Reinforced ARP main studs for BMW MINI B48

The engine concerned

The B48B20 is BMW's 2.0-litre turbocharged inline four-cylinder petrol engine (1,998 cm³, 82 mm bore, 94.6 mm stroke), in production since 2014. It powers many BMW models, from the 1 Series to the 7 Series, the X3 to X6 and the Z4; under the B48A20 code, it also powers the MINI Cooper S and John Cooper Works. The B46B20, an engine of the same family, is also in the compatibility list.

Reinforced ARP 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.

This kit replaces the original main cap bolts with 10 ARP2000 studs, supplied with the nuts and washers the ARP instruction sheet lists. Each stud is screwed into the block by hand and the caps go on over them; washers and threads then receive assembly lubricant before the nuts are torqued in three passes. The caps are held with a higher and more consistent preload, without stressing the block threads.

These fasteners are made from ARP2000, an ARP-specific alloy steel that reaches 220,000 psi tensile strength after heat treatment; the threads are rolled afterwards. Compared with classes 10.9 and 12.9 of the original fasteners, from 150,800 to 176,900 psi minimum tensile strength, the margin ranges from 24 to 46%. These ARP2000 studs in M10 x 1.5 take up to 1,000 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

The studs are screwed into the block by hand, with no torque; the ARP instruction sheet for this kit does not call for a thread locker.

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 align honed if necessary with the final fasteners and lubricant.

Values taken from the ARP 201-5404 instruction sheet in force at the date of publication; the official instruction sheet prevails should any difference appear. Read the ARP 201-5404 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.

Advantages over the original bolts

Criterion	Original main bolts	ARP studs
Tightening	Bolt turned straight into the block	Three torque passes, gradual build-up
Block threads	Stressed by the rotating bolt at each tightening	Stud fitted by hand, no torque
Fitting the caps	Cap held by hand while threading	Cap guided by its two studs

When studs become necessary

• 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 engine, ARP2000 studs clamp the main caps harder than the original bolts and so limit the risk of bottom-end damage. The extra cost is small next to repairing a crankshaft and a block.