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Discussion Starter · #1 ·
Versatile Torque Wrench

Link to other parts of the project
http://forum.e46fanatics.com/showthread.php?t=899347

I haven't seen anything like this posted before, so I'll put it up.

In a moment of brilliance, I decided to leave my torque wench back at home in another country due to me doing some work on my wife's car that we use back there. As soon as I got back here, I asked myself WTF I was thinking. Without a torque wrench, rebuilding an engine would be a difficult task. Also, I had been looking for a torque wrench that would do both left and right hand threads, as well as something that would handle the high torques that are required on different components. I was going to be up for a good amount of cash.

This is my solution.





How does it work? For those who did high school physics, you probably know what I'm going to say, but for those who didn't, here is the physics lesson.

Torque is turning moment, or in simple terms, twisting force. The amount of twisting force that is applied is a function of the force, and the distance from the fulcrum the force is applied. The torque is the force multiplied by the distance. Simply, if you hold the wrench 1 foot from the bolt, and you apply a force of 1 lb, you are applying a torque of 1 foot pound. This is the same as if you apply ½ lb of force, but you have a longer wrench, and you are applying the force 2 feet from the bolt.

What are Newton Metres? 1 Newton is the force required to accelerated a mass of 1 kg at a rate of 1 metre per second squared. Therefore 1Nm is the torque when you apply a force of 1 Newton at a distance of 1 metre.

This all sounds a bit complicated. All you really need to know is that 1 kg = 9.8 Newtons. So if you apply a force of 1kg at a distance of 1 metre, you are applying a torque of 9.8Nm

So how to use this?
Measure the distance from the socket to the part of the wrench you are going to apply the force. In the photo above it was 17cm. ie 0.17m. We will call this 'd'

The bolt I'm torquing is one of the cam caps. Required torque is 14Nm. We will call this T.

The force I'm going to apply is what we need to know. I'll call the force F.

As we saw before, the torque is equal to the force multiplied by the distance.

T = F x d or rearranged, F = T/d

The problem is the force is in newtons, not kilograms. We saw before that 1 kg applies a force of 9.8N.

So if the weight applied is W, then F = 9.8 x W

The above equation becomes

9.8W = T/d or W = T/9.8d

This gives us the weight in kilograms that needs to be applied to achieve a torque of T, when applied at a distance of d.

In the above example I need 14Nm, and the distance is 0.17m.
The weight I need to apply is 14/(9.8x0.17) = 8.4kg

So applying a force of 8.4 kg at the distance of 17cm gives me an accurate 14Nm.

As explained the scales used are normally used for weighing baggage. They weigh up to 50kg, and cost less than $10. They worked extremely well applying an accurate force to the wrench.

So how is this useful? I'm certainly not going to throw away my torque wrench and use this instead. It's definitely less convenient. However, most torque wrenches only work on standard direction threads. For left hand threads you need to buy another torque wrench, or guess. There are two left hand threaded bolts on an M54 engine. The small bolts that hold the vanos pistons in, and the nut that holds on the oil pump sprocket. Both are clearly critical, especially the oil pump nut. There have been a number of failures of engines due to this nut coming off. The best thing you can do to avoid failures is to torque them correctly. Spending a bunch of cash on a specialised tool that you will seldom use is not what most people want to do, so this is an alternative.

Also, this works equally well for bolts that need lots of torque. For example the bolt that holds on the vibration damper needs 410Nm. On later model engines it's 600Nm. A tool to do this is going to cost a lot more than your stock standard torque wrench. The above can be easily applied to this type of torque.

To get 410Nm, using the above equations, you need to apply a weight of 41.8kg at a distance of 1m, or 20.9kg at a distance of 2m. Very manageable using a long breaker bar.

Also, this can be used for tightening something you can't get a socket onto. For example, each of the vanos solenoids can only be tightened using an open type spanner. Using this method you can easily torque it correctly. There are countless sensors and bolts like this that can't be tightened using a normal torque wrench, and can easily be torqued correctly by this method.

An additional use is checking the calibration on your torque wrench.

This method works best for bolts that are in the orientation shown in the photo. None of the weight of the wrench is torquing the nut, it's only the pull on the scales. If the wrench is vertical (ie the bolt is horizontal) the wrench handle needs to be in the 12 or 6 O'clock position for this to work accurately. If it's in the 3 or 9 O'clock, the weight of the wrench handle will either increase of decrease the torque applied.

For conversion purposes, using 1 foot = 30cm, and 1 kg = 2.2 lb
1ft lb = 1.36Nm

If you are used to using ft lb, get the Nm, and divide it by 1.36.
In the above example of the cam cap nuts (torque required = 14Nm), 14/1.36 = 10.3 ft lb
Using the same theory as above, you can now measure the length of your wrench in feet, and then work out how much force in lbs that needs to be applied.

Hope this helps some people.
 

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Discussion Starter · #4 ·
You might think it would slip off, but as long as you are pulling 90 degrees to the wrench it won't move. I thought I'd have issues, but even on a bare breaker bar with no grip, I just marked with a marker where I wanted to have the strap, and no problems. I've done a bunch on stuff on the engine using this method. Cam bearing caps, Crankshaft bearing caps, large torque and small. No problems at all.
 

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Can't believe you aren't getting more recognition...
I guess folks were never stuck without tools mid-job...
I've always wanted to check my torque wrenches and even wanted to send them off for calibration, but this is a great way to check for yourself!
Anyways. Bravo!
 

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I've seen this done before with fishing scales. Seems to work well and was considering trying it for my hub nuts.. because a 3/4" torque wrench is $$$. Another method I was considering is the standing on bathroom scales method. Obviously that method only works on horizontal bolts.
 
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