1/2in drive torque wrench with 3/8 adapter + 3/8 extension
 

i used it to torque my head studs down, and im wondering would this give me an inaccurate torque reading? sorry if its a stupid question but id rather not blow a head gasket.

Yeah... I'd go about 50lb beyond spec, just as a guess. The more connections you make, the more torque lost, and you are also using a thin 3/8'' extension, which will for sure twist. How long is it? Ideally for that kind of job, you want all 1/2'' stuff, beefier and less likely to twist and bend.

Torque is not "lost".

If the wrench says 100 lbs, then 100 lbs is getting to the fastener. Just keep everything straight and avoid wobble-adapters.

...good point. :bowrofl:

Well my point stands... your getting some twist, so why work yourself harder by having to push that wrench an extra 1/16 rotation...

But couldn't all of that extra flex in the "line" make for inaccurate readings? The wrench may be seeing the torque, but the fastener could be binding and not getting that extra little bot to pop it a little further around. Especially with longer, 3/8'' extensions. Either way, It's ideal to use larger tools in higher torque situations.

I just assumed you were being mean.


"...on second thought, probably 100lbs over spec to be on the safe side...just don't use a metric torque wrench on an SAE bolt, that'll really mess things up."

i used a 6" 3/8 extension.

should i use a 1/2" extension with the adapter? the problem is i dont have a 12 point socket thats 1/2 inch drive.

or should i just go hunt for a 12 point socket thats 1/2 drive. ive never installed a head before sooooo again sorry for my noobness

My point that I was trying to make. Even with a lot of assembly lube, a lot of higher torque bolts will still bind and "pop" as they get close to their specified torque, especially if you stop mid turn and start again. If you have a smaller extension and a bunch of thrown together fittings, The wrench may read specified torque, but you could also go 20lb beyond that and not have the fastener move at all. So when using smaller tools and more fittings, your accuracy range is broadened. If you stop 30lb under a 200lb spec, and start again and go to 200lb on the wrench, the bolt could still be sitting at 170lb and it was bound by friction and never jumped to 200lb. Maybe that did a better job at saying what I meant to say. So just because the wrench sees x amount doesn't mean the fastener is set to that amount of torque. The more flex in your extension and the rest of your tools, the further off your readings will, or can be. Though I guess it can still bind the same, and as much with a correct tool (1/2'' drive) but it's more precise and easier to do, not all of that flex messing you up.

^ this guy seems really sure about that answer.

im going to double check with the 1/2 inch drive extension and adapter and see if it takes it any further before it clicks. i feel like with the larger shaft it will apply more torque, cause i know when it comes to torquing wheels down with an air gun, most shops use torque sticks with different diamiter shafts.

That's kind of what I was meaning with my first post, the torque stick example. The gun is still putting the same torque out, but the stick absorbs shock, lessening the torque. Of course there is no shock in your hand tools, but the binding of the bolt/washer to the head surface can be somewhat like shock when it grabs and releases. With a longer and thinner extension, you will feel less pops, less often through a rotation, as the shaft flexes and builds up or loads, then releases, a thicker and shorter extension, you will feels a lot of much smaller pops/clicks, more often, since it flexes less. Just makes it much easier to me, and more reassuring that it's correct.

If the wrench says "100 ft lbs" then 100 ft/lbs is being applied to the fastener.

100 ft/lbs is 100 ft/lbs whether the fastener is "sticking" or not. If you "bump" the wrench to overcome this, then you exceeded 100 ft/lbs in doing so.

Turning the wrench to 100 ft/lbs deflection and then holding it there for a second will have precisely the same effect on the fastener regardless of whether or not there is an extension between the two, or of what diameter and length the extension is.

This is a whole different affair from using those twisty-sticks with an air gun. Air guns do not apply continuous force.

k thanks guys!

But what about the friction between the fastener washer and the mating surface of the head? Just becuase you are applying the torque to the fastener head, doesn't mean it's turning the fastener deeper into the threads, so when you let off, it will return to the last place it "popped" which might be 5lb under, or it could be 20-30lb under spec. I've never used a perfect, friction-less lube before... if the fastener is binding, you can add more torque, but it's only applied for as long as you push/pull the wrench handle. If the fastener never actually turns, the torque is not actually applied. Of course this is negligible in most cases, but the higher the torque spec, the more noticeable this becomes. Or maybe I'm wrong... just seems like this friction would play a part in making a torque specification less precise over a given range.

You are correct.

(Well, you're wrong in that the torque IS applied, it just doesn't result in any useful work being done. Think about trying to push a boulder that weighs 10,000 lbs across a dirt field. You're not likely to actually move the boulder, but you still applied force to it.)

However this effect will not change based upon whether an extension is used between the wrench and the socket.

But... as I said before, if you use a thin, long extension, you will be able to twist the wrench maybe as much as 1/8 turn before the friction is overcome, and the fastener actually rotates. Using a shorter, and thicker/stiffer extension, you will have less twist, and the "jumps" will be much smaller, and you will be more precise, will you not?

Just seems like to me, having a fastener breaks loose with a wrench/extension with 1/8 rotation of twist on it would be far less accurate than one only breaking free with 1/128 twist/movement. Narrower range for error.

Again, negligible, but still..... Give me the choice of 1/2'' drive torque wrench with no extension, or a 1/2'' drive wrench with 1/2'' to 3/8'' adapter and 3 12'' extensions and a deep well socket, I'm going with the one with less twist.

^and applied was the wrong word. I'm never good with finding words. It's almost like I don't speak my native language fluently :fawk:

This reasoning would also conclude that flex-beam torque wrenches are inherently inferior to click-type wrenches, whereas most everything that I have read (including from the NIST-certified crowd) would seem to argue that this is not the case.


Agreed. Far easier to keep everything aligned.


OP: Do you have a 1/2" extension? If so, put that on the wrench and then put the 3/8" adapter on the end of it. That should keep everyone happy.

Not really. Because one is a lateral force applied to a shaft. The other is a rotational force, involving touching objects with friction in the mix.

But yes, I'm done.

Damn, you guys are confusing each other.

OP, it doesn't matter if you have 30 feet of 1/4" extension, or no extensions and a short socket on a 3/4" drive, 100ft/lb of torque on the wrench will equal 100 ft/lb of torque on the fastener - just don't use U-Joints.

Yes, the 30 feet of 1/4" extensions may twist a full 360 degrees at 100 ft/lb, but there is still 100 ft/lb of torque on the bolt - you will simply have to turn the wrench an additional 360 degrees before your torque wrench shows 100 ft/lb because you must also stress the extensions to 100 ft/lb. Any amount of movement in stock washers/metal to metal friction/etc. has been accounted for by engineers that make way more money than me.

I don't think either of you are understanding what I am saying though, at least maybe not fully. If you tac a weld on the bolt head and head mating surface, you can wrench all you want, it it may say 500lb/ft, but once released, that bolt will still have no holding force on it, other than the weld. Of course that is a far exaggerated example of friction, but maybe that puts your brain on the same track as mine. As I said earlier, even with assembly lube, there is still friction, and the fastener does not always move smoothly, reacting to every input you make with the wrench handle. Just because you turned the wrench until it said 100lb/ft does not mean the final torque on the fastener is within that 100lb/ft spec. And as you have pointed out, that is accounted for by the well paid engineers, but a level of inaccuracy is there, as with all measuring devices. By using more flexible tools, or longer extensions allowing for more twist, you are only growing that margin for error. Like I said, with a lot of twist in an extension, you have no idea if that bolt is going to pop free and catch up to your wrench, putting it in correct spec, or if it will only pop free and maybe 1/4 rotation to your full rotation (again exaggerated) before again being held by friction, short of your spec. You can virtually eliminate this by giving less chance of this load and pop free, for lack of better term, by using a more rigid, shorter extension which will flex far less. I have myself torque things with a similar setup to the OP, a 3/8'' extension on a 1/2'' wrench, because I did not have either the correct extension or socket. On a 100lb/ft bolt, that extension could twist probably end to end by a full 1/16 of a turn before overcoming friction, having it pop loose and left to it's own ways until friction stopped it again, who knows where. Had I used a 1/2'' wrench, with a short 1/2'' extension and a proper socket, there is going to be no where near as much twist or load before the fastener pops loose, probably 10x less twist. Meaning when the fastener does decided to break free from the friction holding it, it has less room in that arc your wrench covered to end up in, so you will have more precision over the final stopping point of the fastener.

All of that was very unscientific in definitions, but that's all I have. ;) Plus I'm bored.

Yes, I know I am sort of grasping at straws, and my argument is minuscule, but it's still real, damn it!!!

Another thought on the original point. Think of you getting your flexible torquing setup right at the specified torque you are shooting for. The extension may be twisted a full 1/4 twist, but it doesn't matter, because indeed you are at the specified torque. But then right as you are about to let off after you hear the click of your click type wrench, the friction gives way and the bolt turns another 1/8 turn. If you go back and measure again, you are now again under torqued by a pretty sizable amount, because the twist load on the extension was accounting for some of your final torque value. Had you not had that twist, and had been using more solid tools that didn't twist, you would not have had that chance for error. Of course in a perfect world where assembly lube negated friction completely, this would not be a topic of discussion, but there isn't a perfect assembly lube, and there is friction, often lots of it. After all friction is what we are after, since it holds engines together. Well the bolts do, that use friction...

Maybe after all of that, my point is more clear.

I've never met a 1/4" extension or adapter that would handle 100 ft/lbs of torque, what brand are you using? :laugh:

OK, here we go. Finally I have formed something coherent in my mind that will actually describe irrefutably what I am saying is correct. Your wrench says 100lb/ft, the bolt actually stops due to friction at 50lb/ft. So why are you seeing 100lb/ft at the wrench? The extension is acting as a torsion bar, feeding your wrench that additional 50lb/ft it requires to click. So you go back and check with a wrench with no extensions, and oh no! It's only half of the torque you wanted. Remove the torsion bar of an extension, and you transfer 100% of the force, or close to it, to the bolt.

Which is why I always over-torque bolts, at least the larger ones with bolt heads or built in washers with a large surface area. Torque specs were done in a lab of some kind, or in controlled environments with ideal equipment. Adding anything that flexes on the work end of the tool WILL skew the results.