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Old 11-02-2002, 03:23 AM
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Wink 327 exhaust thread?

Could anyone tell me the specs for the inlet and exhaust manifold bolts on a 327 (and if they are common with all sbc's).
I could do with knowing what thread type they are (I presume UNC) and the diameter / length.
I'm new to the SBC having worked on the Buick 215s mainly. 215 has 3/8 unc x 1 1/4" exhaust and 3/8 unc x 1 1/2" inlet manifold bolts, are sbc the same?

Thanks in advance
Alastair

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Old 11-02-2002, 09:29 AM
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yes the threads are 3/8 unc, but the length will vary because of different style intake and exhaust manifolds, you just have to measure and try to get at least 1/2" thread engagement in the head.
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Old 11-02-2002, 10:03 AM
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Little known, less cared about fact; Did you know that for a bolt and nut of the same grade, the connection achieves full strenght with only 3 threads engaged? In other words less than 3 threads, the connection will fail in tension by the threads stripping out; 3 or more threads results in the bolt failing by pulling apart in tension while the threads are still in good shape. I didn't believe it either when I read it in my mechanical design text at college so I did an experiment in strength of materials lab and it is true. The crossover in failure mode occurs at EXACTLY 3 threads of engagement. Since cast iron is much weaker in tension and shear than the steel bolts, you must engage more threads than in a steel nut to prevent thread failuure, thus the need to have at least 1/2" engagement.
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Old 11-02-2002, 03:17 PM
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Also, good mechanical practice is to have at least the thickness of the bolt in thread depth. Most nuts equal the diameter of their respective bolts......Glenn K
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Old 11-02-2002, 03:53 PM
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Willys, we must have been reading the same books, way back when.
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Old 11-02-2002, 04:31 PM
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Shigley's mechanical Design?
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Old 11-02-2002, 05:40 PM
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I do remember the contents of the book and i do remember the school but i don't remember the title or author. but then there is a lot of the late 60's early 70's that i don't remember!
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Old 11-02-2002, 06:51 PM
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SO, since you two both seem to be so nuts, i mean into nuts, and bolts. do torque specs pretty much depend on the diameter of the bolt, regardless of number of threads, or sae or metric? (ps. dont know how many threads are in a given nut but i always made sure i have a bolt that at least is flush with the opposite side of the nut.) nice info guys
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Old 11-02-2002, 08:41 PM
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bulheimer, torque spec difer by the bolt material, thread, quality of fit, and lubricant used. check an a.r.p. catalog and just look at the difference moly lube makes over motor oil.
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