Reinforced ARP bolts for OEM rods Rover K-Series 18K4F

The Rover K-Series 1.8 16v 18K4F engine concerned

This kit is for the Rover K-Series 1.8-litre 16-valve 18K4F engine, the naturally aspirated version fitted to the Rover 25, 45 and 218. ARP describes the application of this part number as “Rover K-Series” with an M8 thread.

On this four-cylinder, inertia loads on the rods climb with engine speed as soon as a build raises it, and the rod bolts are what hold them.

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.

The kit replaces the original bolt of each rod with an ARP2000 bolt of M8 diameter, with a 12-point head and no washer. ARP recommends tightening with stretch control; without a gauge, apply the torque given in the instruction sheet. 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. In ARP2000, these bolts are rated for 9,500 rpm at most (calculated estimate).

Technical specifications

Tightening torque and stretch

ARP recommends tightening by stretch; without a gauge, the torque is applied, for an accurate preload. The torque and stretch figures in the table apply with ARP lubricant.

Figures taken from the ARP 206-6007 instruction sheet, revision in force on the day of publication. Should any difference appear, the official instruction sheet takes precedence. Read the ARP 206-6007 instruction sheet

No thread locker is called for by the ARP instruction sheet for this kit: the bolts are fitted with ARP Ultra-Torque grease, on the threads and under the head.

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

Tightening is done with ARP assembly grease, on the threads and under the head: the torque and stretch figures in the table were established with it.

The ARP brand

ARP (Automotive Racing Products) came into being in 1968, when Gary Holzapfel, who came from the aerospace industry, decided to tackle the engine failures caused in motorsport by inadequate fasteners. Today the brand produces thousands of part numbers in California for the cylinder head, the main bearings and the connecting rods, in materials suited to each application, with manufacturing known for its consistency.

Vehicle compatibility

Why is it the most cost-effective solution?

A rod bolt that breaks on an 18K4F seldom destroys just one part: the rod, the piston and the block follow. Fitting ARP2000 bolts before pushing the engine costs a fraction of a bottom-end rebuild.