Reinforced ARP main studs for NISSAN L24 L26 L28

The Nissan engines concerned

This kit is for Nissan and Datsun's L series: the L24 (2.4-litre), L26 (2.6-litre) and L28 (2.8-litre) in-line sixes that power the 240Z, 260Z, 280Z and 280ZX, as well as Skyline, Cedric, Laurel, Bluebird, Leopard and Patrol models. ARP covers them all with a single main stud part number, 202-5406.

From the factory, the main caps of these engines are held by the standard fasteners; the 10 mm studs in this kit replace them.

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 become indented and the bearing bore loses its shape.

These ARP 8740 steel studs, 10 mm, take the place of the original main cap fasteners. The block threads are cleaned and, if needed, run through with the ARP thread chaser, then the studs are screwed in by hand only. The caps, washers and nuts then go on, everything lubricated with the ARP Ultra-Torque, which the instructions prefer to engine oil. The final tightening of 81 Nm (60 ft-lb) is reached in three equal passes, in the manufacturer's sequence: 27, 54 then 81 Nm. Material: 8740, a chrome-moly steel that ARP specifies at 200,000 psi tensile strength. Factory-fitted fasteners usually belong to classes 10.9 and 12.9, with 150,800 to 176,900 psi minimum tensile strength. These 8740 studs in 10 mm take up to 1,400 hp on this six-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Fitting the studs: screwed into the block by hand, without a tightening tool. The ARP instruction sheet accepts a Loctite thread locker for a permanent installation, as long as tightening is finished before the product sets.

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

With stronger fasteners, the clamping force is no longer what it was originally: the size and roundness of the main bearing bores must be checked once installation is complete, and the bores line-honed if necessary with the final fasteners and lubricant.

Torque figures taken from the ARP 202-5406 instruction sheet, in the revision in force on the day of publication. In the event of any difference, the manufacturer's instruction sheet prevails. Read the ARP 202-5406 instruction sheet

Technical guide

The torque figures given only apply with ARP assembly grease, never with engine oil.

The ARP brand

Coming from the aerospace industry, Gary Holzapfel founded ARP (Automotive Racing Products) in the early 1970s to put an end to engine failures caused by weak fasteners in motorsport. The company designs and manufactures thousands of part numbers in California, in several material grades depending on the application.

Advantages over the original bolts

Criterion	Original main bolts	Reinforced ARP studs
Tightening effort	The bolt turns in the block thread	Only the nut turns, the stud stays still
Block threads	Worn a little more at every removal	Preserved as long as the stud stays in place
Fitting the caps	Cap held by hand while screwing	Cap guided by the studs

When studs become necessary

• 240Z, 260Z, 280Z or 280ZX built for road, track or historic rally
• Six-cylinder revved or boosted well beyond the original
• Engine out for a bottom end overhaul
• Play between caps and block, or worn block threads
• Forged crankshaft, rods or pistons to be fitted

Vehicle compatibility

Why is it the most cost-effective solution?

An L-series engine pushed on revs or boost, or simply entered in historic competition, asks a lot of its main caps. Securing them more firmly protects the crankshaft and the block's bearing seats, at a cost far below that of reconditioning the bottom end.

Consider the crankshaft main bearings

To complete the bottom end overhaul, consider the tri-metal crankshaft main bearings suited to these engines: