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  1. #1
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    Any one ever see anything like this on a crank spindle?

    This odd spot occurs on the spindle of a set of cranks. This happens inboard of where the bearing race would sit in the bottom bracket - so the bearinrg races never actually touch this spot.

    I contacted the manufacturer and through a set of emails I was told that this is "normal" and happens. I don't ride in water or rain and have never taken any sort of chemical to the parts other than grease.

    So, any one ever see anything like this?
    Attached Thumbnails Attached Thumbnails Any one ever see anything like this on a crank spindle?-crank-shaft.jpg  


  2. #2
    Former Bike Wrench
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    Looks like Galvanic corrosion but you say this area isn't in any contact with Aluminum or the like?

  3. #3
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    I can't think how. The only direct contact to the spindle is obviously the arms which are aluminum and the sealed bearing outer races which are steel.

  4. #4
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    Could the bike have been washed down at some point and then laid on it's side or leaned toward that side? If water got in through the hole in the BB housing and sat for quite a while, pooled in that area corrosion could potentially happen.

    The cloudy residue on the edge makes it look like a water mark rather than a friction-wear mark.
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  5. #5
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    Its not uncommon. Have it on one of my cranks.

  6. #6
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    [QUOTE=isleblue65]Could the bike have been washed down at some point and then laid on it's side or leaned toward that side?

    For the record, I bought these cranks used. There was actually a black, plastic like substance over this area and occurs on a couple of smaller areas. I cleaned the black, plastic like stuff off with fine steel wool in this area thinking it was from old grease or a plastic spacer from the BB. This is what was underneath.

    As far as water, I don't ever wash my bike down or ride in the rain/water. I only clean it with a damp rag when needed. Now what the previous owner did with water and/or washing - who knows.

    If this is corrosion from water, wouldn't it be more "rust" colored since the spindle is steel?

  7. #7
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    It looks like a classic high water mark, from water sitting in the BB for a while at one time or another. Even people who never ride in the rain can get water into their frames which then drains to the BB shell.

    Water usually enters through the seat post clamp area and wicks down past the post. A common scenario is hitting a puddle on a hot day. Water is splashed up onto back of the seat post and seat tube, this chills the frame slightly creating reduced pressure inside and drawing the water in.

    2 things you can do to help.

    1- drill a weep hole into the bottom of the BB shell for drainage, or if you have a screwed on cable guide, remove the screw from time to time. If you're skilled, it's possible to drill a small hole through the bolt itself to make a drain without touching the frame.

    2- use stiff watrerproof grease, or silicone to seal the seat post slot, and base of the seatpost where it enters the frame. This will reduce water entry from the most common source.

    One thing you should do ASAP is remove the bearings from your BB, because the threads are likely undergoing similar corrosion, and if left alone will become nearly impossible to remove later on.
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  8. #8
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    I have no idea how the crank shaft was made, but it looks like a cosmetic defect in a casting that was too deep to be machined out. This would also explain why it was filled with the "black" material the same as the center of the shaft is black.

  9. #9
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    Actually maybe it was the previous owner, but again, I don't ride through puddles, in the rain or wash my bike down - ever. I know the damage water does to even sealed bearings so I just don't let it happen. Just in case, I keep the sleeve installed in my bottom bracket with the gaskets lightly greased.

    I did remove the bottom bracket, which all threads are kept greased so there are no problems there. I do this 2-3 times a year to check the bearings.

  10. #10
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    Quote Originally Posted by gmcttr
    I have no idea how the crank shaft was made, but it looks like a cosmetic defect in a casting that was too deep to be machined out.
    That is exactly what I think. If it was rust or corrosion on steel, it would have a rust color and be "flakey" not "ball" pitted and covered with a black substance.

  11. #11
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    Quote Originally Posted by gmcttr
    I have no idea how the crank shaft was made, but it looks like a cosmetic defect in a casting that was too deep to be machined out. This would also explain why it was filled with the "black" material the same as the center of the shaft is black.
    These spindles aren't cast and machined, but machined from bar stock, and this kind of defect doesn't come from the manufacturing process. As for wondering about the color, that doesn't indicate anything. Not all iron oxides are rust red, many forms are black or chocolate brown, and "black rust" is very common where steel sits in stagnant water.
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  12. #12
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    "Black, plastic like stuff" didn't sound like any corrosion I have ever seen before. With 25 years in commercial construction, I have seen lots of different types of corrosion. Maybe the description wasn't accurate or maybe I just don't know everything yet.

  13. #13
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    Quote Originally Posted by gmcttr
    ...maybe I just don't know everything yet.
    It's really hard to draw conclusions from a vague description. But face it, you haven't known everything since you were a teenager.
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  14. #14
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    Also, that near perfect horizontal line that you see above the corrosion is actually the exact line where the bearing race sits - if that's what people may have thought was a "high water line".

  15. #15
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    Quote Originally Posted by FBinNY
    It looks like a classic high water mark, from water sitting in the BB for a while at one time or another. Even people who never ride in the rain can get water into their frames which then drains to the BB shell.

    Water usually enters through the seat post clamp area and wicks down past the post. A common scenario is hitting a puddle on a hot day. Water is splashed up onto back of the seat post and seat tube, this chills the frame slightly creating reduced pressure inside and drawing the water in.
    It's very difficult to get water into an external BB through the frame. The cups are o-ring sealed onto the centre sleeve.
    The water almost always comes in along the crank axle.

    One of my test riders suffered water intrusion, he rides a nicolai with a completely sealed BB shell.
    Other BB's which I have replaced the bearings in turn up with the outside of the cups and sleeve completely clean but with a rusty high-tide mark on the inside.

    The only real and lasting solution to this is to provide drains to let the water back out. I use a CNC mill to carve drain tracks which aren't visible when the BB is reinstalled but make it impossible for water to pool inside the BB.
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