UPDATE: 316 Stainless for Brake Rotor Mounting?

[jwinwi]

Howdy All,
Apologies if this has been covered before but searching this site yielded no results...
Who has used 316 Stainless Steel Button Head screws for Sport 1100 Front Brake Rotor attachment?
Last time I used 10.9 Black Oxide coated Alloy Steel - of course they rusted.
316 Stainless is rated at 70,000 PSI Tensile Strength; is that strong enough?
Naturally I will use Red Loctite to make sure they stay put.
Thank you in advance to those who have used them on their own bikes 

[dguzzi]

Not button heads but I have used ss allens for brake rotors. I just use blue loctite.  No problems.

[jwinwi]

Can't say for sure where the problem started but after stripping the hex socket out of 2 (!) Stainless button head screws during installation I'm going back to 10.9 Alloy steel with Zinc plating. One came out with a screw extractor... one didn't.

Makes sense to me now that 10.9 might be specified for the durability of the hex, not necessarily for the strength of the threaded portion of the fastener. 

[pyoungbl]

Stainless Steel tends to be brittle compared to steel.

[John A]

Metric stainless is marked different .  It is  marked 50, 70, 80 roughly corresponding to grades 2,5,8. I use stainless with a property class 80 for brake rotors with no troubles.,   I use antiseze not Locktite

[Tusayan]

I’ve replaced the button head brake disc screws with stainless socket head cap screws (SHCS) on several 1100 Sports and Daytonas.  They work well.  Using them means you can torque them properly (unlike the ridiculous button head screws) so they don’t come loose.  Button head screws in this application are really a poor choice, requiring Locktite because you can’t properly tighten them.  The only time they might make sense is when other screw heads hit the speedo drive, as on some Ducatis.  Not an issue on an 1100 Sport with no speedo drive on the front wheel.

Austentic stainless steel (e.g. 316) has very high elongation to failure - it is more like chewing gum than glass, not brittle at all, quite the opposite.  High strength martensitic stainless (e.g, 440C) is brittle, and wouldn’t be used in this application.

When using stainless socket head cap screws to retain brake discs, it’s best to lubricate them to prevent galling and seizure, as mentioned by others. Permanent (red) Locktite would be a compete disaster next time you needed to remove them.

[jwinwi]

Metric stainless is marked different .  It is  marked 50, 70, 80 roughly corresponding to grades 2,5,8. I use stainless with a property class 80 for brake rotors with no troubles.,   I use antiseze not Locktite

The stainless fasteners did not have any markings but I bought them from a trusted Moto Guzzi parts supplier specifically for the brake rotor application. Perhaps they received the wrong grade from their supplier? I used Medium Strength Blue Loctite this time.

[boatdetective]

Stainless Steel tends to be brittle compared to steel.

You have that the other way around. Hardened steel like the 10.9 machine screws here all have brittle cases from the nitride hardening process (over a ductile steel core).  Austenitic stainless steel (the 300 series grades as discussed here) use chromium and nickel to help prevent crevice corrosion and pitting. However, the austenitic grades cannot be hardened, so all behave quite ductile. A process called precipitation hardening was developed to produce grades such as 17-4PH, which can deliver 120-130,000psi. The trade off is that 17-4PH does not have the best corrosion resistance and can be subject to stress corrosion cracking.