torque wrench question
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
A torque wrench that reads within 5% of actual value is plenty adequate for engine rebuild. Since most engines are put together without a torque wrench 
, the fact that you will be using one is a 'step ahead' already. 
, the fact that you will be using one is a 'step ahead' already.
Safety Car
Joined: May 2008
Posts: 3,755
Likes: 722
From: Lafayette Louisiana
Torque Wrench
My 2 cents worth:
-The factory did not use any better torque tolerance than we have available today. So the design considered that (I hope).
-I put my torque wrenchs in a vise in a horizontal position, tie a string to the centerline of the handle and put the square drive(1/2" to 3/8") in the vise.
-Measure from the centerline of the drive (1/2" or 3/8" ) to the centerline of the handle(and tied string) to get "length".
-Slowly add known weights to the string until you get the "click" or the number if a beam type.
-Use your calculator to multiply the "length" times the weight and thats your torque. Divide by 12 if you are looking for foot lbs assuming you measured the length in inches.
Good luck and I think it is best to use a torque wrench that has the desired reading in maybe the middle third or middle half of its range. Hope this helps.
-The factory did not use any better torque tolerance than we have available today. So the design considered that (I hope).
-I put my torque wrenchs in a vise in a horizontal position, tie a string to the centerline of the handle and put the square drive(1/2" to 3/8") in the vise.
-Measure from the centerline of the drive (1/2" or 3/8" ) to the centerline of the handle(and tied string) to get "length".
-Slowly add known weights to the string until you get the "click" or the number if a beam type.
-Use your calculator to multiply the "length" times the weight and thats your torque. Divide by 12 if you are looking for foot lbs assuming you measured the length in inches.
Good luck and I think it is best to use a torque wrench that has the desired reading in maybe the middle third or middle half of its range. Hope this helps.
Last edited by 20mercury; Sep 16, 2010 at 09:45 AM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Good advice there. The significant innaccuracy occurs on either end of the wrench's range. So if you have a 50-250 lb/ft wrench and you are working a fastener that calls for 50 lb/ft, it will not be accurate at the low end. If this is a critical fastener, like a rod bolt, it will not be properly stretched.
Thread Starter
Pro
Joined: Oct 2008
Posts: 645
Likes: 1
From: Hayward Wi
Good advice there. The significant innaccuracy occurs on either end of the wrench's range. So if you have a 50-250 lb/ft wrench and you are working a fastener that calls for 50 lb/ft, it will not be accurate at the low end. If this is a critical fastener, like a rod bolt, it will not be properly stretched.
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
One of my first jobs as a Marine many moons ago, after a year of school to be a calibration technician was to calibrate torque wrenches and pressure gauges. (Everyone started at the bottom until the next newbie checked in!)
Even when torque wrenches were dead on in the mid range, they were allowed to be out at the upper and lower 10% of the range of the wrench. In other words if your torque wrench goes from 50# to 150#, it's not recommended that you trust it below 55# or above 135#. Either use a smaller wrench or a larger one if you need to go there.
Good luck... GUSTO
Even when torque wrenches were dead on in the mid range, they were allowed to be out at the upper and lower 10% of the range of the wrench. In other words if your torque wrench goes from 50# to 150#, it's not recommended that you trust it below 55# or above 135#. Either use a smaller wrench or a larger one if you need to go there.
Good luck... GUSTO
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Most torque wrenches have a tolerance that is a percentage of the "full-scale" reading...(ie, 2% tol. on a 100ft-lb wrench is 2ft-lbs, regardless of what torque you are applying).
For a home garage, the best type wrench to use is the "beam" type; it has a solid metal arm and a pointer that is attached to the handle. As the beam deflects (with higher load), the fixed position pointer is used to read the value on the scale. The beam type is best, because it never changes calibration, unless you drop/damage it or overtorque it to the point the beam is permanently altered. "Click" type wrenches are about the worst to use, because folks don't know how to use them properly and their calibration is affected by internal cleanliness and corrosion of parts. Digital type wrenches are "cute", but worthless, IMO.
For a home garage, the best type wrench to use is the "beam" type; it has a solid metal arm and a pointer that is attached to the handle. As the beam deflects (with higher load), the fixed position pointer is used to read the value on the scale. The beam type is best, because it never changes calibration, unless you drop/damage it or overtorque it to the point the beam is permanently altered. "Click" type wrenches are about the worst to use, because folks don't know how to use them properly and their calibration is affected by internal cleanliness and corrosion of parts. Digital type wrenches are "cute", but worthless, IMO.
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Le Mans Master
Joined: Dec 2006
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From: Oquirrh Mountains
St. Jude Donor '09
Now you have two variables. Is the strain on the beam of the torque wrench really within manufacturers tolerances and was it read within x%. I doubt you can even read one of these within 5%. The only application they are really any better for is breakaway torque for bearing preload. Otherwise, stay with a clicker style wrence.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Having worked two years in the calibration laboratory for GM early in my [40 year] career, I know a thing or two about torque wrenches (and about every other gaging system known to mankind). Click wrenches are the worst reading gages for 'repeatability' and 'accuracy' because they are so dependent on the "feel" of the user for when to release them after the 'click'. Regardless of the last poster's dislike of them, beam types are the best wrenches to get...unless you have an appropriate method to calibrate them at your disposal.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 39
From: Fremont CA
I use my Snap-on Tech Wrench digital torque wrench on motor builds. I don't own very many Snap-on tools but, the driver can always check it on his in truck calibration bench when I come around. I also have "beam" type torque wrenches for motor/differential disassembly, to better check conditions of my work after the fact (an inch pound beam wrnech for differential/steering gearbox work.)
I wouldn't assemble anything I "loved" with a Harbor Freight torque wrench, I have one to check my lugnuts with at the autocross races, it cost about $14 and if I lose or drop it, I won't cry
I wouldn't assemble anything I "loved" with a Harbor Freight torque wrench, I have one to check my lugnuts with at the autocross races, it cost about $14 and if I lose or drop it, I won't cry
Last edited by Solid LT1; Sep 18, 2010 at 12:36 AM.
Le Mans Master
Joined: Dec 2006
Posts: 5,557
Likes: 9
From: Oquirrh Mountains
St. Jude Donor '09
Having worked two years in the calibration laboratory for GM early in my [40 year] career, I know a thing or two about torque wrenches (and about every other gaging system known to mankind). Click wrenches are the worst reading gages for 'repeatability' and 'accuracy' because they are so dependent on the "feel" of the user for when to release them after the 'click'. Regardless of the last poster's dislike of them, beam types are the best wrenches to get...unless you have an appropriate method to calibrate them at your disposal.
