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boom stuck!

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revchrisu View Drop Down
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    Posted: 26 June 2020 at 6:14pm
I have just acquired an aluminium frame low racer with a carbon boom.
I need to extend the boom or cut my legs shorter.
Currently the later option is looking more likely...

I have of course takebn the bolts out, hung the bike from the bottom bracket and squirted wd 40 and a drop of 3 in 1 at it.

I have even put a strop on in and used a sash cramp to try to push it in a little... (without too much load as I am scared of crushing the carbon)

What's next?
Ta.
C.
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Yanto View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 28 June 2020 at 4:12pm
This may sound daft but try knocking it in with sharp high speed taps with a hammer. It is the bond you are trying to break. I was going to suggest heat but I don't know what the relative coefficient of expansive is for Al v CF.




Edited by Yanto - 28 June 2020 at 4:13pm
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revchrisu View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote revchrisu Quote  Post ReplyReply Direct Link To This Post Posted: 28 June 2020 at 5:43pm
I shall give that a try, ta.  I have used a hammer over a piece of wood to soften it, but maybe it needs it without the wood padding.  I shall let you know...
C.
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Balor View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 28 June 2020 at 9:49pm
Al is pretty large positive and CF actually slight negative.
So if boom is 'sleeved' inside aluminium frame, heating it should work (just don't overdo it).
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Post Options Post Options   Thanks (1) Thanks(1)   Quote KM2 Quote  Post ReplyReply Direct Link To This Post Posted: 28 June 2020 at 10:31pm
Has the main frame welded on bosses , one threaded?
If so, push the bolt through the first boss , usually not threaded. Slide a nut between the two bosses and thread onto the bolt. Then thread the bolt into the threaded frame boss, whilst keeping the nut in the centre of the bosses.
Once you have the bolt in the threaded frame boss enough to spread the load, you simply advance the nut against the non threaded frame boss to push the two frame bosses apart.
Do it gently, worked on a Streetmachine, but do it at your own risk.
Gently does it.
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Yanto View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 29 June 2020 at 7:50am
One other more drastic method is to remove the BB, put through the housing a length of strong wood (making sure the threads are very well protected) and lever it, need somebody to hold the rest of the bike to stop it twisting, at this point though you are into the territory of last resort!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 29 June 2020 at 2:00pm
I think that the bond must be a purely mechanical one caused by the temperature change from when the boom was inserted into the frame. So gently heating it should work. Preferably while someone else tries twisting the boom at the same time.

Good luck.
Roy 
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revchrisu View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote revchrisu Quote  Post ReplyReply Direct Link To This Post Posted: 30 June 2020 at 8:29am
All sorted!

I wrapped the boom in a tea towell and then wrapped that in plastic but left a hole in the top.
1 kettle of boiling water later and the boom eased out pretty easily.

Thanks for all the wisdom.Smile
C.
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Kim View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kim Quote  Post ReplyReply Direct Link To This Post Posted: 30 June 2020 at 1:00pm
Nice!
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Yanto View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 30 June 2020 at 5:22pm
Well done and fine example of creative thinking Lamp
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