Reinforced ARP cylinder head studs BMW M30B28 M30B30 M30B32 M30B35

The BMW engine concerned

The M30 is BMW's inline six-cylinder petrol engine with twelve valves, offered as a 2.8-litre (M30B28, 2,788 cm³, 86 mm bore, 80 mm stroke), 3.0-litre (M30B30, 2,986 cm³, 89 mm bore, 80 mm stroke), 3.2-litre (M30B32, 3,210 cm³, 89 mm bore, 86 mm stroke) and 3.5-litre (M30B35, 3,430 cm³, 92 mm bore, 86 mm stroke). It powers many BMWs, from the E9 coupé to the E32 7 Series, including the E12, E28 and E34 5 Series and the E24 6 Series.

As standard, the cylinder head is held by 156 mm M12 bolts (part number 11 12 0 621 144), which must be replaced, washed and oiled. They are tightened to 60 Nm, then to 80 Nm after a 20-minute wait; the engine is then warmed up for 25 minutes before a final 35° angle.

Reinforced ARP cylinder head studs

Cylinder head fasteners work constantly: they hold the head tight against the block, crush the gasket to the right value and hold back the push of the gases at every combustion. If they lose even a little tension, the gasket starts to leak.

The ARP 201-4602 kit brings together 14 studs in 8740 steel, 14 nuts (12-point) and 14 washers, in 12 mm diameter. According to the instruction sheet, the studs are first screwed into the block by hand; the head is then fitted and the nuts are tightened to torque. The block threads are spared and the preload exceeds that of the original bolt.

8740 is a chrome-molybdenum steel, rated by ARP at 190,000 psi tensile strength. As a reference point, an engine's standard fasteners mostly belong to property classes 10.9 and 12.9, with a minimum tensile strength between 150,800 and 176,900 psi.

On this six-cylinder engine, the limit of the 8740 studs in M12 lies at 900 hp (calculated estimate).

Technical specifications

Tightening torque

The studs are fitted into the block by hand, without a torque wrench. For a permanent installation, the instruction sheet accepts thread locker, with tightening to be completed before it sets.

When a stud enters a water passage in the block, the instruction sheet provides for its threads to be coated with ARP Thread Sealer.

Tightening to torque is done in three steps, in the order set by the engine manufacturer, with ARP lubricant applied to the threads and under the nuts, a condition for the table values to apply.

The instruction sheet also calls for ARP lubricant on the washers.

Values taken from ARP instruction sheet 201-4602, in the revision current on the date of publication. In the event of any discrepancy, the official instruction sheet prevails; it also details the full procedure and the tightening sequence. Read the ARP 201-4602 instruction sheet

Technical guide

The stated tightening torques only make sense with ARP assembly grease, applied to the threads and under the nuts.

The ARP brand

Gary Holzapfel, a former aerospace engineer, created ARP (Automotive Racing Products) in the early 1970s to tackle engine failures caused by insufficiently strong fasteners in racing. Today the brand develops and manufactures thousands of parts in California, available in several material grades as needed.

Advantages over the original bolts

Criterion	Original head bolts	8740 studs
Tightening	Torque then angle (60 Nm, 20 min wait, 80 Nm, 25 min warm, 35°)	Torque only, in three equal stages
Block threads	Stressed at every tightening	Preserved (studs fitted hand tight)

When studs become necessary

On an engine left standard, the original fasteners do their job. Switching to reinforced fasteners becomes worthwhile as soon as:

• Boost pressure exceeds the original value, or a turbo or supercharger is added
• The compression ratio is increased
• A reinforced MLS gasket is fitted, with its need for a high and even preload
• The head has already lifted or the gasket has already failed
• The engine is used in competition, with intense heat cycles and repeated teardowns

Vehicle compatibility

OEM reference: 11 12 0 621 144

Why is it the most cost-effective solution?

As standard, the head bolts are tightened to torque then angle and stretch permanently. Stronger, the ARP 8740 fasteners stand up to a much higher combustion pressure, forced induction included: they reduce the risk of gasket leaks or breakage, and therefore of a rebuild out of all proportion to the price of the kit.