Proper Engine Fasteners - Keep It Tight!

ARP tests rod bolts on special tightening and stretch testers before recommending a stretch length.

Whether you're installing head bolts or studs, the tapped hole must be clean to allow proper thread engagement and for accurate bolt torque readings. You'll want to clean the threads with a thread chaser (not a tap) and spray the hole with brake clean. Thread chasers only remove leftover debris from the threads and help clean each hole. Don't be tempted to use a tap instead, which removes metal from the block.

Bolts or studs installed into water jackets require sealant (per manufacturer specs) to keep the threads from allowing coolant to leak into or out of the engine. For these applications, be sure to use the manufacturer-recommended sealant.

Tightening head bolts using the torque-angle method is common with factory fasteners and OE applications. With this procedure, the amount of stretch in a given bolt is predicted by measuring the degrees of a turn from the point where the bottom side of the bolt head touches the mating surface until it reaches its torque value. The bolts used for this type of tightening technique are typically not reusable.

This reel of steel shows how a rod bolt starts life when it first arrives at the manufacturing facility.

At ARP, the threads are rolled after heat treating, to produce a beneficial compressive stress in the root of the thread. This counteracts the fluctuating tensile stresses that can lead to fatigue cracking. If heat treatment were to happen after rolling, the compressive stresses would be eliminated and it would reduce the fatigue resistance of the bolt. The bolts and studs are heat-treated for strength in this oven after they have been machined.

Studs provide improved clamping and improved gasket alignment and are especially beneficial for race applications. For street-performance applications, studs generally make it difficult to remove cylinder heads (around the master cylinder) and other items. For street applications, a good set of performance cylinder head bolts usually works well.

When installing new fasteners where the stretch method will not work, the fastener should be tightened and loosened several times before final torque. The amount of tightening and releasing depends on the type of thread lubricant used.

Mr. Gasket also offers a wide selection of fasteners for intake manifolds, heads, oil pans, valve covers, flywheels, and carburetors. Plus you have the option of various coatings, like black oxide, silver zinc, zinc dichromate, and chrome.

By far, one of the more trick items on the market is the Stage 8. Utilizing a patented clip, a locking retainer, and a GrooveLok bolt assembly, these specialized fasteners won't loosen up until you want them to, are available in both U.S. and metric sizes, and work great on headers and starters.