Deciphering bolt torque requirements

[WranglerX]

In simple terms the torque specification is for the single unit, the bolt..... NOT how it is used in the application.... As it is used in "application" is a engineering definition for whatever the "product" may be

 

[S854]

I contacted Kioti regarding the generic torque specs vs. specific torque specs (engine assembly, for example)...

Their recommendation was to use the wheel lug torque specs spelled out in the owners manual and then use the generic chart for all other "user serviceable" bolts/nuts on the tractor (user serviceable leaves out engine/transmission/injector pump etc.)...

 

[doneill127]

Be a little careful in using the charts based on bolt head or wrench size. There’s SAE, metric and there’s a JIS metric that has some different bolt head size for same bolt diameter. Here’s a post I put up a while ago.

Mahindra bolt torque chart

Was doing some maintenance on my tractor (about 150 hrs on it) and was going to check the torque on the bolts. It's a Max with FEL and Backhoe. Noticed that all of the bolts for the FEL and Backhoe are ISO metric or SAE and the manuals for these have recommended torque values and torque charts...

www.tractorbynet.com

 

[SmallChange]

Is there a standard relationship between bolt size and bolt head size?

I think there is. I know English sizes better so I'll use those as my example. 1/4" bolts take 7/16" wrenches, 5/16" bolts take 1/2" wrenches, 3/8" bolts take 9/16" wrenches, and so on. However, there are exceptions. In my experience fastener makers refer to "large pattern" and "small pattern" bolts if they take a larger or smaller wrench than usual. AFAIK these differences are never more than one step away.

One strategy you might use, given that you are just checking fasteners in place, is to derate a wrench size to the next sixteenth down (or next mm down), look up the typical thread size (you could look in the McMaster-Carr catalog which gives all the dimensions for bolts they sell), and test the fastener at that torque. This will test your bolt, but (probably) not at its full torque capability. And that's OK, I figure. Anything that is coming loose is probably going to take less torque than the next size down, so you will catch it. A bolt that is pretty tight, though not as tight as it's permitted to be, is still holding things together.