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Kopycinski's Brain - Bolts, Nuts & Torque

Posted in How To on February 1, 2012
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As gearheads, we spend a lot of time wrenching on our rigs. It could be performing maintenance, fixing broken parts, or doing the fun process of upgrading our off-road vehicles. So, we spend a lot of time dealing with fasteners and the tools needed to remove and replace them. This month we’ll mention a few tips on working with nuts and bolts.

Inch-sized hardware should be chosen based on strength grade. Grades 2, 5, and 8 are common American standards. Grades 5 and 8 are appropriate for automotive use with Grade 8 being used in most cases. This photo shows from left to right: Grade 2 (unmarked), Grade 5 (three radial head marks), and Grade 8 (six radial marks). A common misconception is that it’s better to run Grade 5 bolts as opposed to Grade 8 bolts because a Grade 8 bolt is harder and more prone to snap and break where a Grade 5 will stretch more before breaking. However, the higher grade bolt is considerably stronger in both yield and tensile strength.

Today, you often need both inch- and metric-sized tools to work with various automotive nuts and bolts. Typical inch size hardware is most common from 7/16-inch to 7/8-inch and metric sizes are most common from 10mm to 19mm. Sometimes wrenches are close enough they can be swapped almost seamlessly. For instance a 9/16-inch is almost always interchangeable with a 14mm wrench, and a 3/4-inch with a 19mm wrench. Also, a 13mm can often be used in place of a 1/2-inch wrench. A few other wrenches are close and work in a pinch, but don’t fit ideally.

We prefer working with six-point sockets over 12-point versions most of the time. They fit bolt heads and nuts snugger and provide far better resistance to rounding off the hex when compared to a 12-point socket. A 12-point socket often fits looser and will usually slip over a damaged hex head easier, but there’s a greater chance of rounding a bolt head. The 12-point sockets do offer the advantage of engaging at more angles so can come in handy when ratchet swing is limited in tight places. However, fine-tooth ratchets can serve equally well in such a situation.

Critical assemblies—such as ring gears, cylinder heads, and numerous sealing assemblies—are typically specified with a fastener torque value and tightening sequence. Some torque specs are meant to apply to dry fasteners while others apply to fasteners that have been lubed. Ensure you understand the expected bolt preparation. Here are some common torque specs:

Chevy small-block head bolts 65 lb-ft
Chevy small-block piston rod nuts 45 lb-ft
Chevy small-block oil pan bolts 12 lb-ft
Dana 60 ring gear bolts 110 lb-ft
Dana 44 ring gear bolts 55 lb-ft

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