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  #1  
Old 12-13-2004, 02:39 PM
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Default Header Bolts

I'm going out on a limb here hoping to get some help in the forum since I failed at a few attempts at the hardware store trying to replace these missing header bolts. I would get some ARP bolts but I already tried that and they are too short. I have these 360 heads and was wondering if anyone knew if the header bolts are metric. I think i've been messing up by looking for standard. I have nothing to go by & I think they are 5/16ths but I could be wrong. I'm having a hard time finding what the pitch is since I rarely have to replace bolts like this. I think its 18 or a 20 pitch with fine thread. Also wondering if I should use a grade 8 bolt or a grade 5, I was shooting for grade 8 since its an exhaust bolt. I'm also trying to get these studs of the ends of the heads. This has been one eventful project, I litterally had no bolts whateover to rebuild this engine since the car was salvaged and this hardware store and some ARP should have this engine complete by this weekend. Anyhow, please help me with these header bolts if you have time.

Thanks,

Mike
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  #2  
Old 12-13-2004, 02:45 PM
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A local speed shop should have the correct bolts for the headers. MoPar can get the studs for the ends. (I like to run them too.) The sizes are standard.
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Old 12-14-2004, 12:19 AM
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The studs in the ends of the heads plug coolant passages, so goober them with silicone before installing them. The threads in the heads are 5/16 USS (5/16-18). All the header bolts I've used have been 3/4 inch long for headers with a 1/4 inch thick flange.

torch
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Old 12-14-2004, 12:49 PM
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Thank you. I'm glad I got this info before the weekend. I'll go get some bolts and try this again tonight
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Old 12-14-2004, 05:53 PM
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A little late but.......................... I run studs throughout. Studs offer a higher torque value over bolts. And yes, they are 5/16".
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Old 12-15-2004, 02:26 AM
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Why do studs offer higher torque value than bolts? I know they can offer better thread engagement and have some other advantages too, but what does better torque value mean, and how does the studs effect that?
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Old 12-15-2004, 04:24 AM
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Generally speaking, a stud is used in applications where it isn't going to be removed. One end of the stud has a tighter class of thread, and that end is screwed into the casting. It is a very tight fit, for a semi-permanent installation, and a stud driver or double nuts are required to screw it in.

The other end of the stud is a normal, free running fit that accepts a standard nut.

The advantage is, the nut holding on the manifold or whatever can be spun on and off repeatedly without wearing out the tapped hole in the casting. The stud material is a high grade steel with a high tensile strength.

Just for kicks and giggles, as a rule of thumb, a bolt or a stud must engage only 1 1/2 times the diameter to achieve maximum holding power. For example, a 1/2" bolt only needs to engage the threads in the hole to a depth of 3/4". Any more engagement is wasted threads, although many times this rule is not followed due to various materials and the availability of standard size fasteners. Designers strive (or should) to engineer components that can be assembled with standard length bolts. That holds down manufacturing costs.
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Old 12-15-2004, 05:14 AM
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At least the studs I have seen have usually coarse threads that go to the block, head or whatever, and fine threads for the nuts. Like you said, the thread engagement depth depends of the material and the forces. Using bigger thread engagement depth the forces are applied more evenly to the part and can prevent cracking in the long run compared to the one that is "just enough".
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Old 12-15-2004, 08:02 AM
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Biggrin

I was referring to the holding power of the stud, not the yield strength of the base material or the distribution of the force within. The 1 1/2 X depth formula is commonly used in manufacturing to determine how deep the threads in a hole must be to give the maximum bite in the material that will allow the full strength of the bolt to be realized. Any more thread depth is just belt and suspenders. The fastener will fail at 3D with the same force that it would fail at 1 1/2D.

Your point of 2 different thread pitches is well taken but omitted from my description because the question was about bolts VS studs and bolts are single pitch.
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Old 12-15-2004, 08:21 AM
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I got your point; with that (or actually even a little less) thread depth, the bolt or stud will break before the threads get hurt, if you understand what I mean.
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Old 12-15-2004, 10:10 AM
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Biggrin

We are in agreement.
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