Another fine example. Bolt spacers for coil overs. Yes, you know they need to be a specific ID, you don't understand why ERW and too small of an OD leads to softer and thinner walls that collapse right at the bolt torque specification.
Knowledge does not equal understanding, yet again
- Thread starter mrblaine
- Start date
Brianj5600
TJ Expert
I don't understand why you have to tighten them to bolt torque specs? Double shear doesn't need all that clamping force.
OP
It surprises me how many mechanical engineers do not understand how bolts work. We will get an assembly that has a 20mm bolt in it and I bitch because it needs to be tightened to 300 plus foot lbs. Engineer that designed it says just tighten it up with loctite. I say how tight. He says till it feels right. Then I call him a fucking idiot and I get talked to by my boss.
For those that do not understand, bolts need to stretch to apply the proper clamp load they are 'designed' to hold. A good book to read is Carrol Smith's Engineer To Win. Talks about how stuff should be welded, bolted, and riveted together for race cars. It applies to jeeps too.
As a mechanical engineer I once wrote a program that you input the fastener diameter and what it was coated with be it zinc plated, anti-seize, 30w oil etc. then it would output the correct torque values based on our company established desired target clamping load.
OP
Oh I well understand but it is a mighty struggle to get that most basic of concepts across to folks and even then when they claim to get it, they still don't trust it.
x2 on Carrol Smith‘s books
http://www.carrollsmith.com/books/index.html
Engineer to Win, Prepare to Win, and Nuts Bolts Fasteners and Plumbing are all excellent reads for anyone that cares, needs, or should be concerned about how our vehicles should be put together and maintained.
Really guys, @mrblaine and others, cover the same issues concerning fasteners, torque etc. time and again. Thankfully they are willing, unlike other forums.
Read the books, maybe twice, then refer to them when you have a question.
Most of us will learn at least something
If the axle side track bar bolt needs to be tight enough to keep the track bar from knocking around, then so does a shock or coilover bolt.
Brianj5600
TJ Expert
I clearly stated that I don't understand. Why does Currie install instructions direct installers to use lower torque values than bolt torque specification.
https://www.rockjock4x4.com/CE-9801H
Does this mean that there are times when a larger diameter bolt is beneficial, but clamping force can be excessive? Does a single shear bolt like Currie uses for the frame side track bar lose shear strength as torque nears maximum recommended torque? It seems in that application that lower torque would be helpful since single shear adds tensile stress. I can't think of a reason why the rest of the bolts are not according to bolt torque specification unless it just isn't necessary.
Very true. It still does not explain why Currie does not recommend the accepted bolt torque specification for the smaller 10mm TB bolt. Currie recommends 50 and the charts 75.
It’s been a while but I believe the target was 80% of bolt yield. We did this for everything. Lock washers weren’t allowed anywhere on our equipment.
I know most of our service guys didn’t follow our torque specs but we still had them on all drawings.
OP
With the combination of your two sentences, you said you don't understand since double shear does not need the clamping force. That isn't true, at all.
I don't know or care why they use different torque values than typical unless they are also specifying the use of anti-seize with them.
Not enough info to make that determination but in general, no.
Single shear in that particular application does not add tensile stress. The tensile stress is present due to the stretch of the fastener which provides the clamping force to stabilize the joint and prevent the bolt from seeing shear stresses. The exact same amount of tensile stress is present in double shear applications of similar function since the purpose of the bolt in a slip critical application is to clamp the connection together and create enough friction between the faying surfaces so they do not move under the design load.
I suspect that whoever put the 75 number on a chart is mistaken. Depending on the condition, I'm seeing a low of 58 ft lbs up to 78 ft lbs for a 7/16-20 Grade 8. Low is lubricated with something like AS, high is dry which means plain, no plating, no thread locking compounds, etc. I would never hit the factory 10mm track bar bolt with 75 and expect good results. I would expect gradual to fast loosening and destabilization of the connection due to moving the fastener out of elastic deformation into plastic deformation and loss of clamping force. The reason I picked 7/16" is due to it being larger and requiring higher torque values. That 75 is a crazy number for a smaller bolt under most conditions. Plated or lubed is going to pretty much guarantee a bad connection.
OP
I use Fastenal's chart for a handy reference. They tend to run a bit more realistic and they use 75% of yield. Most of the other charts out there have some very odd flier numbers that are scary.
OP
Missed that the first time through. I see lots of companies use them, send them out with parts and there are very few places where they are appropriate and one would think that knowledge would be more common.
OP
I'm glad I'm not the only one with a pile of lock washers.
Just the other day the accessory drive brackets for my LS came with lock washers and I was wondering to myself if I'm the only one who exchanges them for regular washer.
While we're on the topic of fasteners, does anyone aside from ARP make stainless steel fasteners that would be a direct replacement for grade 8 or higher strength? ARP doesn't make every length as far as I can tell.
Torque values also change based on if the fastener is designed to be removed or not. I think for a permanent connection, the torque should be somewhere around 90 percent of yield. I got my degree 20 years ago though, and don't work much with critical fastener joints anymore.
Gotta be careful of those charts... They might not state the variables that go into their numbers.
Gotta be careful of those charts... They might not state the variables that go into their numbers.