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MG MGA - Final Bit on Torque Wrenches

Just thought I'd throw my final thoughts on the torque wrench issues we discussed in the engine Rebuild Checklist thread.

My final conclusion was to buy a new torque wrench. Not because I doubted it's calibration. I do wish there were a quick and easy empirical method to calibrate torque wrenches though... The fact of the matter was that after hearing from multiple professionals, hobbyists, and my own formal education on the matter I believe that my methodology, not the tool, was the issue.

The torque wrench I was using was a 1/2" drive torque wrench. The problem still wasn't there. The issue was that I don't have 1/2" drive bits for the bolt sizes on the cylinder head studs. So what does that mean? I threw a 1/2" to 3/8" drive changer along with a deep socket (can't remember why, but I think it was necessary; this has been a few years). I know there was a bit of slop in the chain of mechanisms to the torque wrench drive mechanism. The slop also caused me to have to support this collage of bits in order to turn the wrench.

After seeing multiple YouTube videos on torque wrench usage and thinking about the geometry that could result from my methodology, I'm rather certain that my purchase of a 3/8" torque wrench will allow me to put a proper torque on the bolts.

Hopefully all goes well and I can clear the vendors in my mind of supplying sub-standard head studs and my poor work practices!

Thanks for all the soundings in the previous threads. It certainly provided the thoughts I needed in order to truthfully evaluate what I was doing right and wrong!

J DeRienzo

J - Using an extension on a torque wrench will not effect the accuracy of the torque applied to a bolt since the torque is still being applied at the wrenches calibrated center. the only thing that will effect the torque being applied is the use of a crow's foot, which will place the bolt almost an inch beyond the center of the wrench's torque center (this can be worked around, but is difficult to explain on the forum). The 3/8 drive wrench may be a bi more accurate in that you will be using it closer to the center of its range than on a 1/2" drive wrench which will be working closer to the lower end of its range. Any torque wrench can and should be recalibrated periodically by sending it back to the manufacture, who will calibrate the wrench for a nominal fee. Checking it against another torque wrench is not an accurate method of calibration. Cheers - Dave
David DuBois

Is there an easy way to check the accuracy of your torque wrenches? Also, does anyone know where you can purchase a "Beam" type torque wrench (as opposed to the click type)? Thanks and have a good day!

John Progess

Any tool store should sell a beam torque wrenceh, as well as Sears, KMart, etc.
An easy method to check is never easy. A beam torque wrench can be checked with a known weight at 1 foot from the fulcrum(from the 3/8 or 1/2 inch drive male connection.) This should show the torque on the wrench in foot lbs.
A click torque wrench is tougher to check.
Mike Parker

I have to agree Mike, relatively simple to check although why do you suggest the click type is any different. Surely the same method applies except you are looking for a click.

The only things you need to do are find some known weights 50lbs worth would be good.

Weld an old socket to somewhere strong so that your torque wrench can be put into the socket and hang to the side horizontally. Then measure a foot from the centre of the socket square.

With a beam type hang your 50lbs at a point 1 foot from the centre and note that the deflection is about 50ft/lbs indicated

With a click type set it at 55 ft/lbs and apply the 50lbs load the same. Should not click (make sure the load is applied gently) now reduce the setting by a 1lb and try again. Repeat until you hear a click, hopefully both will be accurate.
By the way a lb or 2 either way would be considered accurate and how good were your "test" weights?

Finally many torque wrenches are longer than a foot. If you can go to 2 feet from the centre then only half the weight is required. Hopefully everyone can do the simple maths for other lengths.
Bob England

Hold the square end of the wrench in a vice. Use a length of ABS pipe over the wrench arm to extend it and use lighter weights. I used a pail of water. weigh the pail and water on a bathroom scale. Hang it from the pipe using wire. Slide the wire out until it clicks then measure the distance from the centre. Make sure the pipe is horizontal. Allow for the torque of the pipe weight (1/2 length x weight. I agree with Bob, same set up for either type.
Art Pearse

Actually Art water is a good calibration medium. In heavy industry many high capacity weigh systems are calibrated using high accuracy flow totalisers to measure how many gallons of water are in the vessel.

Fortunately here in the UK a gallon of water weighs 10lbs, in the US it only weighs 8.35lbs, must be the sunshine :-)

I am not sure I would have too much confidence in bathroom scales but measuring a gallon of water accurately can't be too hard.
Robert (Bob) Midget Turbo

"Fortunately here in the UK a gallon of water weighs 10lbs, in the US it only weighs 8.35lbs, must be the sunshine :-)"

Not the sunshine, it just sloshes out of the bucket on the trip over here ;-) Cheers - Dave
David DuBois

Does anyone know if a gallon of water with a high iron content, weighs more than 10lbs. or8.35lbs US?

George Raham
G. L. Raham

The difference with a click-type torque wrench is that you have to know that it clicked at the weight you are measuring, and not before.
therefore you must have a weight at the desired weight, one somewhat heavier and one somewhat lighter to insure that it does click where you want it to and not where you don't want it to. A beam reads the torque so you know exactly what you have.
Mike Parker

Mike did you read my post?
How you do it is to adjust the torque wrench set point. Say you are applying 50 ft/lbs then set the wrench at 55 then 54 then 53 etc. You can do it Mike!
Robert (Bob) Midget Turbo

Bob, I leave calibration of my click torque wrenches to the guys with the machinery to do it properly. keeps me out of trouble.
Mike Parker

You can test a beam type by clamping the square drive in a bench vise. All the beam types that I have seen have a pivoted hand grip and any load should be applied at that point as the beam is designed to bend when loaded there. Mine has a distance of 16 7/8" from rotation axis to grip pivot so I would load it with 12/16.875 x load. If done vertically the handle adds less than a pound to the vertical load (10oz. by test).
John DeWolf

This thread was discussed between 27/12/2009 and 28/12/2009

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