Tuesday, December 9, 2014

Grease is noble

Recently, I had occasion to pull bottom brackets out of two different bikes.  Both bottom brackets were Shimano's Hollowtech II external bearing models.  One bike was a custom titanium Seven with full Dura Ace.  The other was a Norco (or was it a Novara?) steel framed touring bike.  The Seven has low miles and is stored in a barn about 1/2 mile from Tomales Bay.  The steel touring bike has seen a lot of miles and a lot of rain, including one 3' deep forging a week ago.  What do you think I found when I pulled each bottom bracket?

Not enough info, right?  Okay, the reason I pulled the bottom bracket in the Seven was because the cranks would barely turn by hand.  Something was binding the bearings.  This is a bike that isn't ridden in the rain.  It's cleaned and wiped down after each ride.  In other words, it's babied a bit.  To remove the cups, a bit of, uh, persuasion was used.  When they finally disengaged, there was a pile of powdered flakes inside the shell - looked a bit like sawdust.

And the cups were slowly being eaten away from the inside out.  The anti-seize looks like it only coated up to the end of the threads, leaving exposed aluminum.

No photo of the seized bearings, but the non-drive side wouldn't turn at all by hand.  

The original bb install was done with the copper based anti-seize.  For every mechanic, there is a different opinion regarding grease vs. anti-seize when installing aluminum parts into titanium frames or titanium fittings into aluminum parts.  If you've been around the work stand since the titanium fastener company SRP was around, you probably reach for the copper anti-seize since a little pack of "Ti Prep" was included with SRP bolt kits.  And then there's simply using grease.  Which one is most appropriate?

To find out which barrier to use, I called both Moots and Seven.  Both simply said "grease."  The guy at Moots did say some of the guys there also like to use the silver colored anti-seize for extreme conditions.  But both had a caveat:  periodic maintenance meaning removal, cleaning, regreasing. 

Back to the Seven.  What the heck happened?  Galvanic corrosion happened.  Galvanic corrosion happens when two metals with numbers on opposite ends of the anodic index interact.  The more noble titanium started a reaction with the lesser noble aluminum.  Check out the chart below.  Oh look, titanium and aluminum are at opposite ends!  And how many aluminum seat posts and bottom brackets are installed in titanium frames?  Yeah, a lot.  So get your non-conductive grease layer between your titanium and aluminum.  I like grease and I use it judiciously on bottom brackets - coating the whole thing and a layer spread inside the bottom bracket shell.  Yeah, it's a bit messy, but it really does protect the internals.  And if dirt and crud get into the frame from the seatpost area, the grease will also capture it.  Doesn't really matter what kind of grease. 

Chart sourced here - a simple search for "galvanic corrosion" will yield plenty of reading material.

Back to that Norco touring bike.  The owner wanted to be proactive and asked me to pull the bottom bracket to make sure it was all okay because he had been riding in the rain and had recently submerged the bb riding through a stream.  If he was doing this kind of riding, my first thought was I would also drill a drain hole in the bb shell.  I pulled the bb and found plenty of grease on the threads, on the plastic center tube, and coating the spindle.  And there was already a drain hole in the bb shell.  Who ever installed the bb for him originally had done a great job.  I told him so and I wish I could remember the name of the shop who installed the bb for him to give them props.

One final thought on that Seven - if that bike had lived the same life in Phoenix, AZ, there would have likely been no problem.  However, since it lives in a barn that is not exactly sealed like your home interior and is near a salt water bay in a high humidity region and the riding it sees is along said bay, the salt in the air is what really acted the part of conductor between the titanium and aluminum and got the corrosion party started. 

"Hi Mrs. Titanium, can Ti come out and play?"
"I'm so sorry, Al, but you know you and Tye don't play well together when you aren't dressed properly.  Why don't you go home and have mum dress you properly, then little Al and little Ti can have a grand time."

(What's playing: New Order Shellshock)


Jason T. Nunemaker said...

Very timely post, as I recently adopted a late model Litespeed (from when Litespeed meant "made from titanium by the Lynskeys in Tennessee") Appalachian and was wondering if I should hunt down anti-seize compound before subjecting it to an Iowa winter. Glad to hear that the combination of good ol' fashioned grease and my usual compulsive tendencies to overhaul will do the trick.

Bod said...

Huh, exactly the same thing happening on my Ti bike, nibbles on the inside of the Shimano bearing cup. Didn't happen with the King BB that replaced it though for some reason.
Nice little project to get me away from the in-laws over xmas...

Anonymous said...

Mike, What happened to the Ti bottom bracket shell? Were you able to restore it back to original condition or was it trashed?

blackmountaincycles said...

Joe, Nothing happened to the ti shell. The corrosion happens to the element that is least noble (in this case, aluminum) on the anodic scale.

Anonymous said...

I like to use Sta-Lube Marine grease or boat bearing grease.Its nice and thick and water rolls right off of the stuff.With Titanium Bottom Bracket Shell sometimes I mix the silver in color anti-sieze with grease.Works well on Bottom bracket cup threads and Titanium shells.

Ric said...

After "vast" experience in bike maintenance in the soggy Pacific NW, I can attest to the excellence of Sta-Lube; too thick for bearing grease, but for threads, and seat posts, it is the cheese. Inexpensive, as well.