Reinforced ARP bolts for OEM rods MINI W10B16 W11B16

The MINI engines concerned

The W10 and W11 are the 1.6-litre engines with 16 valves of the first-generation MINI (R50, R52, R53), better known as the Tritec. The W10B16 is naturally aspirated (One 90 hp, Cooper 116 hp); the W11B16 is supercharged (Cooper S from 163 to 170 hp, John Cooper Works up to 218 hp).

The original connecting rod bolt of both engines carries the reference 11 24 1 485 407 (M8 x 45 mm): BMW prescribes tightening it to 20 Nm then 90 degrees, using new bolts, which makes it a single-use part.

Reinforced ARP bolts for connecting rods

At every engine revolution, the rod and piston assembly pulls on the rod cap, and only its bolts hold it against these inertia loads. The original ones are intended for stock power and for a single installation.

This kit replaces the original rod bolts with ARP 8740 bolts, tightened by measuring stretch, the method ARP recommends for this part, or failing that by torque. Material: 8740, a chrome-moly steel heat treated by ARP to 180,000 psi tensile strength, with threads rolled after heat treatment. Factory-fitted fasteners usually fall into classes 10.9 and 12.9, between 150,800 and 176,900 psi minimum. The engine speed allowed by the 8740 bolts goes up to 8,750 rpm (calculated estimate).

Technical specifications

Tightening torque and stretch

The method ARP recommends combines torque with a stretch check, for an accurate preload. The torque and stretch figures in the table apply with ARP lubricant.

Figures taken from the ARP 206-6008 instruction sheet, revision in force on the day of publication. Should any difference appear, the official instruction sheet takes precedence. Read the ARP 206-6008 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.

The ARP instructions for this kit require the big ends to be checked and resized once the fasteners are fitted: this job belongs to an equipped machine shop.

Measuring bolt stretch

Stretch measurement supplements torque tightening and gives the most accurate preload. It is done with the bolt in place: the gauge, fitted with a dial indicator, bears on both ends of the bolt and shows the stretch achieved, to be brought to the value in the table above. This avoids the variations caused by friction, which matters on a highly stressed engine.

Technical guide

All the torque and stretch values on this page assume ARP assembly grease on the threads and under the bolt head; engine oil does not replace it.

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

OEM reference (rod bolt): 11 24 1 485 407 (M8 x 45 mm)

Why is it the most cost-effective solution?

As original equipment, the rod bolt is tightened by torque then angle up to its yield point, which stretches it permanently. In 8740, the ARP bolts, reinforced and stronger, accept clearly higher engine speeds and inertia loads: less risk of a fastener-related failure, and therefore an engine repair far more expensive than the kit avoided.

Matching connecting rod bearings

To complete the bottom-end rebuild, we offer the connecting rod bearings intended for this engine.

Why not step up to forged connecting rods?

A forged rod, hot formed under high pressure from a steel such as 4340, gains density and homogeneity compared with a stock rod. Where the original rod, often made of sintered metal, is aimed first at cost, a 4340 forged rod shows about +19% yield strength, +8% tensile strength and +19 to +37% fatigue strength. It is the cornerstone of a solid high-power build. For your engine: