Jim's technical tip by Jim Cannon
Torque is actually a measure of the twisting force on something, like a nut or a bolt. When you tighten a nut, you are actually stretching the bolt or stud that the nut is turning on. It is the stretch of the bolt or stud that provides the strong “clamping force” that holds everything together tightly. Think of the bolt or stud as a very powerful spring. You stretch it out when you tighten the nut and the stud or bolt “spring” keeps pulling it together. If a stud or a bolt is weak, due to age or corrosion, it will often break under the intense stress you are applying when you torque the nut.
Although Ford did not publish torque values “back in the day”,there are many values published today for nuts and bolts on a Model A. I recommend you follow them as a guide and use a torque wrench. Today's modern torque wrench “clicks” when you get to the desired torque. When it clicks, stop tightening. If you are going to insert a cotter pin into the nut after it is tight, keep turning the nut beyond the point where the wrench clicks, just until the cotter pin will slide in.
All published torque values, unless it clearly states otherwise, are for tightening a nut or bolt with clean, dry threads. This means the rust has been cleaned off of the bolt or stud threads (I use a wire brush) and they have been wiped dry. No oil or grease or anti-seize compounds should be applied to the threads that the nut will be turning on. (If you'd like to, a small drop of oil can be applied to the face of the head or other surface that a nut is tightening against, such as the boss on the top of a head, where the stud goes through the head.)
If you lubricate the threads on a stud or bolt, it will be too easy to turn the nut as you torque it. So when you stop at your target torque (say 55ft-lbs for a head nut) you will have stretched the bolt or stud more than 2 times as far as you would with the same torque with dry threads. This will be like over-torqueing the nut and can result in the stud or bolt breaking, the stud pulling out of the block, or the head or block cracking, due to too much stress on it. That will ruin your day! So clean the threads before you start, keep the threads dry, use a torque wrench, and stop pulling the instant the torque wrench clicks. You'll be glad you did.
