Engineering question – bolt torque

Yes, of course it does – but it’s not published,
[molgripsmode]
I think you know that you really shouldn’t claim that the torque value isn’t published
[/molgripsmode]

Why do you have to turn every thread into a shit slinging fest?
Not at all, I made the perfectly sensible suggestion of taking your car to the garage. Where the staff there would have likely fitted your valve/s for you, if you had turned up with the valve/s in your pocket and your car.
However, after my sensible suggest of going to the garage, you went into orbit. You might do well to try the decaf mate.

Is this really a difficult concept?

Apparently so…..

Not at all, I made the perfectly sensible suggestion of taking your car to the garage. Where the staff there would have likely fitted your valve/s for you, if you had turned up with the valve/s in your pocket and your car.

I would suspect that a VW dealer would probably refuse if it’s not a standard procedure as they’d be worried about warranty etc.

Did you miss the bit about it not being a recommended repair procedure and the torque value not being published? So he takes it to a VAG dealer, they’ll refuse to do that repair. He takes it to a VAG specialist, they might refuse, but most likely will do the repair without knowing any more about the torque value than he does, or indeed doing the job any better as they have no additional information about it. He takes it to a non-specialist they’ll do nothing different to him, but it will cost him more money. It’s not really all that sensible suggestion in the circumstances is it?

I’m not sure what the big problem is with fixing stuff yourself. Even most parts of modern cars (or other consumer stuff) aren’t all that complicated or difficult, and if you have time to spend and can get the parts you can generally fix stuff where a garage would just replace whole units. I’ve also repaired dishwashers, washing machines and kettles, spending far less money than calling in a “professional” every time I have a problem.

I’m not holding my breath
Perhaps some more decaf and you could try not touching your keyboard for an hour.
No charge!
🙂

I would suspect that a VW dealer would probably refuse if it’s not a standard procedure as they’d be worried about warranty etc.
Yeah, I noticed that franchised dealers weren’t going to assist, I own VAG stuff too and it’s a PITA, but ho-hey.
Hence my initial referral to an independent VAG specialist.

I reckon the Stabilizer’s suggestion is the best bet in the absence of an OEM supplier torque spec.

I’m not sure what the big problem is with fixing stuff yourself. Even most parts of modern cars (or other consumer stuff) aren’t all that complicated or difficult, and if you have time to spend and can get the parts you can generally fix stuff where a garage would just replace whole units.
You’ve made an assumption, which is incorrect. But please don’t let that stop you from ranting, some more, if you really need to.

Edit:
If the OP believes it’s critical to achieve good clamping force for the duration of subsequent ownership, I’d suggest a new bolt, if they can be sourced as single items/in small numbers.

Go on, enlighten me, which of my many assumptions is incorrect?

Serious question (not having a go) how would that make a difference?

have you asked the danish connection?

Have you tried taking it to your local garage?

Even most parts of modern cars (or other consumer stuff) aren’t all that complicated or difficult, and if you have time to spend and can get the parts you can generally fix stuff where a garage would just replace whole units.

Yep, and this is a good example. There’s something like 6 or 8 valves on this thing and most of them can actually be re-ground at no cost. It’s only the main clutch valves that can’t. So in many cases the dealers (and most indies – there are only a few who will recon the mechatronics) will bin a £1500 part for the sake of what is really a couple of hours of work.

Some stuff is a lot more repairable than garages would have you believe. They won’t do some jobs because it’s not worth their time financially and carries too great a risk that it won’t work and the customer will start complaining.

have you asked the danish connection?

Best post of the thread – no I haven’t 🙂

Serious question (not having a go) how would that make a difference?
You’ve ranted at me for several posts and now you want to chat?

OP.
I’d of gone in cautiously at 8 to 10Nm (although allegedly I don’t fix or advocate anyone else fixing stuff, etc) , so the suggestion by The Stabilizer sounds sensible to me. Again, if your budget will stretch to it, use a new bolt. I strongly suggest you do NOT lube the thread.
At this time I can’t think of anymore advice to offer. Good luck.

buy these – £1.70!!!!

Spring washers are shite.

I think your over thinking, stick new bolt in and tighten.If you are really worried keep a couple of spares and check the tightness every so often.

I waded in when you posted http://singletrackworld.com/forum/topic/engineering-question-bolt-torque#post-6710229 – you then continued in the same vein. Now you’re the one refusing to be civil because I challenged you?

You could always explain which of my assumptions is incorrect if you’d prefer to continue fighting.

You could always explain which of my assumptions is incorrect if you’d prefer to continue fighting.
You have deliberately missed my first contribution to this thread which allows you to overlook the OP disproportionate response towards me.
And now you’re resorting to baiting, which is against the forum rules.
Do you really need another love letter from the Mods?
I’ll leave you now to bicker with some other poor forum member, you big hitter you.

I think your over thinking, stick new bolt in and tighten.If you are really worried keep a couple of spares and check the tightness every so often.

Not really – I asked if you could work out the torque like that – answer’s no – fair enough 🙂

New Bolt.
Renault suggest a set of standard toques where none are given. Standard torques for an M5 bolt with a 0.8 pitch thread are:

4.8 = 3.2 Nm
5.8 = 4.0 Nm
8.8 = 6.1 Nm
10.9 = 8.9 Nm
12.9 = 10.4 Nm

And you’ll need a good one of these:

And some of this:

Job done.

Can somebody else explain why to me if Solo’s going to flounce? I promise I won’t bite (much).

Marko – Member

New Bolt.
Renault suggest a set of standard toques where none are given. Standard torques for an M5 bolt with a 0.8 pitch thread are:

4.8 = 3.2 Nm
5.8 = 4.0 Nm
8.8 = 6.1 Nm
10.9 = 8.9 Nm
12.9 = 10.4 Nm

Ta daaaaa!

The subject of tightening torques can be a bit of a minefield; it always elicits a groan when bought up at work.
Here’s some references to stainless bolts, in case you use them instead of the steel grades Marko has referenced above. A2-70 is probably the most commonly found stainless fastener:

http://www.grampianfasteners.com/Files/TechnicalCorner/Stainless_Steel_-_Torque_Guidelines_A2_&_A4_-_Grampian_Fasteners.pdf

http://www.fastenal.com/content/feds/pdf/Torque%20of%20Metric%20Stainless%20Steel.pdf

(geek alert)

http://www.tribology-abc.com/sub9.htm

Can somebody else explain why to me if Solo’s going to flounce? I promise I won’t bite (much)

Why not? It will cost pennies and you have no idea if it gone beyond it’s elastic limit when Mr Muppet installed it in the first place. Also VAG and others tend to say if a torque figure and an angle are given as part of the tightening procedure then the bolt must always be replaced.

As a further aside the steering wheel bolt on a 9N VW Polo is 50Nm, but VW say you can only reuse it 5 times. It must then be replaced.

If in doubt always replace the bolt is a good rule of thumb.

And all you will ever need to know is here:

Bolt Science[/url]

Hth
Marko

Fairy nuff. It makes sense in practice from the POV of not knowing the history, though I’m not convinced that it’s good practice to take a bolt near its elastic limit, so in theory it shouldn’t be required. I’m certainly less than convinced by any rule of thumb which suggests replacing after a number of installations – it won’t fatigue over 5, and I can’t see what other mechanisms might be involved.

Am i the only person who never uses a torque wrench.must have done up thousands of nuts and bolts and only remember stripping 2 small nuts on a bike when i was about 12years old. Now i have said this i have to go a buy a torque wrench as i have inevitably jinxed myself. 🙂

aracer -Member
Fairy nuff
😆

A simple formula for calculating the torque for a bolt is T =P*D/5000 where D is major diameter (5 in this case) and P is the bolt pre load. The constant 5000 assumes an friction under the head and thread of 0.2 and a conversion from Nmm to Nm. This is based on a BS spec, don’t have it to hand so can’t quote which one.
The bolt pre load is calculated from the effective tensile area of the bolt multiplied by the lesser of half the ultimate tensile stress or 3/4 yield stress of the bolt material.
NASA also have plenty of available reports on torque tightening of bolts eg http://www.esmats.eu/amspapers/pastpapers/pdfs/2014/hemminger.pdf

When I started reading this thread I had a feeling that knowing it was an M5 must be a handy hint. Looking at dubsapies post some one must know the max torque for your bolt based on its material, thread and diameter. The only other thing to check is the material it’s threaded into in case that’s the limiting factor. Again surely there must tables of Max torques for common metric threads into different material (and presumably the length of the contract)

In a world with no friction and un glued bolt or nut would simply spin off before your eyes

Another general rule used thread engagement is; for a normal strength bolt (A2-70 and the like) then 2*D engagement is required for cast aluminium alloy (UTS ~270MPa) wrought aluminium alloy 1.5*D engagement and steel 1*D engagement. High strength bolts need to be assessed against the female thread shear capacity as stripping the thread can occur before full pre load is achieved. Some thread forms such as spiralock recommend higher torques than normal to lock the bolt.

The bolt pre load is calculated from the effective tensile area of the bolt multiplied by the lesser of half the ultimate tensile stress or 3/4 yield stress of the bolt material.

Err.. yeah, ok boss… I’ll umm.. get right on with calculating that.. 😉

Gotta love STW! Whatever you ask, there’ll be an expert. All interesting stuff.

I’m certainly less than convinced by any rule of thumb which suggests replacing after a number of installations – it won’t fatigue over 5, and I can’t see what other mechanisms might be involved.

Not a ‘rule of thumb’ it’s what VW insist on. You’re meant to put a centre punch mark on the bolt head every time it’s removed and refitted. A few other vehicle manufacturers adopt a similar idea. Ford (if I remember correctly) only let you use the steering column pinch bolt three times.

It is a little odd as both are safety critical items, so why not just say ‘replace it or you or your customer might die’.
Hth
Marko

I recommend you Get one of these!

They are free and dead handy, tightening torques depend on a lot of factors IME, Bolt material and finish, lubrication (or lack there of), desired preload, but it at least gives you guidelines rather than berating you for daring to even wield tools.

That is awesome ^^^

Yep, I just spotted their wall chart myself so I’ll request myself one of those…

Looking at section 1 the guidline torques:

M5:
Gr8.8 = 6.031Nm
Gr10.9 = 8.483Nm
Gr12.9 = 10.200Nm

so it gives Marginally lower values than dunsapie, but TBH I doubt you are actually measuring torque to one decimal place, let alone three…

The table states it’s based on a Frictional value of 0.14 and a preload of 75% of “proof value” (I’d take that as equivalent the 3/4 of Yield stress that dunsapie mentioned)…

So you have a couple of broadly correlating sources…

molgrips – Member

That is awesome ^^^

Yes, Engineering, often over looked and usually under valued. Yet when needed, so apparently indispensable.
A bit more respect for Engineers, anyone?
😉

Which doesn’t make it not a rule of thumb. Totally illogical, as if a single use doesn’t result in any plastic deformation and so require replacement, then it will last 100s or 1000s of installations.

Totally illogical, as if a single use doesn’t result in any plastic deformation and so require replacement, then it will last 100s or 1000s of installations

… and you guarantee that how exactly? The quickest, simplest, cheapest and most effective way is to simply replace the bolt which seem to me to be totally logical.

Calm down Solo.

Don’t get me wrong, I’d love it if engineering was a better recognised and respected profession in the UK, but we’re hardly downtrodden, we’re certainly not infallible, and talking down to/belittling those without the job title who still want to apply some technical aptitude seldom wins the profession any fans.

Personally I applaud anyone who has the gumption to pick up a spanner rather than dial a technician and just throw money at them…

I don’t know how you got started but personally a willingness to take things apart, investigate, and try to repair them was what started me off towards engineering.

In which case you replace it every installation – I don’t have a problem with that. Though if you’ve fitted it correctly using the correct torque, then that provides the guarantee that you have no plastic deformation.

I’m wondering if Solo has me and molgrips in the “doesn’t respect engineers” category? 🙄

I could put the cat among the pigeons by calling myself an engineer….. let’s see how that goes 🙂

*imagines aracer’s name entered on a whole other wallchart*

cookeaa – Member

Calm down Solo.

Don’t get me wrong, I’d love it if engineering was a better recognised and respected profession in the UK,
Is totally calm, but you knew that, once you spotted the smiley ^^^, here:
😉

Personally I applaud anyone who has the gumption to pick up a spanner rather than dial a technician and just throw money at them…
I think there’s a half-way-house, provided said spanner owner then doesn’t proceed to bicker with folk who’s field of expertise is relevant and who may be willing to offer useful advice.

Which leads us neatly to, STW forum dreadlord: arcer!
In which case you replace it every installation – I don’t have a problem with that. Though if you’ve fitted it correctly using the correct torque, then that provides the guarantee that you have no plastic deformation.
Who’s up for educating Arcer? He seems to want to become a mechanical Engineer.

Though if you’ve fitted it correctly using the correct torque, then that provides the guarantee that you have no plastic deformation

I’m afraid it doesn’t. You’d have to use some sort of device to record and docoument you torque had been used. You’d have to put some sort of tell tail on the bolt to make sure no one “nipped it up” some time later. You’d have to do all sorts of other things that are frankly so far over the top that no engineer would consider practicable when you can, for pennies, just replace the bolt.

I could put the cat among the pigeons by calling myself an engineer….. let’s see how that goes

Just not a very good one judging by your initial quesion 😉