Originally Posted by nvestysly
I wouldn't hesitate to tighten - loosen - tighten your screws numerous times. I've done it on our hitch a dozen times. I did it again recently when we installed new axles on the trailer and the tongue height and hitch needed to be adjusted.
Take a look at the information on the table shown HERE
I presume you have grade 8 bolts, that's what I have and I would expect hitches to come with that hardware. The bolts on my hitch are 3/4" diameter (1-1/8 hex). The clamp load in the chart is just over 30,000 pounds!
The chart shows the torque for various friction factors of K=0.15, 0.18 and 0.20. The torque ranges from 282 - 376 LB-FT depending on the friction factor. Back when I was designing bolted joints I typically used K=0.20 as an approximation but the friction does vary depending on the material and plating. Regardless, the clamping load is intended to make the bolt act like a large rubber band - extending the bolt within it's yield curve as the nut is tightened and then returning to it's original length when the nut is loosened.
I wouldn't tighten and loosen indefinitely but a few times doesn't seem like a problem in my mind.
-If you remember Premier Fastener Corp. Of Euclid Ave. in Cleveland, they demonstrated, using a torque/tension tester
, that the nuts should be replaced every time
they were torqued to the usual 70% of the UTS
If not, and retorqued, you would loose about 20% of your tension using the same torque.
I was an agent for Premier, and using a t/tester, a 3/8" Supertanium fastener assy.; 60 lb. ft. of torque would give us about 10,500 lbs. of tension. This was with a dry, plated assy., f/f of .18.
By loosening and retightening the nuts, we would read about 8,500 tension. Quite a drop.
Me? I replace my OEM Grade 5 bolts/nuts with Grade 8 bolts, nuts and washers, and torque them to the hitch mfr's spec of Grade 5 bolts.
That way, I'm not working the nuts to full load, and can retorque them as required.
Unfortunately, Premier seems to be out of business, in Canada, and so Supertanium bolts [220 KSI] are no longer available.
I have used Aircraft MS-21250 bolts. [220 KSI] and DSC-97 nuts in the past, but now am retired, and no longer able to access them.