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Torque Wrench Extension

In certain situations, primarily due to access challenges, you may not be able to use your torque wrench when fitted with a socket wrench. In torquecritical applications such as cylinder heads or intake manifolds, you may run into cases where you simply cannot engage a fastener head using a conventional socket. In those situations, you can use a torque wrench extension that features a box-wrench.

By “extension,” we are not referring to a deepwell socket or socket extension that is in line with the torque wrench head. Instead, we’re referring to an offset extension that engages to the torque wrench drive, but effectively increases the length of the torque wrench. It features an open crows-foot or box wrench at the opposite end, and allows access perpendicular to the fastener. While such an extension allows easy access to the fastener, you need to understand that the torque wrench value setting must be adjusted in order to compensate for the increased leverage effect, since adding the wrench extension makes the tool longer. Because of this, if you set the wrench to the spec value, the added tool length will result in a slight over-tightening, beyond the torque wrench setting.

If you want to know where to set the torque wrench when using an adapter that alters the effective length of the wrench, you must calculate to compensate for the adapter. If the distance from the wrench drive to the center of the bolt makes the wrench longer, the final wrench setting must be adjusted to a lower value in order to compensate.

If the distance from the wrench drive to the bolt center makes the wrench shorter, the wrench must be set to a higher value.

The following is a method to make the calculation when the adapter makes the wrench longer:

E…………….Effective length of the extension (for example, using a 2-inch-ling extension)

L…………….Lever length of the torque wrench (from center of the wrench drive to the center of the adapter’s grip area)

TW…………Torque setting on the torque wrench

TE…………..Torque applied by the extension to the fastener

FORMULA: TW = L/L+E x TE

Let’s say that you want to torque a bolt to 30 ft-lbs., but you’re using a wrench extension. For this example, the length of the torque wrench is 12 inches from center of the handle to center of the drive. Let’s also say that the extension is aiming away from the wrench drive, making the distance from the center of the wrench drive to the center of the bolt 2 inches. This makes the torque wrench 2 inches longer. In this case, you would divide the length of the torque wrench (L…from the center of the handle to the center of the drive) by L+E, then multiply that ratio by the desired value.

In this example, where the torque wrench is 14 inches long and the extension is 2 inches long and we want to obtain 30ft-lb of torque value, the formula would be as follows:

(L) 14 divided by (L+E) 14+2 multiplied by (TE) 30 14 divided by 16 = 0.875

0.875 multiplied by (TE) 30 = 26.25. The new torque wrench setting should be 26.25 ft-lb.