When using a torque wrench you can not always reach the part you need to tighten. If you add a 4" or 6" extender is the torque value still accurate?

Yes

I'm no engineer, but I would say yes. You could use an extension a mile long and it won't change the value. Even if you lengthen the handle, it just makes it easier to turn, it still clicks at the required setting.

Sorry to disagree.

The value at the torque wrench will be the same. But the value at the other end of the extension will be less. The extention WILL absorb some of the torque instead of transferring it to the socket.

You can see this effect in front wheel drive cars. When they have unequal length drive shafts, they can torque steer. This is due to the torque loss throught the longer shafts. There are several methods to compensate for this in FWD so not all do it, but it is a factor.

Try this. Put a bolt in a vice with the treads up. Use something fairly heavy. Put a nut on the bolt and run it down. Now put a long extention on your torque wrench, and tighten it down to 100 foot pounds torque.
Remove the extention, and with just the socket tighten it down again.

You will see the nut turn further to reach the 100 ft lbs. This is due to the torque loss of the extention. The torque wrench was at 100 both times, but the nut was less the first time with the extention.

Another way you can see this is by using a long extention and trying to loosen something very tight. You can see the extention flex. This is more apparent with a thinner extention. A 3/8 drive really shows it well.

I have had many instances where I could not take a nut loose with an extention, and by removing it, I could take the nut off.

It happens quite often with impact wrenches. If fact, tire shops uses special extentions on the end of the impacts to control torque and only tighten the nut so far. After that point, the extention absorbes the impact, and the nut stops tightening. Granted, this is a special extention called a torque stick with a special limit in mind. But the effect, to a lesser degree, is still there.

Some research into engineering data can reveal general guide lines for the amount of torque lost through a shaft.

This is one of the reasons driveshafts are hollow. A hollow shaft resist torque loss more than a solid shaft. Buy making the bigger and hollow, instead of smaller and solid, they can handle much more torque without twisting.

Bottom line, it makes a difference. How much depends on the length and size of the extention, and the amount of torque applied. The more torque, the more loss. In some conditions you can lose between 10% and 20%, but it could be much less. There is ALWAYS some loss.

Ken is right on ,any time you add an extension or a CROWS FOOT to a Torque Wrench ,you change the value of the reeding,whether its the old stile pointer wrench,or the new stile clicker wrench,or even the digital ones

yes we had this discussion about crow foot wrenches on torque wrenches when we talked about AN fittings

the general consensus with it was that the loss is fairly minimal. and probably not worth compensating for.

but on socket extension I would definitely agree with ken.

I have twisted way too many 3/8 extension in half to ever disagree with him on this.

I generally increase the torque 5%/ft of 3/4 drive extension, 10%/ft of 1/2 drive ext, 20%/ft of 3/8" to compensate

and before anyone disagrees with my figures.. this is just a good rule of thumb I have observed

|UPDATED|11/17/2004 3:05:00 PM (AZT)|/UPDATED|

I like Ben's rule of thumb. I would say that those figures are for a 10 inch extention. Shorter would be less torque loss, longer would be more loss. But this depends on the quality of the tool. The same size will vary greatly between brands of extentions.

A crows foot is either going to add to the torque or subtract from the torque. It depends on the angle of the crows foot to the head of the ratchet.

Well, once again Keester comes thru.
Sorry for talking of which I know nothing, and thanks for setting us all straight. Next time I'll shut up if I'm not sure.

To answer your original question,if you are torquing your head bolts with a 1/2" drive 4 or 6 inch extension there will be no change. A crows foot changes the rotational center but this is a different issue! It is true that using a 3 foot long 3/8" extension would twist is correct but you would never do that! Let's get real here and give people usable information.
Steve