Gary Lewis Posted March 16, 2023 Author Share Posted March 16, 2023 Torque tests can be very inconclusive as thread condition, lubricant etc. can really change things. What you are trying to achieve is a desired clamping force or the point at which the bolt breaks. In the case of seat bolts that are generally loaded in shear, a less ductile grade is desirable. Ford put the seats in our trucks in with the front fasteners on a 45° angle where the rear ones are vertical. In a normal collision, the seat belts are going to take most if not all of the load, but a heavy unrestrained item behind a seat. As for breaking bolts and torque vs stress on them. In a test I performed for our QID (nuclear inspectors) I used a device called a Skidmore-Whihelm bolt tension indicator which is a hydraulic load cell that the bolt is inserted through and torqued. Lubrication is an eye opener, I was testing 5/8-11 gr 5 bolts, the specified lubricant is Neolube, graphite in isopropyl alcohol. Procedure is apply a coat to both parts, allow to dry fully, then repeat. The question was raised "what if it isn't dry?", at roughly 1/2 the specified torque, the bolts would just stretch apart with almost no effort. Dry, it is a so-so lubricant (works real well on Cub Scout Pinewood Derby cars), wet, it is slippery as goose poop. Jeff - That was my theory - the OD of the insert is like a larger bolt so will have more holding power. Bill - I thought you might have some input given your experience. So it might be that some of the inserts were either lubed or smoother? Or the surface of the aluminum was "better"? I would think that the bolt would twist off due to torque at the same ft-lb regardless of insert if all else was equal. Link to comment Share on other sites More sharing options...
Rusty_S85 Posted March 16, 2023 Share Posted March 16, 2023 Very true. And from what I've read the inserts provide more strength than normal threads. Perhaps that's because the inserts have a larger external thread in the base metal, which provides more strength. They do, its the insert being a stronger metal and the fact that your supposed to locktite the insert in place which I have never done on blind holes as when you bottom them out and break the tang off there is no way it is coming unthreaded. I used one on my 351W I had a bolt for the water pump break off in the block I drilled it out went with a helicoil in the OE size and put a insert. Link to comment Share on other sites More sharing options...
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