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I commute to work every day and lock my bike on the street.

I have a nice saddle so I remove my seat post and take it into work with me.

This obviously leaves a hole open to the inside of the aluminium frame. Living in London it often rains. Should I worry about raining getting into the frame by this hole and doing damage? And if so what should I cover the hole with?

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    The danger is to the bottom bracket. Water gets in and corrodes the bearings. For some stupid reason a lot of bikes don't have a drain hole on the bottom of the BB housing. Cover the hole with a plastic bag, a cocktail umbrella, whatever. – Daniel R Hicks Mar 23 '16 at 12:49
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    Spray some wax-based coating down the tube to slow oxidising and maybe a (champagne) cork to close the top – Carel Mar 23 '16 at 15:32
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    Periodically roll the bike up onto the rear wheel and empty the water out. That's worth doing even if you don't take the seatpost out every day. It's easy to do, position yourself as though you're going to wheel the bike somewhere, squeeze the rear brake, pull the bike backwards and lift slightly on the handlebars, the bike should end up on it's rear wheel. Stand to one side, if water does pour out of the seat tube it'll be dirty. – Móż Mar 23 '16 at 21:04
  • when you lock the bike up flip the bike upside down, problem solved – John Burgess Jan 8 '18 at 17:18
  • A good thing to cover the hole with is a piece of an old tube. If you cut a small rectangle out you can wrap and tie it easily. I started using one around my top cap in rain to protect the head tube bearings and it has worked great. – ebrohman Jan 8 '18 at 19:08
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It depends on the frame material what effect the water inside the frame will have. A lot of frames have a small hole drilled at the bottom of the bottom bracket casing. If there is no hole there you can drill one yourself. I have done this on aluminium frames before and it is very easy. Use a 4mm drill bit and drill through till you cut into the bottom bracket void. There will be a gap internally between the frame casing and the actual bottom bracket. A hole this small in the centre of the bottom bracket casing will not affect the strength of the frame but will allow water to drain. I have found frames fill up with water even with the seat post in place if ridden in the wet, so putting a cork in the seat post hole probably won't make much difference.

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I drilled out aluminum frame and then inserted removable plug , as water has ruined three bearings and once was from ice caused by zero temp operations.

  • Sub zero weather is a great way to find out where water has infiltrated where it shouldn't be. For example, one bike with full length brake cables had a pool of water inside which literally froze the rear brake on one position. – Rider_X Jan 8 '18 at 21:16
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Bottom bracket and the inside of the frame might get oxidised (rusty). Cover the hole with a plastic bag or something else, to prevent rain from going inside your frame.

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