Torque wrench settings

[Rob Y]

I was looking in the blue workshop manual to check some torque settings and they all show a range of settings from x to y. For example cylinder head attachment 60 to 80 lbf.ft (8.3 to 11.1 kgf.m). can someone please explain this to me? Sorry if it's obvious. what should I set my torque wrench to?

 

cheers

 

Rob

[Guest ntc]

Rob

Start at 60 then 80

[Fireman049]

I've always torqued my cylinder head starting with a low setting and gradually building up to the maximum recommended settings. This way, the head studs take the tension gradually.

I don't think it's ever wise to go to maximum straightaway.

 

Hope this helps.

 

Tom.

Edited November 28, 2014 by Fireman049

[Rob Y]

Thanks, I hadn't thought of that. I wasn't actually planning on taking the head of at this stage - although I might do at some point in the not too distant future. I did on my old Spitfire but that was some time ago and I cant remember how I did it. I was just curious about the 2 figures - it states it for every setting - there are always 2 numbers. Is it common practice then where the torque setting is important that this is done in 2 stages?

 

Cheers

 

Rob

[Motorsport Mickey]

Hi Rob,

 

Mechanical sympathy, as Tom says it's unwise to take a torque up to its final figure (unless a wussy one like 5-7 lb ft) in one go.

The cylinder head even being a good few inches thick will distort as the torque is applied, if you had a surform reading or spectrogram analysis the higher torque and therefore stress areas would light up red, therefore better to stagger the torque application certainly into 2 or as I do 3 separate settings to the max shown. Too much in one area in a single torque can cause the head to squirm (microscopically you understand) and shuffle the head gasket.

 

Also when you are winding the torque onto the wrench if you go too far do NOT just wind the torque setting back to your required number. There will be small discrepancies in the thread form and I was always taught to wind the setting back at least 20 lb ft below the required number and then again approach it in one smooth twist so as to help eliminate any backlash and inaccuracies caused by it.

 

Mick Richards

[Fireman049]

Mick is quite correct. When I torque up cylinder heads I usually do it in five increments.

This gives the head studs time to adjust to the tension. I remember one chap who torqued up his cylinder head

in one go and snapped one head stud!

 

Tom.

[john.r.davies]

Got to agree, that's what I do, but not to spare the studs. Tension in those must be instant, or Young's modulus is Old and Creaky's modulus, and I think that Tom's friend's stud would have gone anyway. It must have been weakened already.

 

Instead, and as Mickey says, the mechanical sympathy lies in not tightening head studs to the full amount while others are still loose - that will stretch and distort the head in unpredictable ways. Go around the head in the prescribed order, taking them all up to progressively higher tightness until you achieve the figure you want. At least two or three rotations usually.

 

But the range of torques prescribed. Is that to cater for the inevitable variation in torque wrench accuracy? I BROKE a block this year, putting in head studs! It split at the front-right, where the meat of the block is thin. When I discovered that my wrench was under reading by 30%, the cause was obvious. In future, I'll calibrate my wrench before a major job!

 

JOhn

[Dave Smith]

John - May I ask how do you calibrate your torque wrench?

 

As already said its very important to keep all the bolts to similar torque, so when loosening I go around the cycle many times.

Same on tightening I start with a spanner get them all just tightening and progressively go around the cycle many times with spanner at first then torque wrench. I tighten to the lower or just over and go about mid range at 500 miles, that way if the wrench is slightly inaccurate it should be close to the range given.

Edited November 28, 2014 by Dave Smith

[Motorsport Mickey]

Dave,

 

If your torque wrench is inaccurate check it's calibration, don't risk it.

 

Normally relief torque wrenches (those that click or release the torque when achieved) are at their most accurate at about the mid point of their spread range ie wrench with a 40 lb ft to 120 lb ft spread is most accurate at about 80lb ft range.

 

You can buy an Acratork gauge to check torque wrenches from e bay or other sources used, prices vary depending upon the range they cover by model L1. L2 etc my L3 model covers up to 0-400lb ft which I reckon does me for any automotive requirements needed, larger numeric models will need a scaffold pole to input the torque required to check ! They are self calibrated operating by function similar to a torsion beam bar (like the torque wrenches used by the men in brown coats who made our TRs originally) deep behind their clock faces. They are extremely robust and are probably proof to all abuse other than being run over or set on fire !

 

If I was working in a BAE or Rolls Royce environment I'd be bothered enough to cross check the calibration every year, but in a home use garage I reckon checking the gauge against a newly purchased torque wrench (I normally buy after about 3 years) which is sold calibrated does the job, so far wrenches and Acratork agree within couple of pound.

I bought my Acratork from Anchor Supplies in Nottingham who dispose of ex WD equipment for £30 along with a couple of single set fully weatherproofed wrenches at £10 each adjustable by screwing a tensioning screw. Useful when racing to have set at wheel torques etc without having to check or reset.

 

Failing this more technical approach place a nut and bolt through a piece of timber and place in your workshop vice. Weigh how much the torque wrench is and place the torque wrench via a socket onto the nut adjusting it so it is horozontal. Allowing for the weight of the wrench hang weights at a 1 foot range from the centre point of the bolt to suit your checking range (I'd suggest at least 40 lb) and wind the calibration scale upwards stopping frequently as you approach the selected setting, in this case 40 lbs at 1 foot.

If all is accurate the wrench should click off when it meets the 40 lb ft setting confirming that your wrench inclusive weight of 40 lb at a 1 foot range is correct.

 

Mick Richards

Edited November 28, 2014 by Motorsport Mickey

[Motorsport Mickey]

Here's pictures of Acratork

 

and single set weatherproofed torque wrench,

Edited July 8, 2015 by Motorsport Mickey

[john.r.davies]

Thank you, Mickey, for that description of DiY torque wrench calibration, which is how I do it.

But I don't make up a block with a nut'n'bolt in it, I just clamp the drive shaft in a vice, so that the wrench pivots vertically.

I think it's reliable and can prove it.

This chart shows my over-reading wrench. The black line is the settings, the purple the point at which it clicked, when moving a heavy weight outwards. I use old flywheels, 9-12kgs.

Grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr!

Bloody Windows 8.

I can't paste the picture here.

Suffice that the variation from a straight line of the response is less than 2%.

 

John

 

 

 

[Motorsport Mickey]

John,

 

I quite agree about Windows 8, even Steven Hawkins said " it does my bloody head in" and that's good enough for me.

 

I'm slowly working through the fixes to try and get 8 to work properly with copy/paste and picture transference, I can't even get it to print it refuses to send the data to printer, it's messing with the wrong guy here, I'm relentless.

 

Mick Richards

[ptjs1]

About 6 months ago, I messed up my old 1/2" drive Torque Wrench when I foolishly used it in conjunction with a piece of scaffold tube to undo a VERY tight wheel nut on a friends car.

Since then I can only use it as an unlocking ratchet and can't use it as a torque wrench to tighten.

So, I've been looking around to purchase a new one and toying between buying an electronic one as opposed to a £25 OK-ish quality screw type.

Browsing on the internet, I saw an interesting alternative from Machine Mart which is an electronic torque 1/2" adapter enabling one to use any ratchet or breaker bar. I'm not usually a huge fan of Clarke tools although they do have a big reasonably-priced range and their Pro range does have a lifetime guarantee. So I thought this might be an interesting alternative enabling me to use my existing 1/2" & 3/8" (with an adapter) drive ratchets.

It has a very good range of 22 lb ft to 265 lb ft (I have a small 3/8" drive torque wrench which does lower figures), reads the exact torque clockwise or ant-clockwise and can be programmed to sound a buzzer when you get close to your set torque figure. A few quick tests indicated that all the wheel nuts on one wheel of my XJS all loosened off at a figure within 4 lb ft of each other which seems quite remarkable considering I did them up originally by hand without a torque wrench!



The adapter came in a good quality storage box and a certificate of calibration which seems to indicate a high degree of accuracy.



Early days but at £35 I'm really quite pleased with this so far.

 

One of the advantages of this electronic device is that you can easily use it to check the consistency of other torque wrenches just by connecting them together. I checked an old 3/8" drive wrench which was almost exactly spot-on, and then checked a colleagues 1/2" drive wrench which proved to be almost 25% out. That was quite a shock to him!

Paul