I am helping a friend rebuild the front end of his E-Type and we were doing up a number of 1/2" bolts, some into captive nuts some with nylocs but most used spring washers.

Using my torque wrench we encountered some oddities - well seemed odd to me;
1 Some of the non captive bolts would go to torque with a clear click with a spanner on the nut but I could still rotate the nut & bolt in the hole. Put a spanner on the nut and the wrench would click. I assume the nut & bolt are at the correct torque but can somehow rotate in the hole at the same time. Doesn't make proper sense to me.
2 Where we had spring washers it seemed to me subjectively that although the torque clicked the actual 'pinch' in the hole varied. Quite subjective but definitely felt that way. Personally I wouldn't use spring washers but not my car.
3 One longer bolt sheared despite not reaching the torque. My friend said he felt enormous torque on the spanner he was using to hold the nut but my side was fine. Baffling.

We agreed we didn't trust the torque wrench any more so stopped.

I went home and tested my wrench against a friend's on wheel nuts done up to various torques and they seemed consistent. Then I realised using one of the hand held luggage weight measuring things I could do foot pounds on the torque wrench. So I set it to 25 ft/lb say, placed the luggage strap one foot from the centre of the wheel nut and lifted to the click and it was as the dial on the wrench +-10% say which seems OK.

What am I not understanding? Clearly I'm doing something wrong. Or I'm being dim.

Mike

 

Not dim by any means.

My thoughts from down here and Midnight.

The bolts in question have a length of thread at the end, then a plain shank to the head, OK.

My brain thinks?? you are running out of thread, and the nut is TIGHT, as it is at the unthreaded shank, but clearly not crushing the components as required.

Couple of flat washers, shorter bolts will sort that IF that is the reason.

The fact he had enormous twisting forces when holding the nut also adds to that.

Lets know please.

 

Thanks Grant, that's good thinking. One bolt at least had a smooth shoulder for part of its length. We can check the broken one.

I am still a bit confused about how the springiness of the washer would change the effectiveness of the torque wrench setting.

 

drmike, many years of my life were spent having to know more about torque than I care to admit to.

Like was said, the bolt that you took to the desired torque, yet was still spinning in the hole was most likely bottomed out on the shank, hence why it reached a torque, but it still loose. I would remove the nut off of that bolt, insert the bolt fully into the joint and see if the shank is sticking out at all. The addition of a washer or two may be all that is needed for that joint.

Now for why a bolt would break at a point less than the desired torque. This can happen for 2 reasons. the more obvious one is that there was simply a manufacturing flaw with the bolt and you exceeded its capabilities. The second is not so obvious. The torque and stress that a bolt sees is assumed to be in line with the bolt. If you start applying a force at an angle, you are creating forces that can grow very rapidly inside the bolt, even though the force being applied is very small. An example of this could be turning a bolt with the torque wrench at a 45 degree angle to the bolt, not being at the required 90 degrees (perpendicular) to the bolt. the other possibility would be having a small piece of debris under the head of the bolt causing the bolt to load up on one side and have nothing under the other. This would twist the head sideways, causing the bolt to sheer.

NOw, for the inconsistent feeling in a torque wrench, it could be that the wrench is getting old and is binding up. It is sounding like you were using a clicker style torque wrench. Something that can be done to improve its operation is to set it to the desired torque then to go to a bolt that you can apply atleast this amount of torque (a steel plate with a nut welded to it works well for this). You would then "torque" this nut 3-5 times to exercise the torque wrench at that setting. This will tend to make the torque wrench be a bit more consistent. But, it could have been something as simple as also not having the torque wrench at a 90 degree angle to the bolt. You start getting at funny angles and the applied torque can get all goofey on you. I am sure there are Youtube videos on this. Just don't confuse angular torque with no being on straight to a bolt. Angular torque is something completely different and is used with either torque to yield bolts or achieving seriously high torques (like getting into the millions of ft-lbs, yes I have to deal with torques like that).

NOw for the spring washers that you are talking about, I am assuming you are talking about locking washers. These have a certain amount of "spring" to them. But, this will not affect the torque on the bolt. The locking washer is simply crushing down and the torque on the bolt is still being seen by the bolt and nut.

ONe thing that just popped into my head that can cause things to seem goofey is which side of a bolted connection you use the torque wrench on. The torque wrench should ALWAYS be on the nut of a bolt and nut connection. If you apply the torque to the bolt, there are losses and this can lead to an improper torque on the nut, and therefore, improper clamping forces. I guess I am also missing a big thing in that are you using any lubricants. You may think this is a minor thing, but in the torquing world, lubricants are major players and depending on the lubricant you use can result in the bolt not having sufficient clamping force or breaking before you reach the desired torque. Most bolts on a car are meant to be put together dry (ie, not lubricants). If a lubricant is desired, it will be stated. I have seen wheel studs break because someone got tired of their lugnuts being hard to get off. So, they lubricated them and then torqued their wheel on (well, attempted). Lucky for them, they sheered the bolts off in the driveway. Imagine what would have happened if they torqued them and then hit a pot hole, having all the studs fail at the same time driving down the road.

If you have more questions, please ask. I will explain things as many times as it takes to get the point across. This is something that was life and death to me. When you live on a submarine and you are bolting stuff together that keeps seawater out, you do it wrong, it gets ugly really quickly.

A departing thought, clicker torque wrenches are ok for the backyard mechanic, but they have to be used a certain way. If at all possible, using a bending arm or a dial torque wrench is better. This way, you can see the torque build up and you can feel if you are torquing correctly (ie, you learn to know how much you have to pull to get a certain torque if you are keeping things in line properly).

 

Chris, that is a fabulous reply pitched just about right for my level of experience and knowledge. As you probably guessed I'm no trained mechanic just a home or shade tree mechanic.

I think I understand your points especially about being at right angles to the length of the bolt.

Our sheared bolt was relatively long for us 2 1/2" and passed through a square section frame and a couple of plates attached to the space frame that makes up the engine mounts. These lined up well but not perfectly so we had to belt it through with a nylon hammer. My suspicion is that it was not perfectly perpendicular to the frame and there was sideways stress. Also we were using the (click) wrench on the bolt head not the nut mostly due to ignorance with the excuse of access being tight as well.

Here's a supplemental. We had to use an extension bar in some cases again due to access so I assume this increases the risk of not applying the torque at the right angle?

Also at one stage the only way to get the wrench near a bolt head was to use a 1/2" to 3/8" drive convertor and then a wobble bar to reach the bolt head. The actual socket was perpendicular but the the wobble bar and so the wrench was way off right angles. Would this screw with the delivered torque?

There was me thinking click wrenches were better than the deflector ones. So something like this angular torque (EDIT: no on reflection I have misunderstood this) or this might serve me better? I fancy the dial one as access may be better. I think my Teng click wrench is petty good quality but I'd rather have accurate than a pretty tool.

Also interesting what you say about lug nuts. I always torque mine and always release them after the car has been in the shop as they always use an air gun at max. But I also usually but a small dab of copper grease. Maybe not in the future.

Once again great reply (which I have forwarded to my friend).

 

drmike, the angular torque wrench you show is not something you would normally use. That is mainly only used when doing head bolt torque. But, this is where you are taking the bolt to a yield point which is something that unless you are either following directions very closely or you understand a lot about the joint that you are making up should not be used. Torquing to yield makes for a very strong joint that will not give even a fraction of an inch. But, that there is the problem. You go a smidge too far and you break the bolt. Kinda like if you ever look at a head bolt after you pull it out, there will be a small section of it that is slightly reduced in diameter. You put so much stress on the bolt that it started to stretch like taffy and actually got slightly thinner in that one spot.

Now, the deflector beam wrench (the second one you list) is going to be something that is better to use.

You mentioned that one of the joints was torqued with the torque wrench not perpedicular to the bolt. Yes, this affects the torque on the nut. This is bad for 2 reasons: 1) the torque applied is in 2 directions and one is turning the nut, the second is trying to twist the nut off of bolt sideways (ie, attempting to sheer the bolt). This mixed motions of torque result in the applied torque to the nut being less than what was indicated on the torque wrench. 2) like I eluded to in reason #1, you are twisting the nut in the wrong plane and you are trying to rip it off the bolt which if you are lucky, simply damages the threads. Worst case, sheers the bolt.

Using an extension bar has no impact on the torque applied as long as you are keeping the extension inline with the bolt. You start getting it off at an angle, see what happens in the paragraph above. We have actually played around and had about 8 feet of extensions. The torque was exactly the same as if we had the socket on the end of the torque wrench. Now, keeping all that straight, that was a different story.

The torque wrench on the head of the bolt is not a recommended way. The example that you give is the reason why. Any drag on the bolt is torque that is being eaten up and not applied to the nut. I liken it to welding the head of the bolt to a metal plate then applying a torque wrench to head. You can torque that head to whatever torque you want, but none of it is making it to the nut on the other side of the plate. Now, there are circumstances where some manufacturers weld the nut to a part of the car (done on the X-Type for the rear suspension). In this case, yes, you have to torque via the bolt head. But, this is where you want to make sure that the bolt moves as freely as possible before torquing things down. This way, what you read on the torque wrench is what is applied to the nut.

When talking about lubricating a nut, please keep in mind that there is a right and wrong way to lubricate a nut. I know you are probably shaking your head right about now. I put some grease on the threads and torque it down. I'm good to go. No you are not. Yes, you lubricated the threads (where friction occurs) and you reduced the friction there. But, keep in mind, you have a face of the nut that is coming in contact with another metal surface and that has friction too. So, to not throw off the torque applied, you need to lubricate both the threads and the mating surface of the nut (grease applied to the bolt is lubricating the threads of the nut as long as it is all the way around on the bolt). If you take say a steel bolt into a steel nut, it has a friction coefficient of about 0.6 to 0.8 that is put together with no lubricants. You apply lubricants (assumes something fairly slick), this drops to 0.15. So, if you torque your lugnuts for example with a well lubricated stud/bolt setup, you are going to somewhere between 4 and 5.3 times the recommended torque. Copper grease is similar to what I said with having a friction coefficient of 0.15. Now, you were more than likely not quite as bad as my example because you didn't grease the mating surface of the lugnut. So, probably fair to say that you only went to twice the recommended (not bad really in the big scheme of things, bolts can take a lot of load really).

Remember me talking about the bolt acting like taffy when taking it to yield torque. This is what happens when you normally torque a bolt. The bolt stretches ever so slightly (we are talking 0.002" for every inch of bolt length between unloaded and getting near max allowable torque). When you take off the nut, the bolt relaxes and shrinks back to its normal length. This stretching is what holds the joint together. You want to see this first hand, get yourself say 5 inches of all thread (something just slightly shorter than what your calipers can measure. Stick the all-thread through something and put a nut and washer on each end. Snug up the nuts just enough to hold the all thread in place. measure the length of the all thread. Assuming you are using say 1/2" all thread, take it up to say 75 ft-lbs. Measure it again. I bet you will find that it grew around 0.004" of an inch. Not a lot, but it got longer. Bet you never realized bolts did that. The bolts that hold the reactor vessel head on the reactor on a submarine, when they "loosen" them (they don't remove the nuts, they get pressure welded during the torque process due the extreme torque), they cut the bolt and when it finally releases the torque, the gap in the center is about 0.25". That is how much the bolt is stretched. But, keep in mind that these bolts are 4-5 feet long and torqued to around 3 million foot-lbs. But then, these are torqued by heating the bolt up (causing it to expand), torquing the nut to some ridiculous torque (around 10,000 ft-bls as I recall) and then by knowing how hot the bolt is, they can calculate the final torque, adjusting the hand applied torque value to get the desired torque. This is just some interesting factoid information for you.

 

Thanks again Chris.

I'm making progress but I can do the simple now like we will revisit all the nuts & bolts fitted so far and check the torque with the wrench on the nut. Where the bolt sheared I think we need to make sure the fit is better and the bolt follows a straight path. On the other hand it's not my car so the owner will decide!

 

If ever there were a prime example of why your car should be serviced by a Jaguar dealer (or by the owner if he/she is competent) this is it. What a story!