[jrabbit]

So torque-angle is not affected by the amount of friction created by the under-head bolt thread friction. Of course, if you change fasteners like converting to ARP bolts, then that torque angle spec cannot be used since the ARP’s fasteners are made from a much stronger steel. ARP supplies a specific torque to use instead while also specifying its own ARP Ultra-Torque thread lubricant. Using this lubricant creates a much more accurate and repeatable amount of friction. This creates a much more accurate clamp load. [links]

[pnnac]

The desired bolt pre-load is very important and is a value created by the bolt manufacturer. For any bolt, the combination of the strength of its material, diameter, thread, and length all play important roles in establishing the proper fastener stretch. This desired stretch is the amount of pre-load that the bolt is designed to accommodate and still return to its original length without compromising its strength. You can think of a bolt like a spring. As long as you don’t over-stretch the spring, it will always return to its original shape. If the bolt is over-torqued and stretched beyond its limit, this exceeds its yield strength which means it can no longer maintain the needed clamp load and must be replaced. more

[Hepatizon]

Another variable that directly affects normal torque values is accuracy of the torque wrench. It’s typical for a torque wrench to only be most accurate in one particular torque range. This is exactly how a torque wrench is calibrated. It’s easy to see how big problems could be created by a wrench that under-torques fasteners by perhaps 8 to 10 ft.-lbs. when the spec calls for 65 ft.-lbs. [links]

[wolfz0rz]

Jeff Smith: First and most importantly, let’s distinguish between what we’re talking about. Your first reference is to a torque-to-yield bolt. Your second reference is to torque-angle, which is not a bolt but a procedure used for tightening a fastener. So the first is a fastener, the second is a process. What’s confusing is that TTY fasteners are very often tightened using the torque-angle method. Let’s get into the details on torqueing fasteners and the critical differences involved with each. This is important stuff to know if you work on newer engines that use different torque procedures and unique fasteners.

[hubdawg]

One way to overcome the huge variable of friction when tightening fasteners like head bolts is to use a technique called torque angle. This differs from applying a simple torque. In torque angle, the first step is to establish an accurate starting point by applying a light torque to the bolt. With an LS engine inboard main cap bolt, for example, the first step is to torque each bolt to 15 ft.-lbs. At this low level, friction is not a major factor so the error induced by different lubes is minimal. here

[antz123]

Often, field operations personnel will use the chart included with a torque wrench to determine the amount of torque they should apply to a bolted joint in order to get the right amount of tension. However, these torque charts typically are based on the assumption that K=0.2 and experiments show that this assumption often may not be accurate. here

[rdmiller3]

For more information about how the nut factor relates to torque in a bolted joint, see our previous blog post: The Nut Factor Problem.

[doogso]

Directly measuring tension in a bolted joint traditionally has been difficult. The industry practice has been to measure the amount of torque required to tighten the bolt, and then attempt to relate that torque to tension.

[dwdollar]

where T is the torque measurement, K is the nut factor, F is the tension and D is the bolt diameter. With this equation, if you know K, F and D, you can multiply them to get the torque needed to tighten the bolt so that it has the right amount of tension. more

[cosurgi]

The nut factor, K, sums up the combined effects of many variables affecting the difficulty of tightening the bolt, such as friction. Some of these factors include the type and material of the bolt, washer and nut; the presence and type of any plating, coating or lubrication; the pitch or angle of the bolt threads; and corrosion and wear. more

[rodrick3nie]

* On many aluminum cylinder heads, hardened steel washers are required under the head bolts. The washers help distribute the clamping load and prevent galling when the bolt is tightened down.

[HZPyR8eVk]

Rust and corrosion in high mileage engines can cause cylinder head bolts to stick, so to help loosen up the threads prior to removing them, try this trick: here

[dorothymedney]

The metallurgy and heat treatment of TTY head bolts and regular head bolts is different, and you can sometimes tell one from the other by their appearance. A TTY bolt may have a narrower shank (so it can stretch more easily), and is often longer than a conventional head bolt. To be sure, refer to the vehicle manufacturer's service literature. Many parts stores can also look up your vehicle and tell you if it uses TTY head bolts or not. more

[kiba]

* Never reuse a torque-to-yield bolt. Because the bolts are designed to stretch once, stretching them a second time may stretch them beyond their yield point causing the bolt to break. They are one-time use bolts, so throw the old bolts away and buy new ones. [links]

[kedur31]

* TTY bolts are usually installed dry. Do not apply any oil, grease, assembly lube or sealer on the bolt threads. The reason why is because lubricants reduce friction when a bolt is tightened. This actually increases the torque load on the bolt, which may overload and stretch a TTY bolt too far, causing it to break. here

[Tilka]

A clean and minimal question and answer theme for WordPress and AnsPress. Theme can be used to create a professional Q&A community.

[Gordon]

Torque to yield is the method of tightening a fastener so that a high preload is achieved by tightening up the yield point of the fastener material. To do this consistently requires special equipment that monitors the tightening process. Basically, as the tightening is being completed the equipment monitors the torque verses angle of rotation of the fastener. When it deviates from a specified gradient by a certain amount the tool stops the tightening process. The deviation from a specified gradient indicates that the fastener material as yielded. The torque to yield method is sometimes called yield controlled tightening or joint controlled tightening. here

[jrabbit]

Torque to yield is the method of tightening a fastener so that a high preload is achieved by tightening up the yield point of the fastener material. To do this consistently requires special equipment that monitors the tightening process. Basically, as the tightening is being completed the equipment monitors the torque verses angle of rotation of the fastener. When it deviates from a specified gradient by a certain amount the tool stops the tightening process. The deviation from a specified gradient indicates that the fastener material as yielded.The torque to yield method is sometimes called yield controlled tightening or joint controlled tightening. more

[true]

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