[Closed] B/b threads destroyed in Ti frame - why?

Grit in the BB either during building or down the seat tube working it's way into threads? It's an odd one but I'd still use coppergrease myself and try a new bb. Might be just a fluke.

I have a Ti frame which destroyed a Campag Record BB in much the same way. I assume that there's a galvanic reaction between the aluminium and Ti.

Reaction of metal on metal?

I'm sure I've read previously that there can be reactions between Ti and other metals.

X-post

PTFE tape around the D/S BB thread helps to preclude creaks and will protect both threads.

Have you used the bike in winter on the road?
This will destroy the aluminium and the proximity of Ti will accelerate it. Ti has excellent resistance to salt water corrosion. It also possible the thread was damaged when installed allowing salt water in.

I'm not sure but I think copper grease is better in this case than Shimano grease (for a titanium frame) as it is designed to conduct (so short-circuit an electrolytic reaction) rather than insulate.

It's possible that if you only applied copper grease to the BB (and not the shell) then when you screwed in the BB, all the grease worked its way down the threads to the "outboard" end, which left the "inboard" end un-greased and caused the reaction. If so, apply plenty of grease all the way down the threads in the shell as well as to the BB threads.

: P

Not sure how kosher a fix this is but I've always used PTFE tape rather than copper grease on my Ti frame. This is mainly because its the only way to stop a creak but if your problem is due to a glavanic reaction it should cure that to.

http://www.stainless-steel-world.net/titanium/ShowPage.aspx?pageID=173

There you go in laymans terms. The big bold bit at the bottom and 3 😉

Since an electrolytic reaction requires conductance, you're right. You weren't sure.
😉

Thanks scienceofficer 🙂 - my A-level chemistry was a long time ago! I vaguely remembered something to do with two different metals in solution, but that's not the same reaction as two different metals in contact (galvanic?) or two different metals well-insulated from each other (a non-reaction!)

: P

http://www.stainless-steel-world.net/titanium/ShowPage.aspx?pageID=173

Galling.
Use Loctite 222 or Molyslip molybdenum disulphide.

Loctite 222
thread lock / thread seal acts as a lube, sealant and anti-sieze.

Rocol Dry Moly Spray is like a paint and can help prevent galling.

http://www.finishing.com/Library/titanium.html
"With specifics to titanium, its corrosion resistance is compromised by exposure to halides such as chlorides or fluorides. Residual chlorides lead to stress corrosion cracking while fluorides readily attack the natural oxide that protects titanium from atmospheric corrosion. In addition, due to titanium’s extremely passive nature, when titanium components are in contact with more electrochemically active materials such as aluminum, zinc or copper, where the materials meet there is such a galvanic charge generated due to the dissimilar metal junction, galvanic corrosion is wildly accelerated beyond what either metal by itself would experience.

Another shortcoming and that most often associated with titanium is galling. When titanium slides against titanium it tends to gall or stick more so than any other metal combination. Similarly, titanium to titanium parts in threaded combination “cold weld” making disassembly impossible without destroying the parts. In order to prevent this, typically dry film lubricants are applied over suitably prepared titanium (i.e. either anodized or conversion coated)."
Galling can happen with aluminium or titanium (also with stainless steel).

http://www.timet.com/cor-p05.htm
crevice corrosion
"The limiting factor for application of titanium and its alloys to aqueous chloride environments appears to be crevice corrosion. When crevices are present, unalloyed titanium will sometimes corrode under conditions not predicted by general corrosion rates (See Crevice Corrosion). TIMET studies have shown that pH and temperature are important variables with regard to crevice corrosion in brines."