Rod Bolt Question?

General engine tech -- Drag Racing to Circle Track

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modok
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Re: Rod Bolt Question?

Post by modok »

gruntguru wrote: Tue Jul 17, 2018 10:07 pm Better still is a nut with slightly coarser pitch than the bolt, such that bolt stretch and nut compression when tensioned result in constant stress along the entire contact surface. (I am not aware of this technique being in use anywhere.)
I did hear of that idea several years ago, here or some other source. it sounds rational.
I believe the reason that isn't needed, or rather, that it isn't a main consideration, is because the threads in question are not square acme threads, and what they are threaded into is also flexible, and in most cases the bolt/stud is much harder and/or less flexible material than what it is threaded into.
if you turn things around, and use square thread forms or odd material combinations, it may become a thing.
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Re: Rod Bolt Question?

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If the nut is nearly or as hard as the bolt, a high stress concentration occurs at the first thread, which can lead to failure. A softer nut, correctly tightened, yields enough to distribute the load over a number of threads, ironically making for a stronger joint.
More than you'll need to know here: (p. 6/7 applies) https://www.fastenal.com/content/feds/p ... Design.pdf
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