Reinforced ARP cylinder head studs Nissan L20 L20A L20B L20E L20ET

The engine concerned

The Nissan L20 is a 2.0-litre inline four-cylinder offered as the L20A, L20B, L20E and L20ET (1,952 or 1,998 cc in the NGK catalogue), fitted to the Nissan 510, 610, 620, 710, 720, 810, Bluebird, 200SX, Laurel, Leopard and Skyline R30. ARP matches the four-cylinder L20 series to its 202-4201 stud kit, made of 8740 with 12-point nuts.

As built, the L20 cylinder head is tightened with the standard fasteners; the studs of ARP kit 202-4201 take their place, with their nuts.

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 kit 202-4201, in 8740, has a 10 mm diameter; the sheet does not give the pitch. It has the studs screwed in by hand only, the head fitted, then threads, nuts and washers lubricated with ARP Ultra-Torque before tightening to torque 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 10 mm, the 8740 studs hold up to 500 hp on this four-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.

All block threads are cleaned before fitting to ensure good engagement; the ARP thread chaser is used if needed.

When a stud ends in the water jacket, its threads are coated with ARP Thread Sealer; a permanent fit may take Loctite, once the fasteners are tightened.

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.

Values taken from ARP instruction sheet 202-4201, in the revision current on the date of publication. In the event of any discrepancy, the official instruction sheet prevails; it also details the full procedure and the tightening sequence. Read the ARP 202-4201 instruction sheet

Technical guide

All torque values on this page are given with ARP assembly grease on the threads and under the nuts; another lubricant would make them wrong.

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	Preserved: studs fitted 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:

• L20 pushed: output beyond stock
• 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 pushed L20, the standard fasteners soon reach their limit. 10 mm 8740 studs keep their preload at higher pressures, and their price weighs little against a cylinder head to be skimmed or a gasket to be replaced.