Bloody Disc Bolts

[Fosse Foxfight]

Anybody managed to find any decent replacement disc bolts ie stainless or other suitable non ferrous, for front and rear discs? Typical Ducati have used a shallow socket head, which is basically bad design as they dont like torquing up. Ideas?

Sean :mad:

[Pedro]

I think Billy Big Wheels has stainless bolts from Spareshack. Whatever, if you do use Stainless, make sure they are A4 grade at least - much stronger.

ProBolts & Aerotek do Titanium if your fleeing rich

Ped

[Chris]

I've changed mine for Titanium which are nice but £60 ish for a set

[Fosse Foxfight]

Hmmmmm, actually Pedro A4 for disc bolts wouldnt be the best. A4 is 316 and as such is harder, not neccessarily stronger. In hindsight using stainless for disc bolts isnt such a brilliant idea. A better material would most likely be 304 (A2). Basically stainless just isnt a good tensile material, and I think Im gonna hold back and go for the titanium. Not that I want to shell out the 50 odd quid that it costs, its just I hate ferrous metals and corrosion :(
Anyway did you get those footrest bolts made Pedro?...did ya huh, did ya? :burnout:

Sean

[Pedro]

Hmmmmm, actually Pedro A4 for disc bolts wouldnt be the best. A4 is 316 and as such is harder, not neccessarily stronger. In hindsight using stainless for disc bolts isnt such a brilliant idea. A better material would most likely be 304 (A2). Basically stainless just isnt a good tensile material, and I think Im gonna hold back and go for the titanium. Not that I want to shell out the 50 odd quid that it costs, its just I hate ferrous metals and corrosion :(
Anyway did you get those footrest bolts made Pedro?...did ya huh, did ya? :burnout:

Sean

You're probably right about the disc bolts which is why I've not changed!

No, I haven't had the hanger bolts made yet! To busy! Thought I might get the originals stripped and chromed instead.

Ref the Titanium bolts - check out your local fastener companies rather than Probolt etc. Usually much cheaper and a superior grade

Ped

[M900Dom]

NEVER use stainless bolts for Brake discs, stainless into aluminium is bad enough for corrosion.
Add Heat cycles and a corrosive element (Salt) and they WILL FAIL catasrophically, the bolt will shear from the root of the thread.
A4 is much more likely to do this, A2 is slightly better but still not suitable.
The same goes for Caliper MTG Bolts, Dont do it !!!

I can do it on the AP Racing Calipers because the Calipers have steel thread inserts, so its Steel on Steel.
If you want pretty bolts then you have to use new Ducati ones at about £12 a set, or Titanium as Chris has done.

Please dont F*ck about with brakes if you dont know what youre doing, you will get hurt.
While we are on the subject, for road use you should never use Aluminium Banjos/Bolts on brake systems either.
A very similar thing happens, they fail without warning, due to corrosion

Sorry for the Rant, but people Die because of this stuff, The internerd is a great place for information, but the danger is if you dont know, how do you know the information you are getting is correct? not just read somewhere else and reposted in the belief it is true ?
Not getting at anyone at all, just concerned for others saftey

FWIW I am a time served, and degree qualified engineer/ Race Engineer, who designs High performance engines for a living, so I do know a little bit about these things.

There are many other on here as knowledgable, Lee (Superlight3), AK, Proto, Moby and probably many more

So please if you are not sure on a saftey related Item, Please ask for Confirmation, from someone who will know, at least if they dont, they will be able to point you to someone who does.....

Cheers
Dom

[Pedro]

Dom

well said & thanks!!

Ped

[Fosse Foxfight]

Dom said "NEVER use stainless bolts for Brake discs"

Dom, in some respects you are on the right track but maybe some slightly flawed logic here and a lack of the full facts.

There is a spectrum of galvanism between "more noble cathodic materials" and "less noble anodic materials.

Corrosion is an electrochemical process involving the flow of electric current, corrosion can be generated by a galvanic effect which arises from the contact of dissimilar metals in an electrolyte (an electrolyte is an electrically conductive liquid). Three conditions are required for galvanic corrosion to proceed; the two metals must be widely separated on the galvanic series as mentioned, they must be in electrical contact and their surfaces must be bridged by an electrically conducting fluid. Removal of any of these three conditions will prevent galvanic corrosion.
So in order to mitigate this effect between alu and ss the use of a copper grease will reduce the electrical contact, not allow the ingress or an electrical conducting fluid and therefore the removal of the last and the reduction of the other will mitigate the dissimilarity of the materials.
So QED, galvanic corrosion is not a problem if the appropriate precautions are taken.


Dom said "I can do it on the AP Racing Calipers because the Calipers have steel thread inserts, so its Steel on Steel."

When I build a machine I automatically check all threads in any non ferrous materials and all of my disc bolts are going into helicoiled inserts anyway.

Dom said "If you want pretty bolts then you have to use new Ducati ones at about £12 a set, or Titanium as Chris has done."

Big mistake Dom, as Titanium is even more prone to galvanic problems than stainless steels as it is more cathodic.

(Sorry but as the forum allows 4000 charcacters Ive split the rest into a new post)

[Fosse Foxfight]

Dom said "Please dont F*ck about with brakes if you dont know what youre doing, you will get hurt."

I do know what Im doing thank you Dom :) Probably more than most.



Dom said "FWIW I am a time served, and degree qualified engineer/ Race Engineer, who designs High performance engines for a living, so I do know a little bit about these things."

Ditto in addition to a great deal of experience with Materials Science and applications of materials in extreme conditions.

It is worth noting that disc bolts themselves carry out a limited task. The bolts act as a means of closing the gap bewteen the disc face and the mounting face of the wheel. The majority of the work of the discs in terms of braking is carried out on this frictional joint and little stress is transferred to the bolt. This is evidenced by the fact that most motorcycle manufacturers will bolt discs directly onto threads that are tapped into aluminium, without the use of thread inserts. It is perhaps more germaine to recommend to anybody who is replacing their disc bolts that they observe a strict regime when replacing the bolts with regard to correct tightening and torquing. From the top of my head I think the disc bolts are torqued to 28 Nm? This is a low value and relates to the fact that the aluminium threads in the wheel will not take anymore than maybe a 5% error, before stripping.
I hate threads in aluminium, period, and as a matter of course I always helicoil threads in aluminium as I feel more comfortable with this.

So there you go Dom......apologies if the original question was asked in a flippant fashion but maybe in future when I ask a question I shall qualify it and disclaim it. I see where your coming from, but as you can see, because your reply contained some inexactitudes I felt it neccessary to fill in the grey areas, hope you dont mind.

In conclusion, I wold advise that anybody who is electing to "pretty" up their disc bolts as Dom puts it, should first remove the wheels, remove the discs, examine the threads for ANY signs of tearing, run a plug tap thru to clean out the hole, and no matter what the material you choose for your bolts apply a generous portion of a good quality copper grease, and if it was me then I would routinely have the threads "helicoiled" to provide total piece of mind. Upon assembly tighten the bolts in 2 stages say 20 then 28 Nm and if you havent helicoiled your aluminium threads and your torque wrench, which should be well looked after and calibrated, does not indicate a stop at this value then, you should disassemble and have thread inserts fitted.

Reckon that just abouts covers everything eh matey? ;)

Oh and dont forget, if you do use titanium its more prone to galvanic corrosion than stainless (304, 316, A4, A2, 18/8 whatever notation you use) and the above steps to mitigate this should be well observed.

OK now stand back and let someone start the tensile strength debate...hehehehe....dont do it Dom :p

Hope this helps

Sean

[Fosse Foxfight]

Oooops should have said that Titanium will cause a worse galvanic situation than stainless as of course the least resistant material will suffer the most, ie the aluminium side......just thought Id better make that clear..ahem :o

Sean

[M900Dom]

And bow to your superior knowledge ;)
Thanks for clearing it up :D
I shall go and read up on Materials

I still dont trust Stainless Disc bolts, so In answer to your original question , you might want to check out ARP, they do all sorts of Specialist Fasteners, we mainly use them for Con rod and Main bearing Bolts.

Cheers
Dom

[crust]

mmm, ok

so folks, advice is use copaslip to bridge the galvanic divide.

Now, simple explanation please.

Fosse, you say use copper grease, torque to specified torque, in this case 28mn.

You also state that aluminium threads are not very strong - you say 5%

How does the presence of grease affect the torque figure? Is there a percentage allowance? or is it minimal, ignore it and use the factory figure?

Am interested in this as there's a lot of bull surrounding this. Have been told that grease will lower the correct torque figure.

:) Crust

p.s guys, thanks for the technical stuff.

[steviej]

mmm, ok

so folks, advice is use copaslip to bridge the galvanic divide.

Now, simple explanation please.

Fosse, you say use copper grease, torque to specified torque, in this case 28mn.

You also state that aluminium threads are not very strong - you say 5%

How does the presence of grease affect the torque figure? Is there a percentage allowance? or is it minimal, ignore it and use the factory figure?

Am interested in this as there's a lot of bull surrounding this. Have been told that grease will lower the correct torque figure.

:) Crust

p.s guys, thanks for the technical stuff.



it doesn't affect the torque, it places a barrier between the male/female components of the joint................. :)

[M900Dom]

it doesn't affect the torque, it places a barrier between the male/female components of the joint................. :)

Any lubricant (Like coppaslip) will affect the torque required, as will Loctite.

20 Nm Dry is far less torque at the threads than 20 nm oiled/greased, due to the reduced friction under the head of the bolt, and on the threads.
Its a case of RTFM ;) :D

[steviej]

:confused: :confused: :confused: :confused:

[Dave Pearson]

When I used to have time to get my hands dirty with this kind of thing, I seem to remember that the most accurate and reliable way of tightening nuts/bolts was based on degrees not torque.
This was due to the differing amounts of friction found on threads due to lubrication/wear etc.

I've probably still got my degree attachment for a 1/2" drive socket somewhere....

Is this practice still used, or has the theory/practice been discredited?

Just interested....

Dave

[crust]

Any lubricant (Like coppaslip) will affect the torque required, as will Loctite.

20 Nm Dry is far less torque at the threads than 20 nm oiled/greased, due to the reduced friction under the head of the bolt, and on the threads.
Its a case of RTFM ;) :D

RTFM :rolleyes:

carefull, cos one of their chappies is on here but Hay......I mean some manuals dont mention this in relation to torque figures.

Is there a rough percentage figure to reduce the torque figures by, or is it a piece of string type question?

Its my enduro/MX background that says cover every thread in copaslip/grease :twisted:

:) Crust

I just know its one of those engineers palm tickling things that mere mortals arent allowed to know

[Fosse Foxfight]

[QUOTE=M900Dom]And bow to your superior knowledge ;)
Thanks for clearing it up :D
I shall go and read up on Materials

B*ll*cks Dom, I aint havin no bowing round here :o Get up, get up, ya see thats what bloody academic environments do to you, I had to get all bloody Orange Boxy, when all you were doing was sending a friendly warning.
OK, ok enough already.

I still dont trust Stainless Disc bolts, so In answer to your original question , you might want to check out ARP, they do all sorts of Specialist Fasteners, we mainly use them for Con rod and Main bearing Bolts.

Hmmm, in truth, I havent used stainless there yet, mainly cause Ive not found one with a suitable head length and to be honest the socket heads that Ducati have fitted as standard arent ideal as shallow sockets are a bitch to torque reliably, Ill check out this ARP, cheers Dom :cool:

ta ra for now.