stupid rack / mudguard bolt question

metmanmark
metmanmark Posts: 28
edited March 2011 in The workshop
OK - this is probably a daft question but here goes. The bolt that goes through the rack & mudguard has come out. This happened last autumn so I wrapped some plumber's tape around a new bolt and fitted that. This has now worked itself loose again. This evening I tried putting a new bolt through and using a nut on the other side to hold it in place. However this is happening on the same side as the gears so it catches on the chain. I tried putting the bolt in both ways (ie with the nut on the inside and then turning the bolt round so the nut was on the outside) but to no avail.
Any top tips? Clearly the thread on the bike has stripped - can I get a new slightly bigger bolt to fit or am I missing something obvious.
Will take a rucksack tomorrow as I don't want my pannier pulling the rack to oneside.
Cheers
Mark

Comments

  • rja
    rja Posts: 78
    You could try some Loctite, put some on the thread and away you go!

    http://www.loctite.co.uk/cps/rde/xchg/h ... g-4476.htm
  • MichaelW
    MichaelW Posts: 2,164
    The bolt comes out due to precession, a weird redirection of forces which can remove bolts completely. I thought it was vandals or kids messing with my bike at first.
    Your threads may still be OK. My solution is a serrated star washer.
  • The Rookie
    The Rookie Posts: 27,812
    Precession is an effect due to gyroscopics, I doubt the whole bike is spinning fast enough to cause precession of the bolt - sorry that's the stupidest comment I've heard in a long time! :lol:

    Plumbers tape, aka PTFE tape (aka teflon) one of the slipperiest man made substances, not the best choice to keep a bolt in place. Loctite is the stuff, that or get the hole drilled and tapped one size larger.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • ride_whenever
    ride_whenever Posts: 13,279
    Unfortunately you're wrong, mechanical precession comes from contact forces and is the relevant process here...

    have a read of this it's a different process.

    PTFE tape should indeed work, but loctite is usually a better bet
    Neeermad
    Carbon 456
    456 lefty
    Pompino
    White Inbred
  • desweller
    desweller Posts: 5,175
    I think I remember your 'taped screw' thread!

    You could drill it out and tap it for a bigger screw. Bit surprised that the nut is fouling the chain; I have successfully used nuts on drive-side eyelets before, although I've had to trim the screws down so they do not stick out beyond the nut. You might be able to get a thin nut or grind the nut down if you have the tools. Got any pics?
    - - - - - - - - - -
    On Strava.{/url}
  • Blue Meanie
    Blue Meanie Posts: 495
    Work with the wheel removed and chain/mech covered up, insert bolt (m5?) from the wheel side and use a nylock nut on the outside - make it good and tight. File (carefully) most of the head off the bolt and jobs done.
    I normally use masking tape all over the stays to avoid marking the frame from my filing.
    Any LBS will have buckets of stainless steel m5 bolts, washers and nylock nuts.
    FCN16 - 1970 BSA Wayfarer

    FCN4 - Fixie Inc
  • The Rookie
    The Rookie Posts: 27,812
    ride_whenever wrote:
    Unfortunately you're wrong, mechanical precession comes from contact forces and is the relevant process here...

    have a read of this it's a different process.
    Fair does, still no rotating force though, so no precession unless as I said the bike is spinning round the bolt or the mudgaurds round it.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • metmanmark
    metmanmark Posts: 28
    Thank you Blue Meanie - I will probably follow your suggestion (at the weekend). It is probably going to take quite a while to file the bolt down to the required thickness but it is a solution.
    Cheers
    Mark
  • Blue Meanie
    Blue Meanie Posts: 495
    Nae Bother, and err, it's m4.

    20mins in a workstand to do a neat job
    FCN16 - 1970 BSA Wayfarer

    FCN4 - Fixie Inc
  • MichaelW
    MichaelW Posts: 2,164
    The precession of the rack bolt is caused by fretting, not rotation. The bolt is subject to cycling loading (loading and unloading) whenever you go over bumps and rough ground.

    You also get fretting in the pedal spindle where there is no rotation force cause by pedalling, only cyclical loading. We use a reverse thread to ensure that the resulting precession tightens the spindle rather than loosens it.
  • jejv
    jejv Posts: 566
    MetManMark wrote:
    This evening I tried putting a new bolt through and using a nut on the other side to hold it in place. However this is happening on the same side as the gears so it catches on the chain.
    Google: button head allen bolt
    That's more likely to work with the bolt head on the chain side. I haven't tried this yet - wondering when I'm going to have to.
    BZP would be better than stainless on an aluminium frame.

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