dfinnegan

I'm having a bit of trouble locating a 340 ft-lb torque wrench.

I own a 250 ft-lb torque wrench and am considering fabricating an extension to allow me to use this wrench to achieve the 340.

Any one have experience with this?

Comments pro or con?

The paper work that came with my torque wrench outlines the calculation necessary to correctly use the wrench with an extension. Basically, length of wrench center of head to center of handle (it's marked); call this L, plus length of extension (E) divided by L gives the multiplier.

T(extended) = T (wrench) * (L + E) / L

The extension I'd fabricate would be a cheater bar (1" ID pipe) over a 1/2" breaker bar handle. The extension would have a half inch socket adapter welded near one end of the pipe. The other would have a set screw to secure the pipe to the breaker bar.

Very similar to This write up.

What do you all think?

Geoffrey

I'd just purchase a 3/4" torque wrench and an adapter to 1/2" if need be.

ddubois

What are you torqueing to this level? I'm guessing the rear axle nuts? If so, I would suggest doing a simple torque wrench consisting of a breaker bar, pipe extension, and simply stand on the horizontal bar at the appropriate distance based on your weight. This was my technique back in my 'poor student backyard VW repair' days.

warmfuzzies

Torque is simply Kg/NM or lbs/ft, simple really, if you have a one foot torque wrench, then a two foot one will give twice the torque for the same effort. We use extensions for a different purpose at work, but as they are made for the job, like crows feet etc its easier to work with.

The above is essentially correct, but as Geoffry said, get a bigger one.................it's safer than making one.

Kevin

MisterRisky

I think a little torque wrench extension is a great idea. I think that buying a rather expensive high torque wrench for rare use seems extravagant (not that I often balk at buying tools).

I've had a little bit of experience with this when I was younger. Here's my very limited thoughts:

Make an extension that is just long enough to get you the increase you need. Since you need, roughly, 350 out of a 250 extension, don't triple the length of your handle. The sacrifice is precision. Also, its a good idea to keep the math simple. You don't really want to have to multiply the reading on your wrench by 2.643465 to get the outcome. Since you need only about 40% more, just make your extension double your existing handle length. Then you can simply divide the desired measurements in half. If you want 340, use a doubler and set it at 170.

Seems like a solution that is both elegant and inexpensive. Although I have to admit, Doug's "(m)*** and lever" approach is the approach I am most likely to taken when I torque heavy nuts. But I am an economist not an engineer.

dfinnegan

JD,

You comments are pretty much right in line with my thinking. I don't like the idea of spending quite a bit of money on a wrench that I'll likely use just a couple of times. Prices look to be $4-500.

I also thought that making the math easy and only going far enough to get the torque I needed was right on. I was also thinking that I should get into the meat of the wrench's range so that it is most accurate; given that I'm effectively doubling the error.

I was mostly looking for some input on how important it was to get exactly 340 ft-lbs, as opposed to 344, or 333. I figure I'll shoot for at least 340, and accept a few pounds over given the extension and loss of precision.

I figure I'll be better off than standing on a bar, but not as good as getting the correct tool. I was looking for some feedback on the error.

Thanks.

dfinnegan

Actually, looking at the specs for my wrench it is +- 3%. Doubling yields +- 6% or 10 ft-lbs.

So, 330-350 is where I'll end up.

stevepaa

No, torque wrenches work off the moment induced in the head. Adding an extension to a torque wrench set at 170 ft lbs will just give you 170 ftg-lbs at the head but will require less force(weight) to do it.

Either use a torque wrench set for 350 or use a breaker bar with long extension and calculate the exact point for you to stand on it. Be sure the extension is level with the ground as it is the force that is normal (perpendicular) to the arm that induces the torque at the head. Just like ddubois suggests. Then go to your local porsche mechanic and have him redo it correctly. All of 5 minutes of his time, and my guy does it for free.

MisterRisky

Steve, I mean no disrespect, but did you read the link that Dave gave? Your answer makes me think you suspect Dave is talking about adding a cheater bar to the handle end of a torque wrench. He's not talking about a cheater. He's adding an extension to the torque end which does amplify the torque at the nut.

However, your advice on asking the mechanic to torque it down proper is good advice.

Dave, WRT error, I can't imagine 10 ft lb mattering much. I doubt that 10 pounds too much is going to damage anything and I can't imagine that 10 lb too little is going to allow the thing to come off. But then again I am king of measuring with a micrometer, marking it with chalk, and cutting with an ax.

springer3

Understand that torque is not really what you want. You want clamping force to be approximately 50% of yeild of the fastener. Torque is a pretty crude way to get bolt force. Weigh your self, stand on the cheater bar at the correct distance, and you will be as good and possibly better than an extension bar between the torque wrench and the bolt.

stevepaa

oops, sorry. I did not look at the link. Yes, that does work. Just note that if you do not keep the torque wrench in line with the extended arm, the delivered torque is less and gets less very quickly.

However, the weight of the extension probably adds enough to compensate for being off a little.

Heirsh

My local auto parts stores will rent tools for very reasonable fees. You may want to check into this.