torque specs

eman2289

Noob..but not incompetent
Feb 23, 2007
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Jersey
Am i correct to say that I remember something about needing higher torque on the wrench if an extension is used?
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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Valley of the Sun
No, that is not correct...extensions do not affect the accuracy of a torque wrench, assuming it is properly calibrated to begin with.

(Where do you guys come up with this stuff...MHG thickness, extensions, etc ?!?)
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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Only reason I said that is it's amazing how misinfo gets started, usually based on a bad assumption. For example, I've been preaching the ARP torque specs for a long time now...no one seems to go to ARP's site to figure out WHY you don't want to over torque or what goes into the specs they publish. It's not like you would be reading a novel and they are very specific in their reasoning.
 

Nick M

Black Rifles Matter
Sep 9, 2005
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eman2289;927149 said:
Am i correct to say that I remember something about needing higher torque on the wrench if an extension is used?

Yes. Depends on the extension though. A longer extension between the socket and wrench will twist more, making you hit your value before bolt does.

An extension on the handle does not matter.
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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Nick M;927605 said:
Yes. Depends on the extension though. A longer extension between the socket and wrench will twist more, making you hit your value before bolt does.

An extension on the handle does not matter.


Actually Nick, it's the opposite:

Force X Distance = Torque

If you lengthen the handle (say with a metal tube), you'll have to calculate the correct torque value:

C = D(A/A+B)

A = length of torque wrench
B = length of adapter (metal tube)
C = torque wrench setting
D = desired torque at wrench head (socket)

The "twist" using a socket extension is negligible.
 

hunka13

nonlurker
Dec 3, 2007
56
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clackamas oregon
i see what hes saying about the extention between the socket and the wrench twisting and lessening the amount of torque but is it enough of a difference to matter maybe if your ext is cheap quality versus snap-on how would you tell
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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This is an old wives tale, argued for years and disproved in many ways. Let's do a little physics.

One of the laws of physics governing force is: "For every action there is an equal but opposite reaction". Thus if you apply a rotary force to one end of a shaft (in this case an extension) it will take an equal but opposite force (resistance in this case) to prevent the shaft from turning, no more no less. If the force is less on the other end the shaft (fastener side), it will continue to spin in the direction to tighten. As resistance becomes more, then it builds until it is equal to the force applied, producing the "click" indicating proper torque has been reached.

If you use a shaft (extension) that is made of a material that will twist and then if you apply, say, 35 ft/lb of torque with a torque wrench then the wrench will read 35 ft/lb when it encounters that much resistance at the point of connection to the shaft (extension). Then if the shaft (extension) "twists" under this much force it will simply have wound-up until it reached 35 ft/lb of resistance on the fastener end. It's a simple laws of physics and there is no way around it. Whatever force you put into one end of that extension is how much resistance it is going to take to stop it from turning at the other end...if you apply a turning force to one end of a shaft then it will turn until the resistance on the other end is EXACTLY equal, no more no less. Saying that 400 ft/lbs of torque applied to one end of a 4 ft extension will only amount to 75 lbs on the other end defies Newtonian physics.

If you allow an extension to tilt even slightly then you are dealing with the lever effect and that would affect the reading so it is important to keep an extension centered over the fastener. Impact extensions deal with impulse force and is an entirely different matter. If you put a crows foot at the end of an extension, it will change the torque applied due to lever effect as well and, like I said, putting a pipe over the handle of the wrench will change the torque.
 

Nalleywhacker

Formerly gnarkill87
Oct 2, 2006
643
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chattanooga,TN
iam getting ready to put my head on tomarrow so let me get this strait. (iam using an hks mhg and arp head bolts) put the moly on the bolts and torque to 80ftlbs.