Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > General Motorcycles only > Stainless steel front disc Allen bolts?

[moto748]

Thanks, Jasper.

[Jasper]

Here 's a pic.

[Paul James]

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

[antonye]

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".

[nelly]

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.

[antonye]

Originally posted by nelly
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.

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

[desmojen]

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?

[ducv2]

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.

[Steve M]

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.

[moto748]

Originally posted by ducv2
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.

Sorry, but this simply isn't true.


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