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Unread 05-15-2015, 12:07 PM   #1
mjlewis422
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Torque Specs

I watch a lot of videos on Youtube (especially when I'm doing something new) and noticed that most people don't use torque wrenches when changing/fixing parts.

How important is it to torque to spec or does it really matter?

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Unread 05-15-2015, 12:19 PM   #2
kg6mov
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Very.

I've yet to see a youtube video that isn't by a real mechanic that has good info in it.

If you under or over torque things you open yourself up to a host of problems. Over torque and you can damage the fastener, it may not fail immediately but it will probably fail. Under torque is the same, gaskets may not seal right or you may have enough movement for vibrations to work things loose, if the fastener goes into the oil or water channels it may leak and work itself loose, or the vibrations can damage the fastener.

Torque spec is of the utmost importance on some fasteners where it sets the preload on a bearing. Wheel hubs, diff bearings, etc are common failures when not torqued properly.

This is from the lugs being overtightened by the PO, they were installed with an impact gun instead of a torque wrench, the lugs disintegrated. It could have been much worse.
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Unread 05-15-2015, 12:22 PM   #3
zjosh93
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Holy can of worms Batman...

A lot of vocal opinions on this. Here's mine: buy a torque wrench or three and torque everything that has a torque spec. Never put anything together with impact tools.

Using a torque wrench takes almost no more time than cranking everything bubba tight. A torqued fastener is tight enough to hold, take shock loads, get hot/cool down forever without failing. Without being torqued you have no idea if the fastener is going to vibrate loose or fail because you pushed it into plastic deformation.

I clean every bolt and every hole before assembly and make sure to use oil/antisieze/assembly lube to ensure that the torque I'm reading is accurate. Most specs are for clean lightly oiled threads. If you can't thread it by hand you need to clean more.

I learned this the hard way.
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Unread 05-15-2015, 02:23 PM   #4
AVR2
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Some things I torque, others I don't. For example, suspension and steering parts - yes. Coolant reservoir mounting nuts - no.

There are also some fasteners that have a torque spec in the FSM, but I can't figure out how the hell you're supposed to get a torque wrench onto them. A good example would be the nuts that hold the fan to the water pump pulley on the 4.0L engine. There's barely enough room to get a standard 13mm wrench onto them, never mind a torque wrench.
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Unread 05-15-2015, 02:32 PM   #5
zjosh93
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Good point. A lot of fasteners I can't find a torque for so you do need to develop a feel for things.

I'd guess I don't generally torque fasteners less than 1/4" except for critical things and gaskets.

They do make crows foot ends for torque wrenches but you have to recalculate the reading because the length changes it. The beam length of the wrench that is. Extensions added between the wrench head and socket don't change torque.

Still, I just run the fan clutch nuts good and tight. I use thread locker in those cases as insurance.
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Unread 05-15-2015, 02:42 PM   #6
AVR2
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Quote:
Originally Posted by zjosh93 View Post
I clean every bolt and every hole before assembly and make sure to use oil/antisieze/assembly lube to ensure that the torque I'm reading is accurate. Most specs are for clean lightly oiled threads
FWIW, it says this at the start of the ZJ FSM...

"It is important to be aware that the torque values listed are based on clean and dry bolt threads. Reduce the torque value by 10 percent when the bolt threads are lubricated and by 20 percent if new"

The only time I've ever oiled bolts before torquing them was when I replaced my cylinder head.
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