Reinforced ARP main studs for NISSAN L20B

The Nissan L20B engine concerned

ARP lists this kit as "L20 Series 4-cylinder": it matches the L20B, Nissan's 2.0-litre in-line four, fitted from 1973 to 1987, according to the NGK catalogue, to the 200SX, 510, 610, 620, 710, 720, 810, Bluebird and Skyline R30. A single main stud part number, 202-5401, covers it.

From the factory, the main caps of these engines are held by the manufacturer's original fasteners; the 10 mm studs in this kit take their place.

Reinforced ARP studs for main bearings

Each main bearing takes a share of the loads the connecting rods pass on at every combustion. Pulled downwards, the main cap tends to slide on its parting line: over time the mating faces brinell and the bearing bore loses its shape.

Kit 202-5401 contains ARP 8740 steel studs, 10 mm. Once the block threads are cleaned, the studs are screwed in by hand only; the caps then go on, with the washers and nuts lubricated with ARP Ultra-Torque rather than engine oil. Tightening is done in three equal passes, in the manufacturer's recommended order, up to 81 Nm (60 ft-lb): 27, 54 then 81 Nm. 8740 is a chrome-moly steel heat treated by ARP to 200,000 psi tensile strength, with threads rolled after heat treatment. To put this figure in context, standard engine fasteners mostly belong to property classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum tensile strength. On this four-cylinder engine, the 8740 studs in 10 mm are rated for 1,000 hp at most (calculated estimate).

Technical specifications

Tightening torque

The studs are screwed into the block by hand, with no torque. If the assembly is to remain permanent, the ARP instruction sheet accepts a Loctite thread locker, with tightening carried through before the product cures.

Follow the cap tightening sequence recommended by the manufacturer when bringing the nuts up to torque; the kit's instruction sheet details each step.

Moving to reinforced fasteners changes the clamping force on the caps. After installation, the size and roundness of the bores are checked, then align honed if needed, always with the final fasteners and lubricant.

Values taken from the ARP 202-5401 instruction sheet in force at the date of publication; the official instruction sheet prevails should any difference appear. Read the ARP 202-5401 instruction sheet

Technical guide

Tightening is done with ARP assembly grease: the torque figures in the table were established with it, not with engine oil.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set out to prevent fastener-related engine failures in motorsport. Its thousands of part numbers are designed and manufactured in California, in materials chosen for each use.

Advantages over the original bolts

Criterion	Original main bolts	Reinforced ARP studs
Where the load goes	The bolt works in the block thread at every tightening	The stud stays fixed, the nut takes the load
Block threads	Marked by repeated screwing in and out	Kept intact while the stud stays in the block
Fitting the caps	Cap to be lined up by hand over the bolts	Cap guided by the studs already in place

When studs become necessary

• 510, 200SX, Bluebird or Skyline R30 with an L20B engine, built for road, track or historic rally
• L20B revved well beyond stock
• Bottom end out for a full overhaul
• Caps that no longer seat as they should, or block threads marked by repeated removals
• Forged parts to fit on the crankshaft, rods or pistons

Vehicle compatibility

Why is it the most cost-effective solution?

An L20 pushed on revs or boost loads its main caps harder. Securing them with ARP studs costs little compared with a crankshaft or a block to replace.