Reinforced ARP studs and bolts for main bearings Toyota 4A-GE

The engines concerned

The 4A-GE is Toyota's 1.6-litre (1587 cc) four-cylinder petrol engine, with twin overhead camshafts and sixteen valves, then twenty valves on the later versions, built from 1983 to 2002. It powers the Toyota Corolla (AE86, AE92, AE101, AE111), Sprinter Trueno, Celica, Carina, Corona Coupé and MR2 (AW11), as well as the Geo Prizm GSI. ARP also lists the 203-5403 stud kit for the 3S-FE, Toyota's 2.0-litre four-cylinder.

Reinforced ARP bolts and studs for main bearings

The bottom end rests on its main bearings: combustion after combustion, the loads coming from the connecting rods end up on them. Under this stress the main cap tries to move on its parting line, which eventually brinells the mating faces and distorts the bearing bore.

Two part numbers share this page: the 203-5403 stud kit and the 203-5001 bolt kit, both in 10 mm 8740 steel. The studs are screwed into the block by hand, then the caps, washers and nuts are fitted as the ARP instruction sheet lists them; the bolts are tightened straight into the block, with the washers the ARP sheet calls for, chamfered side towards the head. In both cases ARP assembly lubricant goes on the threads before torquing, in three passes. The preload reached is higher and steadier than with the original bolts.

ARP makes these fasteners in 8740, a chrome-moly steel; the stud instruction sheet gives 200,000 psi tensile strength after heat treatment; the threads are rolled once the treatment is complete. As a reference point, an engine's original fasteners generally fall into classes 10.9 and 12.9, whose minimum ranges from 150,800 to 176,900 psi. These 8740 studs in M10 take up to 1,000 hp on this four-cylinder engine (calculated estimate). The 8740 bolts in M10 x 1.25 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. The ARP instruction sheet allows a thread locker of the blue Loctite type on the block end for a permanent installation, provided the nuts are fully tightened before it sets; never on the nuts, never with ARP grease.

Each bolt holds the cap by tightening into the block thread; tightening is done to torque, in several stages, with ARP grease on the threads and under the head.

The 203-5001 bolt kit is M10 x 1.25; the ARP instruction sheet does not mention thread locker for this kit, so none is recommended here.

Follow the cap tightening sequence recommended by the manufacturer when bringing the nuts and bolts 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 align honed if necessary with the final fasteners and lubricant.

Values taken from the ARP 203-5403 and 203-5001 instruction sheets in force at the date of publication; the official instruction sheets prevail should any difference appear. Read the ARP 203-5403 instruction sheet ; Read the ARP 203-5001 instruction sheet

Technical guide

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

When to upgrade the main bearing fasteners

• Turbocharged or supercharged engine, or boost raised beyond stock
• Build that increases engine speed or stroke
• Bottom end overhaul
• Caps that have moved or marked block threads
• Track or rally use with repeated loads

Vehicle compatibility

Why is it the most cost-effective solution?

On a tuned 4A-GE, replacing the original main cap bolts with ARP 8740 studs or bolts holds the crankshaft bearings more firmly and lowers the risk of bottom-end damage. These kits cost little next to replacing a crankshaft and a block.