Bolt torque discussion

nm9stheham said
And the finish surface on the threads makes large difference too, as well as any plating.

What most users do't realize with the ARP's is that they are not going up by 40-50% or in bolt tension/clamping force by going from, say, 85 to 130 ft lbs torque. Because the ARP lube is so much slicker than oil, the torquing friction is a lot lower and it takes lot more tension in the fastener on on the threads to get the torque friction up. The actual force achieved is somewhere in the 100% higher range over what the stock fastener torqued to 85 ft lbs with oil would achieve. That is a very rough number but you are in the ballpark with that %.

IIRC (and this is going back a while): The threads in the cast block are considerably stronger than the steel bolts/studs. Again, IIRC, this is due to the material properties of the cast iron.

Yes, surface finish affects the surface friction of the threads, which also will influence the torque on the bolt...

The coating/finish on the bolt also affects the surface friction... The surface friction is along the threads and the under side of the bolt head... This is what is 'dragging' as you try to turn/torque the bolt...

We used the standard phosphorus and oil on the connecting rod bolts in our factory... We used a special coating on the nuts that was more like a wax than an oil... It was dry to the touch but had a slight white 'haze' on the nut... If an engine was made and they found a defect in it and then tore it down and reused the parts, sometimes the connecting rod nuts would get dirty and need to be cleaned before we could reuse them... The cleaning would strip off the coating and they had to be re-coated... They tried to use different oils in place of the wax coating on the nuts, but it didn't work... The oil made the nuts much slicker and then they would fail in the torque multiple that torqued the connecting rod bolts... A 'torque multiple' is a machine with more than one spindle that can tighten more than one nut at a time... We tightened four nuts for two opposite cylinders at the same time with these machines... When we tried to re-oil the nuts our self in house, they would reject in the multiples more often... The repair loop for the connecting rods could only handle about 10 engines max... If we got a rash of rejects in a short amount of time, it would fill the repair station and then the next reject would stop the line as it could not get into the repair loop as the line was programmed not to let a reject pass by the repair loop...

So what we did then was send all the connecting rod nuts back to the supplier to be cleaned and re-coated with the wax so we could re-use them... We would also batch run the recycled nuts so we could keep track of them if they started to reject in the multiples too much... If they started rejecting too much, we would then remove them from the assembly line and use fresh boxes of brand new ones...

That is why I don't recommend using any extra lube on the nuts and bolts... The different oils can throw off the torque and clamp load... All fasteners at the factory are used as the supplier ships them in and all torque specs are made for those conditions... Only in the case like ARP where they supply the lube with the bolts and that is what they used to develop the torques with should you use lube on a bolt...