Reinforced ARP main studs for TRIUMPH TR7 2.0 SOHC

The Triumph 2.0 SOHC engine of the TR7

ARP lists this kit for the Triumph "2.0L SOHC TR7", a 1,998 cc four-cylinder fitted, according to the NGK catalogue, to the TR7 I Coupe (1975 to 1981) and the TR7 II (1979 to 1982). Part number 206-5404 is specific to this application.

The main caps of this 2.0 SOHC are held in standard form by the original fasteners; the 7/16 inch studs in the kit 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.

Kit 206-5404 comes with ARP 8740 steel studs, 7/16 inch and ARP Ultra-Torque lubricant. With the block threads clean, the studs go in by hand without a wrench, the caps are fitted, then the lubricated washers and nuts are added, never with engine oil. Tightening follows the manufacturer's sequence, in three equal passes, up to 108 Nm (80 ft-lb): 36, 72 then 108 Nm. Material: 8740, a chrome-moly steel that ARP specifies at 200,000 psi tensile strength, with threads rolled after heat treatment. Factory-fitted fasteners usually belong to classes 10.9 and 12.9, with 150,800 to 176,900 psi minimum tensile strength. The 8740 studs in 7/16 inch hold up to 1,200 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. Where a permanent installation is wanted, the ARP instruction sheet accepts a thread locker, provided the nuts are tightened before it sets.

The nuts are tightened following the order set by the manufacturer for the caps; every step is given in the ARP instruction sheet.

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 honed in line if necessary with the final fasteners and lubricant.

Torque figures taken from the ARP 206-5404 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 206-5404 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 fasteners	Reinforced ARP studs
Role in the assembly	Depends on the original fastener of the TR7	Stud fixed, nut tightened on the cap side
Thread wear	Depends on the original fastener of the TR7	Lightly stressed once the stud is in place
Cap centring	Depends on the original fastener of the TR7	Provided by the studs as the cap slides on

When studs become necessary

• TR7 with a 2.0 SOHC engine entered in historic rallying, on track or on the road
• Revs or boost raised compared with stock
• Complete bottom-end overhaul of the 2.0 SOHC
• Main cap seating to be reworked during a re-bore
• Forged crankshaft, rods and pistons to install in the TR7 block

Vehicle compatibility

Why is it the most cost-effective solution?

A TR7 2.0 SOHC revved or boosted hard loads its main bearings more. A few ARP studs cost little compared with a crankshaft or a block to replace.