Praxis Works PF30 problem

DeVlaeminck
DeVlaeminck Posts: 8,746
edited July 2017 in Workshop
Got a shop to convert my PF30 BB last summer with a Praxis Works adaptor. Now for various reasons I haven't ridden the bike since then until this week (except for a run round the shop car park with flat pedals) and I'm getting a slight creak and some chain ring "run out" although in a bike stand spinning the cranks by hand the chainring seems to run straight.

On inspection there is a gap of maybe 1mm - clear enough to see daylight between it and the frame- between the frame and the Praxis Works cup on the drive side and I believe that is allowing a slight flex under power giving rise to the creak and the appearance of a bent chainring and the chain rub on the front mech.

Can anyone with more experience of these things (or less experience if you like - all opinions welcome!) advise if I'm likely to be right about the cause of the problems? Thanks
[Castle Donington Ladies FC - going up in '22]

Comments

  • sungod
    sungod Posts: 16,577
    is this the adaptor that screws together?

    i.e. this type...

    praxis_BB_schematic-01.jpg

    ...for pf30 there's a plastic shell that surrounds this inner metal bit

    the adaptor is pressed in from one side, then the other side is screwed in which expands a collet to hold it all in place, there's a stop in the assembly which prevents tightening beyond the designed point - if there's a gap it may have been installed incorrectly or be incompatible with the frame

    it doesn't 'clamp' the bbshell from the sides, one side is still press fit, the other expands to become the equivalent of a tight press fit, to me that's bizarre for something apparently intended for people trying to eliminate problems with a press fit bb, and i've seen posts reporting creaking with these adaptors

    imho the wheels mfg design looks better, it clamps the bb shell...

    http://wheelsmfg.com/bottom-brackets/pf ... ckets.html
    my bike - faster than god's and twice as shiny
  • k-dog
    k-dog Posts: 1,652
    If the gap is on the drive side then surely it just needs tightend - that will pull that side in and also expand the collet a bit which should stop it moving?
    I'm left handed, if that matters.
  • DeVlaeminck
    DeVlaeminck Posts: 8,746
    Yes it's one of those screw together type, the shop suggested it and they seemed to have good reviews on this forum hence going with it.
    [Castle Donington Ladies FC - going up in '22]
  • sungod
    sungod Posts: 16,577
    k-dog wrote:
    If the gap is on the drive side then surely it just needs tightend - that will pull that side in and also expand the collet a bit which should stop it moving?

    you'd think so, but the two parts do not clamp the bb shell, there's a stop preventing that (unless of course the shell is wider than pf30 spec.)
    my bike - faster than god's and twice as shiny
  • k-dog
    k-dog Posts: 1,652
    Yeah, but if it's creaking that surely means that the collet hasn't been expanded enough - and the way to expand it is to screw it in a little?
    I'm left handed, if that matters.
  • Flâneur
    Flâneur Posts: 3,081
    May be worth calling Praxis, were really helpful when I did regarding the BB on my S works
    Stevo 666 wrote: Come on you Scousers! 20/12/2014
    Crudder
    CX
    Toy
  • sungod
    sungod Posts: 16,577
    k-dog wrote:
    Yeah, but if it's creaking that surely means that the collet hasn't been expanded enough - and the way to expand it is to screw it in a little?

    it only expands at the collet end, which must be tightened until it hits the stop during installation, it cannot be tightened further

    the other end is just pressfit, tightening the collet end will do nothing to change that

    unfortunately, pressfit can creak
    my bike - faster than god's and twice as shiny
  • DeVlaeminck
    DeVlaeminck Posts: 8,746
    Took it back to the shop, they agreed it doesn't look right with the gap, we'll see what happens hopefully just needs tightening up a bit.
    [Castle Donington Ladies FC - going up in '22]
  • DeVlaeminck
    DeVlaeminck Posts: 8,746
    Right, they tigjtened it up but said they couldn't get it to bottom out, seemed confident it wasn't going to move but still a noticeable gap between converter and frame. On riding it is better but still getting run out under power and chain rub. It isn't creaking but I'm pretty sure the chainrings shouldn't look like they are bent under power.

    I think I can move it grabbing the cranks and putting some side to side force in but it's hard to tell if it's just flex in the bike.

    Worst case if this isn't going to work is the wheels manufacturing version a safe bet? Just getting back to riding after a year off the bike and a constant noise from the drivetrain doesn't help rekindle my love for the bike!
    [Castle Donington Ladies FC - going up in '22]
  • sungod
    sungod Posts: 16,577
    fwiw i've used the bb30-out version of the wmf one to run a gxp pm in bb30 frame, easy to fit, no problems at all
    my bike - faster than god's and twice as shiny

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