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What size and grade are the bolts?
Add 2 to the number of tick marks on the bolt head and you'll get the grade. I bet they're Grade 8, meaning 6 tick marks.
Bolts are sized to be tightened to 75-80% of their yield strength. That's a standard design practice. So you won't for example, find a 1/2" bolt with specified torque 45 lb-ft. Well, you actually might, but absent the tightening specification, it's safe for the bolt to be torqued to 75-80% of its yield strength. There are charts all over the internet.

R.

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Thanks for the advice!

I've been looking on the net, and have found a few pages with some advice for roughly determining unknown torque specs such as marking the bolt orientation, backing it off and then torquing till the marks have lined up.

Im sure I just need to be in the ballpark really

Thanks again!

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Don't you have a torque wrench? Even a Harbor Freight one is better than guesswork.

Why can't you measure the bolt diameter?

Did you really want an answer to your question, or did you ask so you could say "my guess is close enough"?

R.

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I do have a torque wrench (the original post was asking for a factory torque spec after all ) and calipers to measure.

I am not an engineer, so I was just mentioning another method that I found on the Internet (it does involve using a torque wrench), but based on your response it sounds like it couldn't work here.

As you suggested, I will check the grade and measure the bolt. Then subtract a certain percentage of the yield strength. Hey, that still sounds like a ballpark number to me!

Thanks again, I do appreciate your help here!

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hi, there are 2 sizes of case bolts used. 3/8 bolts or 5/16 and they take different torque specs.

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Are you saying that there are 2 sizes in the same case, or a case will have one of those 2 sizes?

I pulled and measured a bolt last night,,, 3/8" grade 8. According to a bunch of engineering and bolt related websites, the torque for that bolt is anywhere from 22-35 ft-lbs lubed to 35-50 ft-lbs dry.

Should i just pick a number in that range and go with it?

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I like this chart from Portland Bolt:

http://www.portlandbolt.com/technicalinformation/bolt-torque-chart.html

To read up on the subject of bolted joints, Fastenal which is a major bolt manufacturer, has a technical manual you can download. Some of it is pretty heavy going, but it is accurate which is important.

For your 3/8" capscrews, which is what I think they are, I'd use the values 44 lb-ft for coarse threads and 47 lb-ft for fine threads. I'd torque them dry, because the values above are for dry threads. Properly torqued, they should not need any kind of threadlocker.

Torquing is a rather poor way of measuring clamping force, which is what one wants to set. But, measuring bolt length is pretty hard in many instances. There are theory-derived formulas for equating bolt torque and clamping force, but they are modified by empirically-derived factors for friction. This is why ARP is very specific about burnishing threads and using its proprietary lube on the threads. This can take most of the guesswork out.

If you understand this, you can see why auto manufacturers are migrating to torque-to-yield bolts in critical applications.

For your application, the values I gave are current design standard numbers.

R.

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Thanks!

I hate to keep dragging on a topic, but is there any reason why I shouldn't use the lubricated spec of 22 ft-lbs from the Portland Bolt link?

Thanks again, for sticking with me, and helping out!