My crank recently became stiff to turn on my cross bike (only 10 mo old). I took it apart and found about a teaspoon of really fine sand/dirt inside. After cleaning and lubing it's back to it's normal self. But I'm left with a head-scratcher - how did it get in there?
Granted we've had some huge gully washers here in Denver lately, and I've gone through some deep mud and sand next to the creeks on my commute. Thinking that the dirt and grit may have gotten in the seat post and fell down the seat tube, but no, it's not open. I can't find any openings on the frame (Motobecane Fantom Pro Cross). Could that amount of dirt gone through the clearance between the crank and bearings? Seems unlikely to me. Any ideas where I can look for the answer anyone?
Related question - how often do y'all tear down and clean the bottom brackets when you're riding in dirt and mud occasionally?
Sand has a remarkable ability to get into places it shouldn't. There are vent holes in your chainstays near the dropouts and an opening in the BB shell where the chainstays mate to it. Any water/sand that gets into the chainstays through the vent holes will wash down to the BB shell.
However the FSA MegaEXO BB uses sealed cartridge bearings. So even with sand in the BB shell, it should be somewhat difficult for it to get in and gum up the actual bearings. I did 10 Florida CX races (lots of sand) last season on an FCXPro and when I pulled the BB at the end of the season, there was sand on the surface of everything, but nothing inside the bearings themselves.
Thanks for the input everyone, I'll check out the areas you mentioned and see what I can find. Now I'm starting to question if I'm hitting it too hard with water and getting water into the bearings. I use a "gentle sprayer" on the hose end, but maybe that's too much pressure... Anyone know if getting water in there requires a tear-down, or will it eventually dry itself out and return to normal?
Redline Conquest Pro, Kona Cinder Cone, Trek Fuel EX8, Nashbar tandem
Drain holes in the BB shell help. After our first season of cyclocross in Portland I found mud inside the BB shells of the 2 Redline bikes without drain holes and no mud in the BB shell of the Focus bike with a large drain hole in the BB shell.
I will add that the stock FSA Mega Exo bearings aren't that well sealed so after a season of CX they were crunchy and I swapped them out for Enduro bearings which have held up much better.