Reinforced ARP main studs for SUZUKI M16A

The Suzuki M16A engine

ARP lists this kit for Suzuki's 1.6-litre M16A: an inline four-cylinder 16-valve engine with double overhead camshafts and variable timing. According to the NGK catalogue, it powers the Swift III (125 hp, 2006 to 2015) and the Swift IV (136 to 142 hp, 2012 to 2017), but also the SX4, SX4 S-Cross, Vitara, Liana, Grand Vitara II and Jimny.

Originally, the main caps are held by Suzuki bolts with reference 12340-57K00 / 12340-57K02; the kit's studs, in 10 mm and 8 mm, 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 brinell and the bearing bore loses its shape.

The kit replaces the original main cap fasteners with ARP2000 studs in two diameters, 10 mm (M10 x 1.5) and 8 mm (M8 x 1.25). Block threads are first cleaned and inspected; the studs then go in by hand alone, and the caps are fitted over them. Threads and nuts receive the ARP lubricant supplied, preferred to engine oil. The nuts are first tightened by hand, then in three equal steps in the manufacturer's order: M10 at 95 Nm (70 ft-lb), that is 32, 63 and 95 Nm; M8 at 38 Nm (28 ft-lb), that is 13, 25 and 38 Nm. ARP2000 is an alloy steel developed by ARP and heat treated to 220,000 psi tensile strength, with threads rolled after heat treatment. Standard engine fasteners commonly belong to property classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum tensile strength: ARP2000 therefore sits 24 to 46% above that. The ARP2000 studs in M10 x 1.5 and M8 x 1.25 hold up to 1,100 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. For a permanent assembly, ARP's instructions permit a Loctite thread locker, provided full tightening is done before the product cures.

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 271-5201 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 271-5201 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	Reinforced ARP studs
Stress in the block	The block thread takes every bolt tightening	The block thread is spared, the load goes through the nut
Two diameters	One bolt per position, tightened one by one into the block	Studs of 10 mm and 8 mm, each with its own torque
Positioning	Each bolt is started blindly under the cap	The caps slide down over studs already in place

When studs become necessary

• M16A engine whose output is well above stock
• Building the M16A for the track, hill climbs or rally
• Engine stripped down to fit forged parts in the bottom end
• Main bearing bores to be redone with reinforced fasteners
• Engine regularly pushed to high revs

Vehicle compatibility

OEM reference: 12340-57K00 / 12340-57K02

Why is it the most cost-effective solution?

An M16A tuned beyond its standard output asks more of its main caps. Clamping them with reinforced fasteners costs little compared with a bottom end to rebuild after a crankshaft that has moved.