Rust inside
Photo of the Ball Bearing (BB) shell attached.
How it started: left crank arm kept working loose. Rare at first, then every few rides, then it came off the spindle. I think the arm was never fully seated on the splines. Chainline measured somewhere around 56mm rather than the 52mm I'd expect, and there's a spacer on the drive side that as far as I understand shouldn't be there on a 73mm shell. My guess is that pushed everything right and left too little spindle sticking out on the left.
So I pulled the BB to take the spacer out. Seemed like a simple fix.
What I found instead: drive side cup was seized, non drive side came out easily. No grease visible on either. Shell interior is rusty, and there are two chipped looking spots in the drive side threads, maybe 5mm each. No drain hole that I can find. The threads look about as rough as the crank splines do.
For context, the bike is stored outside, though not for years on end. Which is partly why I'm posting: is this a normal amount of corrosion for that, or faster than it should be? If it went in dry from the factory with no drain hole, I could see it going downhill quickly, but I don't have a reference point.
Questions:
- Does yours look like this inside? Especially anyone keeping theirs outdoors. Is this normal for the time, or faster than it should be? I don't have a reference point.
- If you store outside, what actually works? Cover, tarp, shed, or is nothing short of indoors any real protection?
- Has anyone drilled a drain hole in a Unit or Unit X shell? One or two, and what diameter?
- Cavity wax afterwards, worth doing, or does it end up clogging the hole(s)?
Possibly useful:
- Your crank may not match the spec sheet. Mine is stamped MPX 11, which appears to be a Prowheel. Kona's site lists a SRAM NX Eagle PS crank, which uses a completely different bottom bracket standard, so mine isn't that either. Two pinch bolts, plastic preload cap, and I couldn't find a safety plate, so the clamp bolts may be the only thing retaining the arm.
- If yours lives outside and has no drain hole in the shell (which I suspect from the Unit Xs), might be worth pulling the BB sooner rather than later.
Plan: get the threads chased at a shop on drive side, drill a drain hole, paint the edge, wax, reassemble with grease this time. Leaning towards SRAM DUB (+SRAM SX crank) since Prowheel spares seem hard to find.
And covered storage. The freehub also seemed to be barely greased from the factory and has already been replaced.