ARP reinforced crankshaft main studs for Toyota 2ZZ-GE

The engines concerned

The 2ZZ-GE is Toyota's 1.8-litre four-cylinder petrol engine, with twin overhead camshafts and sixteen valves. It powers the Toyota Celica (T23), Corolla (E12) and Matrix, the Lotus Elise and Exige and the Pontiac Vibe GT.

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 suffer brinelling and the bearing bore loses its shape.

The 10 mm ARP 8740 steel studs in this kit take the place of the original main cap bolts, together with their nuts and washers as the ARP instruction sheet lists them. They are screwed into the block by hand, then the caps are fitted; ARP assembly lubricant goes on the threads, nuts and washers before the nuts are torqued in three passes. The preload reached is higher and steadier than with the original bolts, without loading the block threads.

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. The 8740 studs in M10 hold up to 1,000 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Fitting the studs: screwed into the block by hand, without a tightening tool. Where a permanent installation is wanted, ARP accepts a thread locker of the blue Loctite type on the block-side thread, provided the nuts are tightened before it sets; none goes on the nuts or with ARP grease.

The nuts are tightened following the order set by the manufacturer for the caps; every step is given in the ARP instruction sheet.

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.

Torque figures taken from the ARP 203-5407 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 203-5407 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

ARP, short for Automotive Racing Products, was born in the early 1970s on the initiative of Gary Holzapfel, an engineer from the aerospace sector, in response to the engine failures caused in racing by inadequate fasteners. Today the brand produces thousands of part numbers in California, offered in several materials depending on the application.

Advantages over the original bolts

Criterion	Original main bolts	ARP studs
Preload build-up	Bolt turned in the block at every tightening	Nuts tightened in three passes, load spread out
Block threads	Exposed to the turning of the bolt	Stud fitted by hand, thread spared
Locating the caps	Cap held by hand while screwing in	Cap centred by the two studs

When studs become necessary

• Forced induction added, or boost pressure increased
• Higher maximum engine speed or longer crankshaft stroke
• Bottom end rebuild, where the original fasteners have to be replaced anyway
• Signs of cap walk or tired block threads
• Racing use, with repeated load cycles

Vehicle compatibility

Why is it the most cost-effective solution?

On a tuned 2ZZ-GE, ARP 8740 studs hold the main caps more firmly than the original bolts and lower the risk of bottom-end damage. Their cost stays modest next to replacing a crankshaft and a block.