Engine Studs: How Can You Achieve Proper Clamping Loads?

In too many cases, engine builders focus only on selecting the right components to build a specific engine. This means that they overlook the importance of determining clearances, intake flow, exhaust volume, flow, surface finishes, and precision assembly. The essential link that holds everything together is threaded fasteners. This section will cover a range of issues and concerns relating to the most vital components of any motor engine — studs/bolts and their handling.


Main Stubble

If possible, studs will be preferred to main-cap bolts in heavy-duty or performance applications. Because studs don’t twist during tightening, you can obtain more accurate torque values. Because the bolts do not twist during the tightening of the nuts, the studs only move in one direction. This provides better clamping force and more uniform clamping.  This is especially important with alloy blocks. The use of main cap studs reduces the time required to attach and align the cap. Because the cap clamps are performed during cap clamping, the main cap will not move as much.


Cylinder Head Studs

Again, as with main studs, it is preferable to use studs over bolts. This will vary depending upon the application. Studs may not be the most suitable option from a cylinder heads service perspective for street engine applications or where the heads are difficult or impossible of being removed with the engine in position. Bolts can be a better option for practical reasons, such as if a master cylinder, or any other component, prevents the cylinder heads from being removed and installed with the engine still mounted in the vehicle. However, studs are theoretically a better option if the circumstances permit.

Barra Head Studs make it easier to install cylinder heads. This is especially useful when the head will need to be removed frequently.

The use studs offer a much better torque loading function. As a bolt is being tightened, it causes both twisting (torsional loading) and stretching ("vertical, or an axial load"). This exposes the bolt to two forces simultaneously and causes frictional loads at thread engagement. The stud's vertical axis is the only one that stretches when the bolt is fastened to a Stud. The exposed end, or top, of the bolt, has "fine", threads. These threads enable precise and more accurate readings of torque when the nut (or torque/angle) is tightened to spec.


Installation Tips

For accurate torque, readings ensure that threads on the block as well as the studs remain clean. This is very important!

Because many applications have cylinder threaded openings that are open-to-water jackets, it's important to coat the lower block end of the Stud threads with a high-quality thread sealer. This step may be skipped if you're certain the holes won't leak water. It doesn't hurt. A locking compound can be applied to the threads to make the studs "permanent".

A locking compound must be applied immediately after stud installations so that the nuts can torque to the value required before the compound sets. To ensure that stud alignment is assured, the studs should be preloaded. Install the studs into your block using a finger-tight fit (or with a light preload as recommended). Tighten the studs without doubling-nutting. Tightening the nuts will not be able to clamp the load as long as thread engagement has occurred (the "course") side of the bolt is fully in the hole). If the studs in the block are too tight, they could splay and cause misalignment with the head gasket.