Bottom Bracket Fixed Cup Gap?
Davy
creak from the bottom bracket when the left pedal is at the 11 o'clock
position.
The fixed cup when screwed in does not bed down squarely on the frame -
difference of 0.8mm between opposite sides (equivalent to about one thread
pitch). Is this within tolerances?
But if I really tighten it down then it does go down flat; but them
presumably the cup is distorted to fit the bracket, and so also will be the
ball bearing surface?
When I rotate the axle by hand it seems to have a slight wobble in it.
Anyone any idea on how I can check if the axle is straight? Rolling it on
glass does not work since the bearing flanges act as wheels and hold the
axle surface off the glass.
many thanks
Davy
Simon Daw
"Davy" <da...@REMOVETHISchobham.org.uk> wrote in message
news:TZKdndPT55R...@brightview.com...
> I am renovating my 1950s Elswick-Hopper Lincoln Imp but am experiencing a
> creak from the bottom bracket when the left pedal is at the 11 o'clock
> position.
>
> The fixed cup when screwed in does not bed down squarely on the frame -
> difference of 0.8mm between opposite sides (equivalent to about one thread
> pitch). Is this within tolerances?
I've seen worse, but it's not ideal. Sounds like one of three things - dodgy
thread on cup; dodgy thread on frame; bottom bracket shell not faced
properly. Much more likely to be one of the first two, given that it's an
old frame. Is the cup loose in the shell? Try another cup and see if it's
any different. (Make sure it's a decent one...)
> But if I really tighten it down then it does go down flat; but them
> presumably the cup is distorted to fit the bracket, and so also will be
the
> ball bearing surface?
Cup able to move in threads allowing it to fit flush? Sounds like the dodgy
thread idea to me.
> When I rotate the axle by hand it seems to have a slight wobble in it.
> Anyone any idea on how I can check if the axle is straight? Rolling it on
> glass does not work since the bearing flanges act as wheels and hold the
> axle surface off the glass.
Difficult. I presume it's the left side that's possibly out, because it's
normally pretty easy to use the chainring to assess this if it's the right.
(If it *is* the right, and no deviation is evident in the ring, or any
deviation is obviously the ring itself, don't worry about the axle.) If it's
possible (which it may not be), fit the r/h crank to the l/h side to use it
to check.
Your problem could well be a dubious thread on the adjustable cup side. If
it's loose (which it must be slightly, to take up the 0.8mm), it's probably
moving slightly in the frame. See what changing the cup does; if other cups
are the same, you have a bigger problem. Might be possible for a
framebuilder to sort it out - usually needs a bit of braze in the thread
followed by a retap. Or you could have it reamed and converted to Italian
thread, if the shell's thick enough (and you can get 36x24 cups to match
your axle or chainset, which might not be at all easy).
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Simon Daw
"Simon Daw" <simo...@NOSPAMmsn.com> wrote in message
news:c46rhv$2cs$1...@news7.svr.pol.co.uk...
> Your problem could well be a dubious thread on the *adjustable* cup side.
Fixed cup side, even!!