Re: Bolt torque values

Posted by bc on March 12, 2021 at 09:26:50 from (24.255.129.137):

In Reply to: Bolt torque values posted by bc on March 12, 2021 at 07:24:34:

thanks. I found the torque tables on the side of classic plus plenty of other info is there. For the record, the shop did the rebuild of the engine itself, I'm just installing it back on the tractor plus all the extra stuff. I'd assume I can use grade 2 to bolt the gas tank down, the hood, and some of that stuff.

Now for a couple theory questions.

1. My review of the torque values both here and used by fastenal talks about the tensile strength/clamp down/proof load of a bolt. That I can understand but it appears that they are more worried about bolt thread stretch since grade 2 and grade 5 bolts of the same size have different torques. I also believe these torque values are based on using nuts of the same grade. To me that begs the question whether the torque value would be the same when threading into cast iron of the engine block, bell housing, and rear ends of a tractor as the tensile strength of cast iron would be different than the nut of each grade? I assume that is part of the reasoning behind using 25# for manifold bolts so you don't pull the threads out of the cast or break it off.

2. I would think that the strength of the steel used in grade 2, 5, and 8 would have the same clamp down values based on the same standard thread size and thread count would be same. For example, if you take two plates held together by a 1/2" bolt, stuck a jack between the plates, at some point the threads will stretch and the bolt will shear. Same deal if you hung something from a crane held by a bolt and keep adding weight it will finally break. Or say that you insert a hydraulic jack between a head and engine block, at some point the bolts will shear. Or if a crane tried to pick up a D10 bulldozer with a 1/4" chain, it will break.

So we are back to different torque values of different grade bolts based on their clamp down strength but it seems like it is a matter of getting the bolts tighten up enough so they don't come loose from vibration, etc. as opposed to a head or flywheel being pulled apart. So wouldn't a grade 2, 5, or 8 bolt with the same threads maintain the same hold down at the same torque when screwed into a cast iron block?

I may be off base here but I know there are some people here who know this stuff. And I know there are different safety factors here as well. Thanks.

Replies:

• Re: Bolt torque values Brendon-KS 11:09:02 03/12/21 (0)
• Re: Bolt torque values rustred 10:11:00 03/12/21 (0)

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