[Closed] Engineering question - bolt torque

[i] molgrips - Member

I could put the cat among the pigeons by calling myself an engineer..... let's see how that goes[/i]
This is STW, where anything can happen. Just don't take it seriously. Oh!, hang on!

[i]It really pisses me off how people say 'take it to a garage'.. ok .. you gonna pay for that? Do you think I'd be farting about with it on the driveway if I had the cash to pay someone else? Let me remind you that all this shit started when I took it to a bloody garage. [/i]

Further consideration makes me question your assumption that any independent VAG specialist you might have taken your car to, wouldn't have seen this issue before. Indeed, there could very well be said independents for whom this repair is familiar and a regular service they might provide at nominal cost and far less stress to the owner.
🙂

[i]Just not a very good one judging by your initial quesion[/i]
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[quote=gonefishin ]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.

So why the requirement to replace after 5 uses, when any of that could have happened at any time after the first installation?

Though of course if its your car and you know what work's been done on it, you know whether it's been nipped up or not, and your suggestion that recording and documenting the torque makes a difference smacks of the whole ISO9000 documentation improving quality shenanigans.

[i]So why the requirement to replace after 5 uses, when any of that could have happened at any time after the first installation?[/i]

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Solo, you may well be the greatest most knowledgeable engineer the world had ever known, but almost every post you've made on this thread has been condescending, argumentative or just plain trollish. I fail to see how someone wanting to save money or further their knowledge merits such derision and smug gittishness from yourself.

<mod>
If you want to help and answer questions, do so. If you don't, don't. But kindly desist from constantly making little digs to try and get a rise out of someone or make them look foolish, otherwise I shall be forced to remove you from the discussion.
</mod>

Dear Moderator.

You have mail.

Here's some references to stainless bolts, in case you use them instead of the steel grades

Please don't use stainless steel in this application, it will be carbon steel for a reason. You might get away with stainless but it's not uncommon for stainless steel bolts to cause more problems than they solve due to their susceptibility to chloride stress corrosion cracking.

You have mail.

Oh good.

This thread has got too long for me read fully but there is some good info in there.
The bolt science website is a good reference.

To work out the max torque the following equation can be used.

Torque(N.m) = K(factor based on head and thread friction for a lubricated bolt)x diameter(m)xBolt force

The numbers used here are only for a 8.8 steel bolt assuming an equiavlent strength hole.

at75% of yield strength bolt force = 640MPa x 14.2mm^2 (tensile area) x 0.75 =6816N

Therefore Torque = 0.18*6816N*0.005m=6.1Nm.

If the bolt material is different or if the hole material is weaker than the bolt then the torque needs to be adjusted.

It is always best to work to manufacturers torque. Can you not try and get a Haynes manual for the car, which should list the torque values?

haynes..... have a torque value ......for more than the wheel nut in a modern car

BAAHAAHAAAHA and even then it would likely be wrong :d

Aracer - there are many bolts on a car known as Stretch bolts.

they have to yield slightly to do their job properly.

most of these can be identified by torque rating + n degrees - headbolts , steering bolts , some suspension bolts.

[i]Please don't use stainless steel in this application, it will be carbon steel for a reason. You might get away with stainless but it's not uncommon for stainless steel bolts to cause more problems than they solve due to their susceptibility to chloride stress corrosion cracking.[/i]

When I suggested using a new bolt, I had intended that the OP would obtain one from VAG, irrespective of this particular repair.
Doing so would take care of the question of material. I wouldn't suggest the OP goes and uses just a new bolt, even if there is a material choice available. One reason being Auto OEMs are either compelled or choose to use fixings which may have coatings applied to them in some cases.

The minefield grows larger. If a new bolt/s can be obtained from VAG as a fixing for any number of uses on the gearbox. Then I'd consider replacement for new. If a bolt can't be obtained from VAG, then the decision is made for the OP. He'll re-use the bolt/s they have.

[i]Oh good. [/i]
😆

Here comes the hammer!

OP - Have you tried sourcing any VW forums for advice on this? I know the T4 forum has lots of useful information on it for example.

It might make more sense to ask about car repairs on a car forum than a bike one

I'd never have got such detailed information on a car forum, trust me 🙂

Just not a very good one judging by your initial quesion

I'm a great engineer. Just not a mechanical one 🙂

Indeed, there could very well be said independents for whom this repair is familiar

Hahaha.. lol 🙂 Trust me, I have done a LOT of research on this.

[quote=trail_rat ]Aracer - there are many bolts on a car known as Stretch bolts.
they have to yield slightly to do their job properly.
most of these can be identified by torque rating + n degrees - headbolts , steering bolts , some suspension bolts.

Yep, I'm aware of those, though don't think I've ever removed one, and should have clarified that we weren't discussing those - I'm fairly sure none of the bolts mentioned fall into that category (molly's valve retention bolt certainly doesn't). Of course you also don't use those 5 times before replacing!

[quote=Solo ]When I suggested using a new bolt, I had intended that the OP would obtain one from VAG, irrespective of this particular repair.

Though as discussed, it's almost certain that he won't be able to get a replacement from VAG, as it's not officially a serviceable unit. Do you reckon a VAG bolt for a similar purpose (if such a thing exists) would be OK then? Otherwise it seems you do actually agree with me that there's nothing much wrong with reusing the existing bolt.

[i]Hahaha.. lol Trust me, I have done a LOT of research on this. [/i]
I don't doubt that, you've already explained you've more time than cash. I haven't questioned your resolve, but exploding at the suggestion of taking the car to the garage didn't help.

However, if we might be permitted to sensibly discuss this, I would suggest that your research has lead you to a few conclusions, [b]which seem[/b] to coincide with internet use, only.
Failure to find a torque spec online, doesn't mean it isn't published, While not finding that torque is decidedly inconvenient (I sympathize), those in the know, here, have pointed out that production lines building said G/Bs will use driving devices with pre-set torque values, so the data is somewhere. It's just that google may not be able to help.

If you could have discerned the G/B supplier (is the supplier company name on the G/B) then e-mailing them might have provided you with the torque value you need. What have you to lose?

Anyway, have you reattached the valve assembly to the gearbox now? I assume this is an insitu task?

This is to fix the fault with the vag gearboxes yes mol?
I was aware of the Swedish fella but hadnt looked further. Start to finish if you had all the parts you needed how long a job?

[i] Do you reckon a VAG bolt for a similar purpose (if such a thing exists) would be OK then? [/i]
Yes, for the reasons I have already stated in conjunction with the fact that OEMs prefer to use common fixings as much as possible, esp wrt the constraints which may be imposed during the main assembly process, including number of tools available at that station and costs of using an excessive number of uncommon fixings, for purchase and tooling reasons.

[i]Otherwise it seems you do actually agree with me that there's nothing much wrong with reusing the existing bolt. [/i]

No, I do not agree with you. If it's wrong, you have a secondary problem, "nothing much" doesn't come into it when you are relying on stuff to work within spec to perform a certain task.
The risk of breaking down because hydraulic fluid has leaked out of the G/B for lack of achieving the correct clamping force between the valve assembly housing and whatever it fixes to, is not one I would willing face for lack of trying to source and use a new bolt and by doing so massively increasing the chances of a completely successful valve replacement. This is the basis of my recommendation.
Ultimately there is too little known about this repair/valve replacement, so excising logical, sensible, hopefully inexpensive practices such as using a new bolt, shouldn't be dismissed, imo.

Are there any markings on the head of the bolt?

Presumably the bloke supplying the valve doesn't suggest a torque?

I'll get my coat

[quote=Solo ]Ultimately there is too little known about this repair/valve replacement, so excising logical, sensible, hopefully inexpensive practices such as using a new bolt, shouldn't be dismissed, imo.

Except we were talking about the scenario in which he can't get an exact replacement (almost certain) and that VAG can't supply a similar one (which seems likely, as it's seems it's not something they assemble themselves). Given that it's not a stretch bolt, and that it will have only been previously assembled once to a specified torque which won't have resulted in plastic deformation (the likelihood of somebody having "nipped it up" on a non-serviceable unit is negligible) there will be no difference between the removed bolt and a brand new one - it's actually preferable to using a new replacement which may not be exactly the same.

[i]Except we were talking about the scenario in which he can't get an exact replacement ([b]almost certain[/b]) and that VAG can't supply a similar one (which [b]seems likely[/b], as it's seems it's not something they assemble themselves). [/i]
[i]Given that it's not a stretch bolt, and that it will have only been previously assembled once to a specified torque which won't have resulted in plastic deformation (the [b]likelihood[/b] of somebody having "nipped it up" on a non-serviceable unit is [b]negligible[/b]) there will be no difference between the removed bolt and a brand new one - it's actually preferable to using a new replacement which may not be exactly the same. [/i]

You're repeating your point, and I don't think anyone is suggesting the OP use a non identical bolt. However, you appear to be ignoring my explanation. So seeing as you won't take the advice of someone in the "know" and seeing as you appear to need to demonstrate that you know more about the industry I work in, than I do. There's nothing more I can do for you. You simply won't be told. If this was your task, I'd happily go along with you using the original bolt, if for no other reason than to have you stop hassling me. It's tiresome.

Cougar.
YGM.

Edit:
[i] ampthill - Member
Presumably the bloke supplying the valve doesn't suggest a torque?
I'll get my coat [/i]
Not at all, it was a good suggestion.
🙂

Haven't you been struck with the ban hammer yet?

I decided on page one to just nip it up. I do not believe it is in any way critical.

Start to finish if you had all the parts you needed how long a job?

You will need:

New front cover seal
New front cover bolts (as rec. by VW)
5l new dsg oil
New dsg oil filter

Drain oil
Remove front cover. Directions suggest removing the side cover too but I have no idea why.
Unplug g509 sensor
Undo 10 hard to access bolts
Pull mechatronic unit out, whilst thrutching and swearing
Almost drop it on your face because it is much heavier than you think
Change clothes due to getting covered in oil when you thought it was empty
Clean driveway for same reason
Take unit into kitchen in a foil disposable roasting tin
Undo 2 bolts to remove valve, refit new one. Takes 1min.
Repeat for second valve.
Refit is the reverse of removal except there is a set sequence to redo the bolts
Refill oil due via one of several techniques widely documented online. Takes anything between 10 and 45 mins

I am going to try it with the unit in situ as I think it should work and save time. Total time would be probably 4-5 hours for a home bodger I reckon. But you have saved a packet on your next dsg fluid change.

[i] molgrips - Member

I decided to just nip it up[/i]

The Stabilizer Wins! yay 🙂

Op.... The torque man, the torque! What torque did you settle on?

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