The Deputy

By all means use it...obviously you thought you needed it...and if you haven't done a lot of mechanical work on cars...all the better to use one...but still using common sense must prevail and if something doesn't seem right...stop...and use caution to advance any further...or down-grade the torque value according.

Personally, I'd rather tighten a bolt later that didn't get torqued to specs (or didn't feel right, while torquing by feel) and starts seeping...than repair an issue like pictured in the two topics supplied by "Fogey1". I've stripped out far fewer bolts by backing off...then the ones I proceeded with.

I equate it to this...does a writer sit with a dictionary in their hand checking every word as they write each sentence...no...they use it when they need one.

Same goes for a well-seasoned mechanic...he knows when he needs one and when he doesn't.

Good luck, with your oil pan job.

Brian.

The Deputy

I'll try and keep this simple...since it actually gets pretty intense if you do the math on different lengths and hardness of extensions used.

Anyway, if you use an extension on a torque wrench...the extension absorbs torque by twisting, the torque absorbed by this winding/twisting of the extension never makes it to the bolt or nut. However, the torque wrench feels the resistance of the winding/twisting and takes it into the equation.

So, lets say you use a six inch extension on a bolt that must be torqued to 100 foot pounds (I don't have my chart...it's in my tool box at work...so this is just from memory), most likely you will be only applying possibly 85-90 foot pounds when all is said and done..and possibly less torque if you are not using a quality extension (like an impact extension).

If I'm torquing head bolts...normally I never use an extension longer than two inches...and add about ten pounds of torque value.

Brian.

bureau13

You're talking about extensions on the "business end" right? As described above? For some reason, I was thinking about handle extensions, probably because I've been needing them lately. What you said makes perfect sense for the normal types of extensions.

The Deputy

Yep, business end. I missed the part about "handle end" in your earlier post. Never really heard of anyone doing that...so my mistake. I can not see how adding an extension to the handle would change torque value...but I'm not exactly sure...since I've never attempted this.

Brian.

bureau13

Well it won't change the value seen by the wrench, but it requires less force to get there, as it's a longer lever arm. There's no reason to do this when using a torque wrench to tighten something of course....just when using a wrench to break something loose....so I'm not sure why brain even went that direction. Sorry for the confusion!

dr bob

So... what happens to the torque in the extension that causes it to diminish? If the elastcicity of the extension absorbs the torque at one end, the other ened will have that same torque, plus the motion as the spring unwinds.

Think of it this way: If I have a coil spring (that weighs 1 pound) and I put a ten pound weight on it, as I add the weight, the spring will deform until the weight is born by the spring. How much pressure is on the support for the spring? Answer: 11 lbs. (1 lb of spring and ten pounds of weight. The extension bar is just like that spring, just not coiled up.

There is a lot of junk science that says otherwise, but at any time (was going to say 'moment'..) the static force on one end of the spring will equal the static force on the othere end.


All that said, I use the stiffest extensions I can when uing the torque wrench or any other ratchet or bar. Why? Because the dynamic force applied can be different. Right up to the point where a fastener yields.

Hilton

The drain plugs are pretty obviously a wrong spec - with only something like 4 threads of engagement, if you torque them to spec, you're going to tear the threads out of the block. There was a post by GB about it a couple of years ago too IIRC? I'm in the camp of a bit of teflon tape and firm by hand, plus a check for leaks.

However, there's a reason I own um.. 5 torque wrenches, in varying sizes. I torque pretty much everything to spec on the car otherwise.

The most nerve-wracking bolts on my S4 to torque to value are the Cam cover shoulder bolts.

GregBBRD

We (my shop) torque everything, except screws. From the 5mm hardware to the biggest threaded fasteners in the transmission, we torque it. I own 11 different torque wrenches....at work, alone. Of those, I actively use 7 of them....two different calibrations of inch pounds, two different calibrations of 3/8"', two different calibrations of 1/2", and one 3/4" one.

I can probably can get within 15 foot lbs on 8mm and 10mm hardware (always too tight), but after about 100 foot pounds, I can't get close. It's easier to just grab a torque wrench and use it for everything, for both Grant and myself.

BTW Dave: Completely agree with you on the block drains.

dr bob

Greg, man you are missing out! I have the cutest little Japanese Tokiko torque screwdriver. No need to let the non- hex and Allen head bolts suffer in isolation!



For those who don't know, Greg is probably the most religious user of torque wrenches that I know. Also the most religious about cleanliness, attention to detail, and disdainer of "that's probably good enough..." I learn at the feet of the master.

jon928se

This is just plain wrong. If you apply a set torque to the torque wrench end of the extension and the bolt or nut in the socket at the other end of the extension doesn't rotate, then it (the nut or bolt head) will see exactly the same torque applied at the torque wrench end of the extension irrespective of how much the extension twists. Without wishing to go into Kibort territory or parrallel universes this is an unarguable law of physics.

Sure, the more elastic the extension is the more twist will happen in the extension until you get to that desired torque but you will get there eventually unless the extension is made from spaghetti.

Where the above doesn't apply is using an impact wrench and "calibrated" torque extensions that rely on the elasticity of the extension to limit the torque applied by the hammer blows of the impact wrench. This is a dynamic scenario that just isn't applicable to the above. And furthermore for those "calibrated" extensions to work properly they have to be matched to the impact wrench being used. This doesn't often happen.

What should probably be said in the context of this thread is that the use of thread lubricant (and PTFE plumbing tape is a thread lube) results in more torque being applied to the threads (of the bolt but not the head) than would be the case if no thread lube was used. Depending upon the bolt/nut/type of washer etc etc, the torque applied to the threads can vary from about 50% (no lube anywhere) of the torque applied to the nut or bolt head to about 85-90% (everything lubed with a near perfect lube). So reduce the torque if you are using lube where none was specified and stick to the WSM regarding lube or no lube for things like head bolts even if they are specifed as angular tightening not lbs ft

The Deputy

This article by Hot Rod magazine and Snap On somewhat touches on the subject...and mentions using only the shortest extension while torquing. I wish they would have elaborated more about "why" you should use the shortest extension possible...but they didn't. Also, craftsman use to have a chart on this subject...but I can't find it on line.

http://www.hotrod.com/how-to/additio...-wrench-myths/

I'll have to wait until I get to work to dig out the extension torque chart I have.

I guess a person could just go out and torque some bolts, with various lengths of extensions and without...and see what they find out.

Yeah, I get all of this...and the crowfoot stuff mentioned earlier, too.

Brian.

Adk46

Some fascinating (that is, nerdy) stuff about torquing:

The objective in serious situations is an axial stress in the fastener that produces a static preload across the joint of the parts being fastened. The relationship between the tightening torque and this preload would be simple if the system were friction-less. Of course, there is friction, both in the threads and at the head/washer of the bolt, affected by thread engagement, lubrication, plating, corrosion and how your garage refrigerator is stocked.

Thermal expansion may be important, too, either from differences in temperature among the three parts (counting the bolt), or from differences in the thermal expansion of different materials (known as "alpha"). Walk up behind a gas turbine engineer and whisper "delta alpha - delta T" and watch him flinch.

The more serious the application, the more elaborate the torquing procedure.

But sometimes the only objective is to keep a bolt from backing out, where the loads are not high and fairly static. No need for a torque wrench when you assemble your gas grill.

There are other situations where the objective is not force, but displacement. Gaskets and crush washers need to be squeezed a certain distance to make a good seal. This displacement is related to the torque on the fasteners, of course, but when you see instructions like "hand-tight plus a quarter-turn", the engineer is hoping for a certain displacement. Hoping.

This load-displacement thing might get turned around, though - big bolts might be heated to a specific temperature and installed with relatively little torque, counting on thermal displacement during cooling to apply the preload.

Adk46

My guess, regarding the extension issue: you want only torque on the extension. If you are wrenching with just one hand, you're putting a sideways load on the bolt, or something complicated that will mess up the torque measurement. Most of us will use two hands, of course, attempting to remove the sideways loading. The longer the extension, the more difficult this becomes.

dr bob

So are numbers different if I use a deep socket vs a standard socket on my torque wrench? Is that better or worse than using a 1" extension?

Adk46

Sorry, I have to go out to the garage for another Old Hypotenuse. errrp. Back in a moment.