I've been hit by bimetallic corrosion…

well not me my bike…

Problem is:

Carbon frame, with Ally insert, in to wich is threaded (and staying there) a steel BBkt cup….
Carbon – can't use heat or jst an even bigger hammer…
so far GT85 etc not having any effect…

Any magic suggestions would be very much appreciated…

(BTW bought 2nd hand, so I didn't forget the anti-seize!)

Thanks

is the axle out? can it come out?

You could try putting a hacksaw blade through the hole for the axle then cutting through the steel cup to JUST above where the thread would kick in … Essentially cut it into quarters and knock the cup out?

What sort of frame is it? as you may be able to get a replacement alloy BB insert?

can you get the cup on either side out – if you can then lots of plusgas down the bb from the other side would be a good start then leave frame on side to 'soak' for a day or two.

Have you tried sticking your BB tool in a vice, sticking the bike on top and using the frame as a lever?

Best to leave the WD-40 to soak in overnight first, then try it gently and with 'progressive' pressure, rather than bouncing with full bodyweight on it! 😉

GT85? Pah!

Seatpost out, plusgas in, come back a few days later with a big justy and a length of pipe. Pray the ally insert is bonded better than the corroded thread.

Otherwise, I'm sure tipping the plusgas out, tipping in boiling water, then tipping that out and tipping in v cold water will be enough to crack the thread and not do any damage to the carbon. Blowtorches obviously out, but boiling water should be OK.

'tis a trek carbon road frame.

the rest of the BBkt is out, just the right hand side cup, so maybe a saw would eb good.

Is plusgas something special? ie better than WD40, coz I've being soaking in WD40 and GT85 for a week or so….
🙁

Thanks folks….

plus gas is 'thinner' than wd40 etc and is designed to find it's way down threads. you can get other stuff too that does a similar job – go to your local motor factors and ask.

I'd persever with somethign that doesn't involve cutting for a bit too.

anything that will heat the aluminium quickly will help as the steel will take longer to expand.

You may want to get in touch with either Colin or Gareth at Trek in the Technical workshop! They can probably advise.