Reinforced ARP main studs for HONDA L15

The Honda engine concerned

This kit is meant for the L15A, Honda's 1.5-litre 16-valve four-cylinder found in the Jazz, Fit, City, Freed, Mobilio and even under the bonnet of the eighth-generation Civic. ARP lists it as Honda 1.5L (L15).

On this block, bolts hold the bearing caps when it leaves the factory; these studs replace them.

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.

The studs are screwed in by hand, the caps are fitted, then the nuts are tightened in three equal passes following the manufacturer's sequence. The washers go on with the nuts, after lubrication. Material: 8740, a chrome-moly steel that ARP specifies at 190,000 psi tensile strength. Factory-fitted fasteners usually belong to classes 10.9 and 12.9, with 150,800 to 176,900 psi minimum tensile strength. These 8740 studs in M10 x 1.25 take up to 800 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

The studs are screwed into the block by hand, with no torque. To leave the studs in place for good, ARP's instructions allow a Loctite thread locker.

The nuts are tightened in the sequence the manufacturer specifies for the main caps; the ARP instruction sheet for the kit describes the full procedure.

Stronger fasteners change the clamping force: the size and roundness of the main bearing bores are checked after installation, and the bores are line-honed if necessary, using the final fasteners and lubricant.

Final torque taken from the ARP 108-5401 instruction sheet, in the revision in force on the day of publication; intermediate passes calculated in equal parts. In the event of any difference, the manufacturer's instruction sheet prevails. Read the ARP 108-5401 instruction sheet

Technical guide

The torque figures given only apply with ARP assembly grease, never 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
Cap fitting	Bolts to be presented in the block at each fitting	Caps kept aligned by the studs
Block threads	Worn at every cap removal	Spared as long as the studs stay in place
Torque application	Torque passed to the bolt inside the block	Torque passed to the nut only

When studs become necessary

• Jazz, Fit or City 1.5 converted for track or competition
• L15A engine refreshed with forged parts
• Block opened up, bearing housings to be checked
• Power and revs raised above the standard engine

Vehicle compatibility

Why is it the most cost-effective solution?

An L15A built beyond standard asks more of its bearing caps than the original engine. ARP 8740 studs hold the crankshaft for a budget far more modest than reconditioning the block.