Reinforced ARP bolts for OEM rods TRIUMPH KE1L KE1H KE2L CR1H CF1

The Triumph GT6 2.0 litre and TR6 2.5 litre six-cylinder engines concerned

This kit is for the Triumph inline six-cylinder engines: the 2.0 litre of the GT6, built from 1966 to 1973 in three series, and the 2.5 litre of the TR6, built from 1969 to 1976.

This ARP kit takes the place of the original rod bolt on these six-cylinder engines, with ARP2000 cap screws that have no washer. ARP's documentation is silent on both the part number and the diameter of the bolt fitted originally.

Reinforced ARP bolts for connecting rods

At every revolution, the rod bolt takes the pull of the rod and piston assembly, which tries to force the cap away through inertia. As original equipment, it is sized for stock power and is replaced at every strip-down.

The ARP 206-6005 bolts, in ARP2000, are preferably tightened by stretch, the method ARP recommends; without a gauge, the instruction sheet gives a torque of 61 Nm. ARP2000 is an alloy steel developed by ARP and heat treated to 220,000 psi tensile strength; its threads are rolled after heat treatment. Standard engine fasteners commonly fall into classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum strength: ARP2000 sits 24 to 46% above that.

Technical specifications

Before fitting the bolts, ARP asks you to check the chamfer around the hole in each rod cap: without enough chamfer, the radius under the head will not seat.

Tightening torque and stretch

ARP recommends tightening to a measured stretch, which gives a more accurate preload than torque alone, given as a fallback. Torque and stretch figures assume ARP lubricant.

Figures taken from the ARP 206-6005 instruction sheet, revision in force on the day of publication. Should any difference appear, the official instruction sheet takes precedence. Read the ARP 206-6005 instruction sheet

The ARP instruction sheet does not require a thread locker for this kit; only ARP Ultra-Torque grease is applied, on the threads as well as under the bolt head.

According to the ARP instructions, the big ends must be checked and resized with the fasteners in place; plan a visit to a machine shop.

Measuring bolt stretch

Tightening to stretch means setting the preload on how much the bolt actually stretches, rather than on a torque affected by friction. With the bolt fitted, the dial gauge is placed on both its ends and the bolt is tightened until the stretch given in the table is read. It is the safest method on a highly tuned engine.

Technical guide

Torque and stretch figures are only valid with ARP assembly grease, applied to the threads and under the head.

The ARP brand

An engineer with an aerospace background, Gary Holzapfel launched ARP (Automotive Racing Products) in the early 1970s with one goal: to eliminate engine failures caused by weak fasteners in racing. ARP designs and manufactures thousands of part numbers in California, cylinder head, main and rod bolts, in several materials depending on the use, and has become known for the consistency of its manufacturing.

Vehicle compatibility

Why is it the most cost-effective solution?

A GT6 or TR6 six-cylinder that is made to turn harder asks a lot of its rod bolts, and the failure of a single one costs the rod, the block and often the crankshaft. An ARP2000 set is modest next to a complete rebuild.