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Max bolt torques, but what about nuts?


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Not TR related, but hoping to tap into the well of knowledge on this forum.

Fitted Reich motor movers to the caravan yesterday, and diligently tightened bolts up using torgue wrench to the setting given in the instructions of 60NM, this on a 10mm bolt and nut, needless to say one of them has stripped and now cannot be unscrewed..

I have just looked up the torque settings for a 10mm 8.8 steel bolt and have come up with 2 different answers of 45 and 55 NM.  Both being less than the manufacturers reccomendation.   A 10.9 grade bolt can be taken to 75 NM, but the supplied bolts are 8.8.

I will now have to remove the adjacent bolts and nuts so that I can get the angle grinder in and cut the offending item off, and given that all eight (4 on each side) have been overtightened I will have to replace the lot which is annoying.

If I buy 10.9 grade bolts, do I also need to buy a similar grade nut ?.  I don`t yet know whether it is the bolt thread or the nut thread which has stripped .

Ralph

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Ralph,

From Engineering Toolbox website
Size(mm)    Typical Maximum Tightening Torque (Nm) 
                                       
Grade 8.8    Grade 9.8    Grade 10.9    Grade 12.9
M5    7.0    7.8    10.0    11.7
M6    11.8    13.3    17.0    19.9
M8    28.8    32.3    41.3    48.3
M10    57.3    64.1    81.8    95.7
M12    99.8    112    143    167
M16    248    277    354    413
M20    500        690    809
M24    865        1195    1395
M30    1719        2377    2774

Sorry about the poor tabulation, but that quotes lesser values than you found.

I'd go back to the shop and complain!

John

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52 minutes ago, Ralph Whitaker said:

If I buy 10.9 grade bolts, do I also need to buy a similar grade nut ?

Of course you must.

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Hi Ralph,

 the Nut AND Bolt would be subject to the same forces. So, the nut needs the same rating as the bolt.

I had the same problem with EBC vented discs. I had to fit a spacer in the caliper and one of the supplied bolts stretched like liquorice.

Upon asking they simply said then use a lower torque !!!!:blink:

 

Roger

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I suppose the motor mover came with the nuts and bolts supplied, that's how they would come normally, ...in which case I should check the calibration of your torque wrench ! A supplier who specs up materials less than the required torque spec is not long for this world.

Undo and remove some of the easier to get to nuts and remove the bolts and inspect and see if signs of damage are apparent before going "Tonto" on it. Can you maybe get a nut splitter onto the failed nut and then wind it off without having to grind off ?

Mick Richards

 

Edited by Motorsport Mickey
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4 hours ago, RogerH said:

Hi Ralph,

 the Nut AND Bolt would be subject to the same forces. So, the nut needs the same rating as the bolt.

I had the same problem with EBC vented discs. I had to fit a spacer in the caliper and one of the supplied bolts stretched like liquorice.

Upon asking they simply said then use a lower torque !!!!:blink:

 

Roger

Roger,

Having watched a caliper on pressure test split when the thread of the bolt failed, I would think long and hard about which bolts I used to assemble the caliper and spacer.
 The test/failure was done to demonstrate incorrect bolt type fitment in safety critical items like motor vehicle calipers.  The pressure used was not in excess of possible working or emergency use pedal pressure.

 

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Ralph,

all of the above.

This is not a critical application, so if the supplier provided 8.8 bolts, I would use these. The correct nuts should be stamped “8”, if tgey are not stamped you do not know what they are.

Although 10.9 bolts would not be wrong, they are more brittle and more expensive, so I would stick with whatever the vendor specifies.

50 Nm would be correct for un-lubricated bolts/nuts. If you use Mo2S (the grey colored grease), 20% less is required, so 40 Nm. 
This will give a tensile stress of approx. 90% of the (guaranteed) yield stress, so don’t go beyond those values. In other words: if you apply 20% more torque (which you did), you could have over-stessed the bolts. In practice, it depends on how much margin the is in the bolt material. Good quality bolts will often have much higher actual yield stresses is my experience (compared to the minimum required values per the code (weather ASME or DIN).

Just in case you wonder:
The accuracy of hand-torqueing (with a simple torque wrench) shows a large spread in achieved bolt stress, which is no problem in most cases, certainly not here, it is not rocket/science.

Waldi

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The question of the torque wrench's accuracy, mentioned above, may be critical.   I once ruined an engine block by torquing in the studs (I know now, you don't!) And cracking the block!    Testing later found the wrench was under readng by 30%!

Testing on the bench is straightforward.   Clamp the drive bar, the square that fits in the socket, into the vice so that the handle is horizontal.   Hang a weight on the handle and move it outwards until it clicks.  Then weight divided by the distance to the drive bar is the torque exerted, in whatever units you like 

John

Edited by john.r.davies
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And for the purists:  take the weight of the wrench times COG into the equation, for better accuracy. 

Waldi

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On 4/17/2022 at 9:58 AM, john.r.davies said:

Ralph,

From Engineering Toolbox website
Size(mm)    Typical Maximum Tightening Torque (Nm) 
                                       
Grade 8.8    Grade 9.8    Grade 10.9    Grade 12.9
M5    7.0    7.8    10.0    11.7
M6    11.8    13.3    17.0    19.9
M8    28.8    32.3    41.3    48.3
M10    57.3    64.1    81.8    95.7
M12    99.8    112    143    167
M16    248    277    354    413
M20    500        690    809
M24    865        1195    1395
M30    1719        2377    2774

Sorry about the poor tabulation, but that quotes lesser values than you found.

I'd go back to the shop and complain!

John

Don't forget that the maximum tightening torque depends on several factors; the material, the friction on the threads and the friction under the head. For applications where the clamping force applied by the bolt is critical e.g. cylinder heads, the thread should be lubricated. I can hear you saying "what about threads that need to be locked?". In these cases, the threadlock provides some lubrication before it sets.

This seems counter intuitive but the torque needs to go into exerting a clamping force rather than into a high friction thread.

Tom

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1 hour ago, Tom B said:

Don't forget that the maximum tightening torque depends on several factors; the material, the friction on the threads and the friction under the head. For applications where the clamping force applied by the bolt is critical e.g. cylinder heads, the thread should be lubricated. I can hear you saying "what about threads that need to be locked?". In these cases, the threadlock provides some lubrication before it sets.

This seems counter intuitive but the torque needs to go into exerting a clamping force rather than into a high friction thread.

Tom

Tom,

I hope we now don't have a clump of unknowing owners lubricating cylinder head studs and nuts and happily turning 105 lb ft on them !

As stated many times before on this forum the Triumph torque numbers  are all to be fitted DRY...no lube. It's not stated in the workshop manual, but I  I once asked Dave Gleed (recently passed Triumph competitions mechanic) about the torque figures in the Triumph manuals on whether they were “dry” or lubricated…that got a withering look ! “Nope, dry as a vicars toast” he said ( apparently they make do with tea), “ideas about lubricating threads had never made it to the Triumph engineers of the time”.

Although these days it's well known that a lubricated thread will achieve more reliable and repeatable torqueing numbers, the lubricating of fastenings on the engine especially the cylinder head nuts where "big numbers" are used will risk stripped nuts or studs in the block, the materials used are right on the limit. The removal of "stiction" (sticking friction) from the fastenings by lubrication will INCREASE the actual poundage applied through the threads by about 20% and so a maximum of 90 lb ft torque will achieve approx 108 lb ft actual clamping force (against 105 lb ft shown in the manual) depending upon the lubricity of oil or grease being used. A 105 lb ft applied torque if lubricated will deliver about 126 lb ft ! ...a very dangerous area of force, risking block damage. If using ARP fastenings where lubrication is stated and their special lube mix is supplied I've use the 90 lb ft as specified, the fastenings are very nice and torque up smoothly.,   

On standard OEM studs and nuts (Triumph fastenings are very high quality) the threads should all be cleaned of all residual oils and gasket materials (sometimes Well seal or other sealing materials finds it's way onto thread surfaces). I use a small container of thinners and after dipping, soaking and wire brushing clean, minutely inspect the thread surface of all nuts and studs using a magnifier and follow it up by turning a scriber point down all the threads to help find any "galling" (thread pulling or damage to the thread surface). Any fastening that shows signs of damage or necking (only 2 studs in 23 engine rebuilds) are discarded and replaced from my spares bins. Afterwards I spray with WD40 (because it cleans and displaces moisture but has only a minimal lubrication affect) and then wiped dry before being used in a rebuild, I budget 2 hours for fastening preparation.  

Mick Richards         

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On 4/22/2022 at 10:03 PM, Motorsport Mickey said:

Tom,

I hope we now don't have a clump of unknowing owners lubricating cylinder head studs and nuts and happily turning 105 lb ft on them !

As stated many times before on this forum the Triumph torque numbers  are all to be fitted DRY...no lube. It's not stated in the workshop manual, but I  I once asked Dave Gleed (recently passed Triumph competitions mechanic) about the torque figures in the Triumph manuals on whether they were “dry” or lubricated…that got a withering look ! “Nope, dry as a vicars toast” he said ( apparently they make do with tea), “ideas about lubricating threads had never made it to the Triumph engineers of the time”.

Although these days it's well known that a lubricated thread will achieve more reliable and repeatable torqueing numbers, the lubricating of fastenings on the engine especially the cylinder head nuts where "big numbers" are used will risk stripped nuts or studs in the block, the materials used are right on the limit. The removal of "stiction" (sticking friction) from the fastenings by lubrication will INCREASE the actual poundage applied through the threads by about 20% and so a maximum of 90 lb ft torque will achieve approx 108 lb ft actual clamping force (against 105 lb ft shown in the manual) depending upon the lubricity of oil or grease being used. A 105 lb ft applied torque if lubricated will deliver about 126 lb ft ! ...a very dangerous area of force, risking block damage. If using ARP fastenings where lubrication is stated and their special lube mix is supplied I've use the 90 lb ft as specified, the fastenings are very nice and torque up smoothly.,   

On standard OEM studs and nuts (Triumph fastenings are very high quality) the threads should all be cleaned of all residual oils and gasket materials (sometimes Well seal or other sealing materials finds it's way onto thread surfaces). I use a small container of thinners and after dipping, soaking and wire brushing clean, minutely inspect the thread surface of all nuts and studs using a magnifier and follow it up by turning a scriber point down all the threads to help find any "galling" (thread pulling or damage to the thread surface). Any fastening that shows signs of damage or necking (only 2 studs in 23 engine rebuilds) are discarded and replaced from my spares bins. Afterwards I spray with WD40 (because it cleans and displaces moisture but has only a minimal lubrication affect) and then wiped dry before being used in a rebuild, I budget 2 hours for fastening preparation.  

Mick Richards         

Mick, Slight mix of units: the clamping force will be lbf (pounds force) but I get the drift. Note that the figures in my manual for TR6 are much lower than stated. The critical figure here is the stress in the bolt compared to the UTS of the material. Strange advice though - I have done may cylinder heads on different cars and the advice is always to lubricate the threads. When the car is serviced, and the cylinder head torque is checked, they will have been well lubricated in any case ........

All the best

Tom

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Where does it say in any car's service schedule that the cylinder head nut torque should be checked?

Yes, 200-500 miles after rebuilding, but not for service in  use.

John

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11 minutes ago, john.r.davies said:

Where does it say in any car's service schedule that the cylinder head nut torque should be checked?

Yes, 200-500 miles after rebuilding, but not for service in  use.

John

Big Brown Book (TR6) p26 item 19 after 1000 miles - which, by that time, all will be well oiled.

Regards

Tom

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Yeah, that's the original retorque normally carried out by the factory, these days because of the usage cycle of these "trophy" cars we tend to short circuit the retorque mileage otherwise the car might be another 12 months before it gets to 1000 miles use !

Also if we are using in competition we don't have the time, so 200 miles is fine for annealing whatever metals in the engine need it carried out in one afternoon, and after the engines been allowed to cool and reheat a few times it's then retorqued.

I'm not sure about engines which are "well oiled" by use on the threads though, whether 4 or 6 cylinder, I'd revisit your quality build process, mine are nice and dry.

Mick Richards 

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Tom,

That's not an in-service service, that's the initial post-build service.    If your head nuts loosen after that something is wrong!    As it is if the threads get oiled in use.

Apart from the above, there is no need to re-torque head nuts, ever.   Suspension bolts are a different fish of kettles.

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I don’t understand how the studs on the LHS of the engine won’t get oiled. They are inside the rocker cover and will be splash lubed by the oil emerging from the holes in the top of the rockers. 

Rgds Ian

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1 hour ago, Ian Vincent said:

I don’t understand how the studs on the LHS of the engine won’t get oiled. They are inside the rocker cover and will be splash lubed by the oil emerging from the holes in the top of the rockers. 

Rgds Ian

Agreed, but those nuts are already tightened and when undone are again cleaned and dried, these cylinder studs with a coil of lead linger around the head face stud surface which gets trapped and spread under torque load (it doesn't interfere with the torque loadings) prevents any oil seepage down into the block stud threads, and any water seepage UP the stud in the event of a minor leak, so they are dry.

Micky

Edited by Motorsport Mickey
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On 4/25/2022 at 7:45 PM, Motorsport Mickey said:

Agreed, but those nuts are already tightened and when undone are again cleaned and dried, these cylinder studs with a coil of lead linger around the head face stud surface which gets trapped and spread under torque load (it doesn't interfere with the torque loadings) prevents any oil seepage down into the block stud threads, and any water seepage UP the stud in the event of a minor leak, so they are dry.

Micky

What`s this about lingering lead?

Ralph.

PS, going back to the original post, I regularly check my torque wrench with a spring balance. There is a setting mark on the handle at exactly 12 inches from the centre of the 1/2" drive square. I grip the square in the vice with the handle horizontal so that the weight of the handle does not affect the readings, and then pull the handle with the spring balance, checking at 30, 40, and 50 ft lbs. I checked it again after stripping the bolt and according to my balance it was clicking at 3lb under. Of course my spring balance could be faulty I suppose, but you have to have some faith in your equipment.

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Hi Ralph,

'lead linger' is a thread like material somewhat like thin gauge solder but without the flux.

It is gently wound around the base of the stud and when the washer and nut squeeze down it makes a good fluid seal.

 

Roger

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29 minutes ago, RogerH said:

Hi Ralph,

'lead linger' is a thread like material somewhat like thin gauge solder but without the flux.

It is gently wound around the base of the stud and when the washer and nut squeeze down it makes a good fluid seal.

 

Roger

Especially used on the oil pressure adjusting screw on 4 cylinder oil filter heads.

Stuart.

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1 hour ago, Ralph Whitaker said:

What`s this about lingering lead?

Ralph.

PS, going back to the original post, I regularly check my torque wrench with a spring balance. There is a setting mark on the handle at exactly 12 inches from the centre of the 1/2" drive square. I grip the square in the vice with the handle horizontal so that the weight of the handle does not affect the readings, and then pull the handle with the spring balance, checking at 30, 40, and 50 ft lbs. I checked it again after stripping the bolt and according to my balance it was clicking at 3lb under. Of course my spring balance could be faulty I suppose, but you have to have some faith in your equipment.

Ralph,

Rather than a spring balance to check the wrench, why not use a actual mass?   Sure, you need to measure the mass weight using another fallible machine, but once done, maybe checked on several scales, you know what it weighs, and can use it again.  I have an old flywheel, over 20lbs, that I hang on my torque wrench to check it.  That mass won't change!

John

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John,

I think Ralph is implying that you grip the wrench in the vice so that you pull it horizontally with the spring balance, so the weight of the handle does not upset the reading. (As Waldi mentioned.)

However I think your method of using weights  (and pulling down) is easier as at least, as you say, you can you can use a variety of scales to verify the weight.

You could be lucky and find an old set of butcher’s weights and then there would be no need to weigh them. Although such items are now considered “Objet d’art” to sit on kitchen shelves in places like Shoreditch and so command silly money.

Charlie.

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I didn't understand Ralph's "grip the square in the vice with the handle horizontal so that the weight of the handle does not affect the readings,"  unless 'horizontal'  meant "vertical"!   In which case, a spring balance would be necessary to exert a measured torque on the wrench.   But IMHO the weight of the handle is  trivial.

John

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