After struggling with various combinations of extenders, including a crushed piece of pipe with a makeshift square key hole cut into it, I decided to try this method of extending my torque wrench so I could torque the head bolts on my shovelhead engine. I cut about two thirds of a bent twelve point 7/16" closed box wrench as shown, found a redundant 11/16" socket, and did some surgery on it. I used a 7/32" Zirconium drill bit to drill out a slot on each side of the socket so the wrench would slide through.
The result is a torque wrench extender that will easily handle the 65 foot pounds required to torque shovelhead head bolts! And this torque wrench from hell can easily get into all the tight spaces without requiring the removal of too many parts. You will probably need to grind down the wrench to enable it to fit around the bolt head. Be careful not to remove too much material, otherwise the wrench may not be able to take the torque.
After you have fitted the wrench handle to the drilled socket you will need to do a little math to determine the proper amount of torque to dial up for actual torque at the wrench end. You can calculate this by measuring the distance from the center of the torque wrench key to the center of the wrench end. The following picture shows a, the distance from the center of the wrench handle, b, the distance from the center of the wrench key to the center of the wrench end, and c, the sum of a and b.
The formula you use to calculate the reading on the torque wrench's
scale (at the handle in this Sears wrench) is:
For example, if you want to generate 65 foot pounds of torque at the wrench end, a is 13 inches and b is 2.5 inches, the setting for the torque wrench is (13 / (13 + 2.5))(65), or .839*65, or 54.516. Thus you would dial up 54.5 foot pounds on the torque wrench to get 65 foot pounds at the head bolt.
Keep in mind that the distance you place the handle of the wrench into your modified socket should be kept nearly the same as the distance when you measured it. Otherwise your torque readings will be in error.
Copyright © 2000, Nelson Johnson