Stainless steel front disc Allen bolts?
 

Anyone fitted them?

I have a set ready to fit, but haven't put them on yet.

I should say, I am aware of two things: the possible danger of "cathodic" corrosion from dissimilar metals (largely overcome by the application of Copaslip, IMO), and, secondly, the fact that stainless steel is less strong than the steel that bolts (and especially allen screws) are normally made from.
(Contrary to that, I'm also aware that in some circumstances, the plating process on "ordinary" steel bolts can do damage which can seriously reduce the strength of the fasteners. This *ought* not to happen, if the correct de-embrittlement processes are carried out...)

I am a design engineer by trade, and had actually wondered about doing a basic fatigue analysis. Only thing I'd need to know is the actual braking force (in kg or whatever). If anyone has any data on this, I'd be grateful to hear it.

My gut feeling, however, is that whatever shear stress is induced in the bolts by the the couple of the braking effect, it is fairly small and nowhere near the yield stress of even 316 stainless.

So has anyone fitted stainless bolts here, or have any other useful data/comments? I'd be interested to hear.


[edit]
I'd also add that I'd guess that the full strength of the stock fasteners (Grade 12.9?) would be unlikely to be fully utilised, becasue the tapping in the hub would probably fail before the screws did.

[Edited on 26-2-2005 by moto748]

You said it yourself "and, secondly, the fact that stainless steel is less strong than the steel that bolts (and especially allen screws) are normally made from"

Titanium works thou:D;)

I have used these sorts of bolts before. No sweat. But........... be very careful when you are removing them. As you have said, the material is not a tough, and I have found that the hex bits tend to ovalise (new, made up word) the broached hex in the screw/bolt.

Rgds, Rob

I have used both "normal" allen headed stanless bolts and torx type.I have only ever had problems with the allen type:

1:You can't torque them up properly 'cos the key normally starts to round out the socket
2:They are an absolute bitch to get back out.I had to use a chisel/punch/hammer/impact driver to get my twelve out.

When i used the torx ones,no probs at all torquing them up and absolutely no problem taking them out.I would advise against using the normal ones.

Give Nelly a shout,he has them.

Shazaam has spoken..........

http://217.199.188.40/xmb/viewthread...=9368#pid76885

and

http://217.199.188.40/xmb/viewthread...=7427#pid60474

I have S/S button head cap screws fitted to the front discs of my 998s without any problems and have also fitted them to my Jota without any problems!

are they torqued up and have you had to remove them yet?:(

Even the std ones I've just removed were a nightmare.

Sprayed with release fluid overnight.
One Allen key socket snapped.
Sadly ended up hammering an old Torq socket into the screws and using an impact driver finally got them out!!!

Even though everything would warm up together is there any mileage in bringing a wheel / item into the warm for a while I wonder?

Frank

Well as I said in my first post, I'm aware of the cathodic/galvanic whatever-you-want-to-call-it issue, but I've I've been putting stainless steel allen screws on my bikes since Triumph Bonneville primary chaincases in the Seventies, and can't say I've had too many problems with that.

Funny to see titanium mentioned. Titianium of course comes in various grades, but my understanding was that titanium bolts are around the same strength as stainless ones, and certainly not up to Grade 12.9 standards. If anyone has chapter and verse to show me different, I'd be interested to see.

Personally I can't say I've had any issues with ovalling of the recesses. of course, with stainless, as with titanium, there are better, and less good suppliers around.
I'm not at home to check the torque setting of the bolts in my manual (and does ducati.com even give this sort of info any more? It used to have torque settings and all sorts of useful data available when the 748/998 bikes were current), but as they're a tapping, rather than "nut and bolt", I'd be surprised if they're that high.


Jasper> What material are the torx screws you mention made of?

The Torx are stainless.

Thanks, Jasper.

Here 's a pic.

Stainless are fine if you use decent ones, I've had them in the ST2 for ages, the standard ones fitted aren't very high quality, certainly not on a par with Unbrako or similar Hight Tensile screws. Shear forces are not hight enough to cause any problems. Not seen any evidence of corrosion due to dissimilar metals. I've put a lot of stainless bolts on the ST2 as it does see some use in bad weather.

I've never bothered to calculate the shear forces but if the brakes exerted enough force to cause the bolts any grief the front wheel would constantly be locking up wouldn't it :D:D

I did my disc bolts at the weekend as I need to fit two disks instead of the original single disk on the 600ss DD bike.

The Haynes BoL says 26Nm for the disk bolts - which I thought was quite low but it did pull up quite tight and I did get the odd one start to "ovalise".

If you use normal cap heads, make sure the heads clear the speedo drive. They usually hit it a fraction hence using button heads is preferable.
As mentioned above, the buttons come with a hex size lower than the cap head and can give problems tightening/undoing them.
Torx is the way to go ;)

I've used stainless for years on all sorts of bikes without problems.

I managed to get some with shorter hex heads, which only just clip the speedo drive. Luckily it's only made of plastic so a quick trim of it with a Stanley knife means it's fine :D

I have always been under the impression that decent stainless steel has a higher tensile stree value than normal steel, so if the bolts are of the same value they will be strong enough.
shazaam's post puts it all dead straight re torque values and lubing of threads, and I see no reason for the heads to be chewing up if the tools used are of good quality. If the head can't resist 30Nm of torque loading should you really be trusting it with your main brakes?

As a point of interest, carbon is the highest member of the galvanic table. How many of us have insulated our frames, forks, swingarms etc from the carbon parts fitted?

Out of interest, I have been told that if the depth of engaged thread is more than 2.5 times the bolt dia. (and the threads are in good condition), the bolt will snap before the threads strip in the alloy. I also think that the disc bolts are in tension and not in shear, the braking forces are transferred due to the clamping force between the disc and the wheel.

Iv'e been asked this before and sent this_

normal Zinc plated bolts have a tensile strength of 500 Newtons/mm2
stainless steel basically starts at 500 N/mm2 for class 50 up to 800 N/mm2 for class 80.
High tensile bolts are about 800 N/mm2 - usually stamped 8.8 on the head.
So if you want to be really sure about the strength get some stainless steel grade A4 class 80. Alloy fasteners have a huge range due to the various metals available, but are unlikely to be over class 80 on a bike.

also you have to be carefull about putting stainless bolts into alloy as disimilar metals react with each other causing corrosion, this can be prevented using copaslip or similar - there was a post about this very recently - you then have to reduce the tightening torque to copensate for the lubricate tread - to about 60% of the stated torque.

Sorry, but this simply isn't true.


There are pistons both sides of the disc in the caliper, don't forget!

The point I was trying to make is that the braking force in the disc is transmitted to the wheel hub by the friction between the disc and the hub and not by driving on the bolts so they should not be in shear (unless they have slackened and the clamping force between the disc and wheel has dropped). Dont think opposing pistons affect this:puzzled::puzzled::puzzled:

Yes, apologies, I slightly misread your earlier post.

I think I'm still right, though! :)

The friction between the disc and the hub you speak of, this itself is generated by the clamping effect of the screws, I agree. But by that argument, you could say that "all" bolts are tension, rather than shear. Structurally, bolts like this are normally designed in shear, according to all the design codes I know, with the exception of certain particular High Strength Friction Grip type bolts with oversize hexagon heads to generate the assumed design clamping force. Cap head allen screws would certainly not normally be designed by the "clamping " method.




But hey, this all getting a bit too much like work!

I'm supposed to be on my lunch-break!:)

[Edited on 18-3-2005 by moto748]