I’ve got an old Muddy Fox Ti hardtail & the bottom bracket fills up with water, tempted to drill a drain hole in the BB shell but not sure if this is the best idea or what drill to use? Will be fitting a hollowtech 2 type external BB if it makes any difference.

Remove the BB first.

Drill a 7mm hole in the middle of the bottom, deburr both sides and refit BB. Being Ti it will eat your HSS drill-bits, so use a 3mm starter before the 7mm and expect to discard or sharpen them afterwards. Do not use a masonry drill-bit.

Go ride.

Check it is clear every now and again as it can block with mud.

Alternatively block off the top, down and chainstay tubes where they join the BB with builders expanding foam.
With Ti you do not have a potential rusting/corrosion problem.

I have a 22 year-old steel frame that I sprayed internally with a thin oil, then sealed all the external holes in the seat and chainstays.
Greased the seatpost and the BB threads heavily and no water in the BB shell, ever. Worn 3 XT square tapers out in 100,000 miles.

PaulD

Thanks for the advice Paul.

Do not use a masonry drill-bit

this bit made me laugh

7mm is a bit big for a drain hole in my opinion. I’d say 3 – 4mm was more appropriate. Other than that +1 for what Paul said.

I drilled a drainage hole in my old Orange Clockwork well over 10 years ago and it’s still not showing any signs of rust etc. I did coat all internal tubes with ‘duck’ oil too.

Oh a I forgot to add – it might be worth using a ‘punch’ to give the drill some guidance prior to drilling – otherwise you could end up with the worlds most ridiculous signature on your frame 😉

3-4mm is more than adequate and some frames already come with a hole around this size.

I think the water is getting in around the slot in the aluminium seatpost sleave, was tempted to remove this but would then have to go through the process of working out what the id of the seat tube is & get new seatpost. Being Ti there are no holes in the frame so any water that gets in can’t get out. Just removed BB & got the drill out 🙂

Just popped my titanium drilling cherry – a lot easier than I thought it would be, thanks for the advice, gone for a 4mm hole in the end.

I’ve drilled a 4mm hole in all my bb shells that didn’t already have one.
I can’t remember the Ti ones i did being difficult to do.
If your carefull you don’t even have to take the bb out first.