder, with a single overhead camshaft and 12 valves (2,389 cc, 89 mm bore, 96 mm stroke). It powers the Nissan 240SX and 200SX (early S13), the Navara pick-up (D21, D22), the Pintara, the Serena and the Terrano II, among others. ARP offers a single kit for it, the 202-4307, in ARP2000 studs.

As original equipment, the KA24E cylinder head is tightened in several torque passes, with a complete loosening in between, then through an angle.

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.

The ARP 202-4307 kit combines ARP2000 studs in M10 x 1.5 with their 12-point nuts.

According to the instruction sheet, the studs are screwed into the block by hand before the cylinder head is fitted; the nuts are then tightened in three equal passes, up to 70 ft-lb.

Developed by ARP, ARP2000 alloy steel is heat treated to 220,000 psi tensile strength, and its threads are rolled once the treatment is done. Compared with the 10.9 and 12.9 classes of standard fasteners, between 150,800 and 176,900 psi minimum tensile strength, the gap reaches 24 to 46 %.

In M10 x 1.5, the ARP2000 studs hold up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

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.

The instruction sheet cites the ARP thread chaser 912-0003 (M10 x 1.5) to clean up the block threads if needed. If the studs open into a water jacket, it says to coat their block-side threads with ARP thread sealer.

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 washers also receive ARP lubricant, as stated in the instruction sheet.

Source of these values: ARP instruction sheet 202-4307, revision current at the time of publication. The official instruction sheet applies if any discrepancy appears; it covers the entire procedure and the tightening sequence. Read the ARP 202-4307 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
Tightening method	Several passes with an intermediate loosening, then an angle	Torque only, in three passes
Block threads	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:

• Engine moved to forced induction (turbo or added supercharger) or hard-tuned build
• 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 KA24E leaves the factory with cylinder head fasteners sized for its stock output. As soon as a build raises the pressure in the chambers, through boost or a higher compression ratio, the gasket's grip depends first on the clamp load. ARP2000 studs hold that load without turning the block threads at every tightening. The kit costs far less than a cylinder head to redo, gasket and labour included.