# Drain Hole in Bottom Bracket for Carbon Fiber?



## robokayaker (Jul 5, 2004)

Over the years of reading the recommendations of good mechanics, I have become a big believer in drilling a small drain hole in the bottom of the bottom bracket shell. In Northern VA, a bike wash is necessary practically every ride. Without a drain hole in the frame, water just builds up unable to evaporate in the BB shell. Several years ago, I took apart my best ride of the time (a Jekyll) to find the bottom bracket swimming in a few ounces of water. When I drilled that one (just a tiny hole), I observed after a thorough washing a few drips coming out of the hole while I was drying off the bike on the stand. I know it is effective in aluminum and steel frames. My cross bike, for example, is steel and obviously has to be washed every time out. On my Ellsworth Truth (aluminum), the drain hole also works great.

Now before I go on, I know people will write back and say I am washing the bike wrong, so let me elaborate. I put the bike on a repair stand and gently wet everything with water (no pressure spray). I then brush mild soapy water onto everything with a paintbrush. I brush all the drive train components with a firmer brush. Then I do a low pressure rinse. The real cleaning comes by rubbing the bike down with a towel and rubbing the drive train components with a rag. I then lubricate and oil as necessary.

Having said all that, here is my question. I am now investing in a carbon fiber frame, A Scott CR1 team issue road bike. This will be my first carbon fiber frame. I'm really afraid of creating a stress riser in the BB by the small hole. Can anyone give me some advice or data based on your experience with drain holes drilled in carbon fiber BB shells? Thanks.


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## flipnidaho (Aug 10, 2004)

*There is an article*

in cycling news that showed the Team Discovery bikes having a hole drilled in the bottom of the bb shell for the same reason (and if you can imagine the stress those bikes go through, it would seem safe-granted they are replaced every year). However, if I was in your shoes, I would just pull the non-drive side crank and bearing every other month to check on them (assuming you go with outboard bearings) instead of drilling the bb shell. Also, road bikes, even out East, should not need the frequent washing that mountain bikes do.


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## archer (May 20, 2004)

I think I'd flip the bike on the stand and pull the seatpost periodically. Change the angle as required to get the water out. 

I would not drill composites if I didn't have to.


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## Full Mountain (Mar 30, 2005)

drilling in composities can cause delaminations of the plys and on top of the stress created by the hole
DMR


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## SSTed29r (May 27, 2004)

The BB shell on the CR1 is all Aluminum, drill away.
They are wrapped with the carbon, but the shell itself is alu.


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## loosch (Feb 16, 2005)

Whilst drilling holes in Composite is best avoided if possible, there are plenty of examples of succesful drilling. A Boeing 777 rudder skin (Carbon fibre with Honeycomb) has hundreds of drilled holes in it.
The key is to let the drill do the work ie. DON'T push the drill thru, let it cut, the right drill (a dagger type) is also good but a sharp twist bit will do.
So get a new 1/8" bit and take it steady.

Hope this helps.


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