Quote:
Originally Posted by S-Class Guru
Frank, a short flange portion under the head is 11.8 mm thick, then it necks down to 10.75 mm - this portion is 20 mm long. Then the threaded section is 11.8 MM, measured with a caliper - 41 threads at 1.75 mm pitch. The bolt bites about 12 threads into the block.
So, I can assume that the inner thickness of the threaded section is about as thick as the smooth necked-down section above, meaning that both the necked-down section and the first 30 threads above the block are involved in the stretching???, about 70 mm worth.
The entire bolt length under the head is 102 mm, with an allowed reusable length of 105.4!!!!!
Oh, 50 miles of highway today, not a hint of a leak!!!!!!!!
DG
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Quote:
Originally Posted by S-Class Guru
Frank, forgot about the gasket. been 5 years since I put the current one in, but it's a typical Victor Reinz composite with metal fire rings and a little molded line around the water jackets and bolt holes. No idea on the new or compressed thickness. But a typical gasket of that type would maybe be around .050 -.060 new and maybe compress .010-.015------ just guessing from previous forgotten Chevy adventures.
If you come up with a ballpark number on the strength/stretch characteristics of the bolt, please let me know - of course, I'm all in now.
I found the same bolt looseness on a JY head I bought a few yeas back.
Does this mean we all should have been going against all known convention and retorquing our heads periodically for the last 30 years? Or will my bolts all snap next week? Stay tuned, I'll keep my towing insurance current!
Driving over to ft Worth tomorrow - wish me luck.
Cheers,
DG
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S-C G:
Using the above information for the length of the deformable section of the bolt, the compression of the gasket, and the thread lead vs. degrees of rotation, a somewhat quick & greasy calculation suggests a stress level in the bolt of ~200,000 psi. 200K is safely within an ultimate strength of 285-300K, but about 65% above the yield strength. As a consequence the bolt has undergone a permanent deformation/stretch, which is what you felt as a plateau of the torque required to continue rotation of the bolt. Hence the term, "Torque-To-Yield".