Paul Gale Appears as a Guest Courtesy of Our Friends at Zero Error Racing. Grade 8 hex head bolts are designed for use in tension applications. They provide a clamp up force (like using a c-clamp). The 1/4 inch diameter bolt used for SBD kingpins is rated for a maximum torque of 200 inch pounds (16.7 foot pounds).
Torque values are developed based upon the threads being absolutely dry – no lubricant. Any material (plating, liquid, or wax) applied to the bolt threads or nut threads, regardless of viscosity, will significantly alter the actual torque value achieved. A rough estimated of torque value change for the yellow zinc coated bolts used as SBD kingpins would be 50 percent. For example: To achieve the same clamp up force as dry threads with 100 inch pounds of torque, the lubricated threads torque value would be 50 inch pounds. Conversely: if a bolt/nut with lubricated threads is tightened to 100 inch pounds, you have actually tightened the kingpin to 150 inch pounds.
Caution: torque should always be applied slowly to the nut. 
Note: If torque is applied to the bolt head, the torque value should be increased 10 percent to achieve the desired value. For example: If you want to apply 100 inch pounds of torque to the kingpin. You would apply 100 inch pounds of torque to the nut or 110 inch pounds of torque to the bolt head.
Individual manufacturers using Grade 8 bolts in assemblies normally develop their own torque values based upon the specific application in which the bolt is being used. These manufacturer recommended torque valves range from 140 to 200 inch pounds. One manufacturer may specify 140 inch pounds while another manufacturer using the very same bolt will specify 180 inch pounds.
The strength of Grade 8 bolts can be increased by strain-hardening the bolt. A properly strain-hardened Grade 8 bolt can withstand 300 inch pounds of torque.
The proper torque for a SBD car kingpin depends upon several factors. The most important of which is driver control. The goal is to give the driver smooth positive control of the steering. If the driver turns the steering wheel, the front axle should immediately turn. Any left/right movement of the steering wheel should result in movement of the front axle.
A test to determine if a car has positive steering is to hold a front wheel with one hand and slowly turn the steering wheel with the other (the car shell should be removed for this test). If the steering wheel turns and you do not feel the front wheel move, the driver does not have positive steering.
Look closely at the steering cable during this test. If the steering wheel is turned and the front axle does not move, you will see the cable tighten and then go slack as the steering wheel is turned left and right.
A balance must be achieved between the front kingpin torque and steering cable tension. To improve the situation, I recommend taking apart the front kingpin assembly, removing any burrs or curled edges on the washers and then lubricating both sides of each washer and both sides of the axle. The lubrication used should be one that is intended for heavy loads such as LPS Magnum Lubricant with PTFE.
My recommendations for the front axle assembly:
1. Flat, smooth and lubricated washers
2. Smooth and lubricated axle
3. Steering cable adjusters made non-functional (adjust steering cable tension using the eyebolt on the front axle)
4. Steering cable tension set at approximately 25 pounds
5. Kingpin torque set at 200 inch pounds minimum to 300 inch pounds maximum
6. Zero cross-bind
My recommendations for the rear axle assembly:
1. Flat and smooth washers
2. Kingpin torque set at 200 inch pounds minimum to 300 inch pounds maximum
3. Zero cross-bind
Paul Gale
Florida Soap Box Derby
