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I have a bottle cage on the upper side of my downtube, and yesterday I noticed that one of the screws has gone missing. I don't know when this happened, but it could have been months ago. I often leave my bike parked in the rain, so I'm now concerned that water has entered the downtube through the exposed screwhole and settled in the frame, which is made of steel.

How can I check if there is water ingress and minimise any damage? My first thought is to turn the bike upside down for a few hours and let any water drain out, but is there a better way and/or more I could do? I would like to stop any rust in its tracks.

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  • Make sure the drain holes (there should be at least one) on the bottom of the bottom bracket are clear. And, if you have the skills, take apart the bottom bracket and give all surfaces a coating of grease.
    – Daniel R Hicks
    Commented Jan 29, 2018 at 23:07
  • Damage is done by moisture, in quantities too small to be called water and not enough to drip out. Storing the bike in the warm helps dry the inside, and for forced-drying you can push warm low-pressure air through the frame if you have a low pressure compressor. You could even use a track pump down the seat tube with some packing to seal around the hose. (will try this later)
    – Criggie ♦
    Commented Jan 30, 2018 at 0:04
  • @Criggie - Carelessly using a compressor could make things worse, as moisture in the air condenses when the air comes out of the compressor hose.
    – Daniel R Hicks
    Commented Jan 31, 2018 at 20:16

2 Answers 2

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Water will always find a way to enter the frame, if not through the bolt hole then via the seat tube or head tube or gas exhaust holes. Turning the bike upside down will not be very effective unless you fall into a river often. What you can do is 1) make sure that water has regular ways to leave the frame; 2) use special coatings on the inside surfaces to inhibit or prevent rust ; 3) perform regular maintainance to prevent bike parts from binding together.

The lowest point of the frame is its bottom bracket shell. That is where all water tend to come. Check if the frame has a hole there so that water can drip out.

You will need to strip your frame before applying a rust inhibitor. See a good guide here: https://surlybikes.com/info_hole/spew/spew_care_and_feeding_of_your_steel_frame

Lastly, you should put grease at the places where the frame holds other parts: bottom bracket threads, seatpost, quill stem (if you have a threaded one ). That would prevent parts rusting together, making it impossible to detach them later.

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    It was my understanding that frame saver / rust inhibitor should be applied at the start of the frame's life, before any rust has formed. I am not clear on the efficacy of applying it after rust has begun. It also require the OP to strip all the components off the frame which is a sizeable task. That said, even with water infiltration it will likely take decades before any structural problems emerge.
    – Rider_X
    Commented Jan 29, 2018 at 18:48
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    perfect answer except for one detail - if there's no drain hole at the low point of the BB shell, always make your own :)
    – Nathan Knutson
    Commented Jan 29, 2018 at 21:04
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I would pull out the seat-post and flip the frame over to make sure no water is inside. Then let the bike dry out in a warm and dry environment for a few days.

For a quick and dirty fix:

  1. Take the bike outside and spray a bunch of Fluid Film inside the steel frame tubing and let it soak in.
  2. Turn over and drain out any excess (if any and dispose of properly). This stuff seems to work great and stops metal from further degradation.

(Read Amazon reviews and other product info about safety precautions.)

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