Torque Head Bolts

By: Wayne Mandeville

There are as many different ideas on repairs for Model A’s, but the following is essential in my opinion. After you have reached the final torque amount and have run the engine for a while, always re-torque using the following method.

Starting at nut #1: Loosen each nut 1/8 of a turn and then in one uninterrupted motion, torque the net back to the final torque amount. Do this one at a time in the correct torque sequence. DON’T loosen them all at once. Always re-torque the engine when it is cooled off. If you re-torque when the engine is warm you are doing absolutely nothing because you are simply torquing against expanded metal. It must be in a relaxed and in a cool state to properly re-torque.

 The purpose of backing off the nuts one at a time as stated above is simple. The torque reading includes the friction between the nut and the stud. When the nut takes a set it essentially gets “stuck” to the stud. If you torque the nuts to 65 lbs it could easily require 70 lbs or more to break loose the nut after it sticks. That even applies if the gasket had compressed and the true clamping pressure/torque is reduced---the reduced pressure/torque is why you re-torque. The result is a false reading if you simply set your torque wrench for 65 lbs and attempt to tighten further as the nut is “stuck”. In contrast if you back the nut off SLIGHTLY you are breaking the bond between the nut and the stud which allows for a proper read as you re-torque.

If you want to see the effect, notice that the nut will often turn much farther when backed off and re-torqued, sometimes as much as 1/2 of a round or so, with the same torque amount than it will if it is just re-torqued.

Consider the following two pieces of information about the necessity for re-torquing. First, I think the greatest question these days is “What the heck is the filler material between the copper sheet stocks in the head gasket?” In the bad old days it was asbestos,--highly stable, and after a second tightening, immovable. These days I do not know what it is. Some have said Kevlar and some had said other materials. One thing for sure though, it “squishes” and it takes a long time to stabilize. This is a very good reason to re-torque. Second, today’s head gasket is made for over bored engines and the head gasket has less sealing contact thereby making it easier to blow or fail.

Read this again in detail and really get the concept. If you disagree let’s have a good discussion at our meeting. The discussion/idea is to keep our Model A’s running. Please feel free to challenge so that we can always get the best results.

Wayne