The new triple clamps should grip the fork tubes as tightly as the original Triumph items. Triumph use galvanized 10 millimeter diameter by 1.25 millimeter pitch Allen bolts with a 27 Newton-meter dry tightening torque. What is the gripping force, I wonder?
I download a tightening torque chart from
www.rpmmech.com/docs/tightening_torque.pdf These charts are not uncommon in the mechanical engineering world. The metric unit chart for M10x1.25 bolts lists the clamp loads for various strength bolts. I plot them up as shown on the attached chart. A 13.5 kiloNewton (3030 pound) load corresponds to a 27 Newton-meter tightening torque.
It is during the 4th July weekend when I do this and in a patriotic moment I decide to use American size bolts in the new clamps. Three eighths inch diameter bolts with Unified National Fine (UNF) threads are similar to the metric size. I am not thinking clearly and I drill and tap the holes for 5/16 inch diameter bolts with Unified National Coarse (UNC) threads. A smaller size. Then I helicoil the threads. This makes it almost impossible to make the holes bigger for the 3/8 inch bolts. What do I do?
I download the tightening chart from RPM Mechanical for 5/16 UNC bolts and plot up the clamp loads for various torques as shown on the attachment. A 15.5 foot-pound tightening torque corresponds to a 3030 pound clamp load. These charts are for typical galvanized bolts with clean, dry, and rolled threads in good condition. I will use anti-seize, a lubricant. A rule-of thumb is to reduce the bolt torque when the threads are lubed. I use a typical reduction value of 75%. The tightening torque will be .75 x 15.5 = 11.6 foot-pounds. I will use 12 foot-pounds. It is easier to remember.
Tensile stresses in the bolts produces the clamp loads and the clamp loads make the gripping power. A Grade 2 5/16 NC bolt produces a 2162 pound clamp force, maximum, using the RPM Mechanical chart. It is too weak. A Grade 5 bolt produces 3341 pounds clamping force, maximum. This exceeds the 3030 pound clamp load that I need, so Grade 5 bolts will be used.
The helicoils are stainless steel and I like to use stainless bolts. Thread galling can be a problem with stainless steel bolts tightened greater than Grade 3 limits, based on my experience. The situation is worse when the threaded parts are similar stainless alloys, and the bolts and helicoils are. The anti-sieze will prevent this problem but I might forget to use it. I will use galvanized Grade 5 carbon steel bolts. This should work OK with no seizing, I hope.
The attachments are too big. I will shrink them and include them in the next reply.