AETC 2014: ARP’s Chris Brown And Fastener Strategies For Performance

The final presentation of the 2014 edition of the 2014 AETC event was a seminar from ARP‘s Chris Brown, whose presentation was entitled “Explaining Proper Fastener Strategy To Maximize Power And Durability”.

His demonstration covered basic fastener principles, but was greatly focused on two terms – torque and preload. Interestingly, as his presentation directly followed that of Cometic’s Mark Chollett, he discussed the idea of a fastener and how it acts as a spring – much like Chollett did regarding the MLS gasket technology.

“Of course, all materials have some elastic ability to them, but a bolt simply works by expanding the thread to create clamp load. The clamp load is created because you’re stretching the material. If the fastener is not tightened correctly, the preload is not going to be there, the stretch in the bolt is not going to be there, and you’re not going to have the clamp load,” says Brown.

As seen in the accompanying photo, the relationship between the stretch and the clamp load is linear and straight.

“In some cases, we have the ability to measure both ends of the bolt or stud. That really is the ultimate way to install it – to ensure the right amount of preload exists,” he says. The classic example of this relationship is in using a stretch gauge to measure connecting rod bolt stretch, rather than just measuring torque on the bolt after it’s fastened.

Brown discussed the challenges to building and testing fastener materials to work with all sorts of different loads, like cylinder loads, which see gas pressures, main cap loads, which are subject to combustion loads as the crank rotates and combustion forces the rod and piston assembly down, along with reciprocating loads like connecting rods – the highest stress point in the engine.

“At top dead center, the connecting rod’s big end goes oval-shaped, and there’s a significant bending load at the 3 and 9-o’clock positions. The fatigue that load presents is the issue, and that’s what determines the life of the connecting rod bolt,” says Brown.

He also covered the differences in friction coefficient between varying types of fastener assembly lubricants from oil to ARP’s Ultra Torque lubricant. As shown, the advantage to the Ultra Torque is that it’s extremely consistent from cycle to cycle, where other lubricants vary wildly.