re-tapping mudguard fitting

Discussion in 'Bicycle Mechanics and Repairs' started by alecstilleyedye, 6 Apr 2018.

  1. alecstilleyedye

    alecstilleyedye nothing in moderation Moderator

    the boardman alu frame i have has stripped the threads on the lower of the two mudguard/rack mount holes.

    at the mo i've got the rack in the good upper hole, and used cable ties to secure the mudguard in the lower stripped hole.

    can the stripped hole be re-tapped, and if so would it need a thicker bore of bolt?
  2. Hugh Manatee

    Hugh Manatee Veteran

    Depends how much material is left. Funnily enough, I am looking at my tap set right now. What bolt is it supposed to take?

    M3 needs a 2.5mm hole.
    M4 needs a 3.3mm hole.
    M5 needs a 4.3mm hole.
    M6 needs a 5.0mm hole.

    The trick to make sure the hole is as close to required size as possible. With my project, this mean a hand reamer but mostly just means checking the drill bit and keeping it straight so as not to open the hole up too much.
  3. Vantage

    Vantage The dogs chew toy

    You've 2 options here.
    1: If you retap new threads in, you'l need a bigger bolt. A drill bit about 1/2 a mm smaller than the new bolt will be needed and take your time during drilling and tapping.

    2: Easier option is to just drill for a bigger bolt and use a nut to hold it in. I used this method for my rack mounts.
    robrinay and dave r like this.
  4. Oldfentiger

    Oldfentiger Über Member

    Pendle, Lancs
    3rd option is to buy a helicoil kit.
    I bought one and it’s been invaluable.
  5. wisdom

    wisdom Veteran

    If you can get to both sides the easiest option by far is a nut and bolt.Possibly a nyloc nut.Thats the way I would go.if it' a boss not a through thread then it would have to be drilled and tapped.if it's aluminium then easier to drill and tap but don't overtighten it or you will be back to square one.
    raleighnut likes this.
  6. OP

    alecstilleyedye nothing in moderation Moderator

    tried that but found it too fiddly (i.e. couldn't be arsed taking the wheel off)…
    Vantage likes this.
  7. Ian H

    Ian H I am an ancient randonneur, & I stop often for tea

    East Devon
    Use longer bolts and mount the mudguard on the same hole as the rack.

    Otherwise, tap out to M6 and use appropriate bolts.
    User45 likes this.
  8. boydj

    boydj Guru

    But you should only have to do it once, unless you're taking the mudguards on and off regularly. You don't even have to drill it out, just use a longer bolt. I've had to do this and didn't have to take the wheel off.
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