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How to repair stripped pedal threads: tap, bushing, or replace

By Crankworthy · Published · Updated

Pedal threads that are damaged but still there can be realigned with the correct pedal tap; a tap cannot restore metal that has been removed 12. A fully stripped aluminium arm needs an oversize bushing kit: the bore is tapped to a larger thread and a threaded insert is locked in with strong threadlocker to take the pedal 34. Carbon and hollow crank arms are not candidates for this repair 34.

Left and right pedal threads

Each pedal is threaded for its own side, and the left one is reversed 15.

Left-threaded pedals go on the left crank 1. That is not arbitrary. A pedal axle’s thread is slightly smaller than the thread in the crank, so under load the axle rolls around inside it. With a conventional thread on the left, that precession unscrews the pedal — the problem the left-hand thread was introduced to solve 5.

Park Tool’s advice is to grease the threads of both pedals heavily when fitting them; its tool list names grease or anti-seize compound 1.

The thread sizes, and why the kit matters

Figures from Park Tool, Unior and Sheldon Brown [1][3][4][5]. The oversize thread differs between kits, so always use taps and inserts from the same kit.

Standard pedal thread
9/16 in × 20 TPI, on most pedals and most modern cranks [2][5].
One-piece cranks
1/2 in × 20 TPI [5].
Thread direction
The right side is right-hand threaded; the left side is left-hand threaded [1][3].
Typical pedal torque
About 360 inch-pounds — roughly 40 N·m — according to Park Tool. Use your pedal maker’s figure if it gives one [1].
Park Tool bushing kit
Taps the bore oversize to 5/8 in × 20 TPI to take the bushing [3].
Unior Crank Saver kit
Reams to 5/8 in × 24 TPI; the insert’s inner thread is the standard 9/16 in × 20 TPI [4].

Chasing damaged threads with a pedal tap

For threads that are damaged but still there. In Park Tool’s words, taps will align damaged threads but will not restore metal that has been removed 1.

  1. 1

    Use the right tap for the size and the side

    A 9/16 in × 20 TPI tap for standard cranks (Park Tool’s TAP-6 set has both hands; the left-hand tap is marked LH), or 1/2 in × 20 TPI for one-piece cranks 12.

  2. 2

    Refit the pedal with the threads greased

    Grease or anti-seize on the threads before the pedal goes in 1.

  3. 3

    If no threads are left, stop

    A tap will not help. Park Tool’s advice at that point is to have a professional mechanic install a pedal bushing kit 1.

Fitting an oversize bushing

For a fully stripped aluminium arm. Park Tool recommends having a professional mechanic do this 1; these are the steps its procedure sets out 3.

  1. 1

    Tap the bore oversize

    Mount the oversize tap in a tap handle for even pressure, use copious cutting fluid, and cut right-hand on the right arm and left-hand on the left 3.

  2. 2

    Go straight through; do not back out

    Pass the tap completely through the arm, and do not reverse it back up the freshly cut thread 3.

  3. 3

    Lock the bushing in

    Apply a strong threadlocker to the outside of the bushing, then thread it into the arm 34.

  4. 4

    Set it slightly recessed

    Position the bushing just below the outer face of the crank, so none of it shows 3.

  5. 5

    Let it cure

    Allow the threadlocker to set up and dry — several hours — before greasing and installing the pedal 3.

From the catalog

Grease for the pedal threads, a puller for removing square-taper and splined arms, and replacement cranksets for when an arm cannot be saved.

What this job needs that we don’t stock

Named so you can source them elsewhere — we would rather say this than point you at a product that is not the right one for the job.

  • Pedal taps (9/16 in and 1/2 in) and oversize bushing kits — neither Park Tool’s nor Unior’s is in our catalog.
  • A torque wrench that reaches pedal torque. The one we stock tops out at 14 N·m, well short of the roughly 40 N·m a pedal needs.

References

  1. 1.Pedal Installation and Removal — Park Tool (thread sizes, direction, torque, grease, when a tap will not help)
  2. 2.TAP-6 Pedal Tap Set (9/16 in) — Park Tool
  3. 3.Pedal Bushing Repair Kit Procedure — Park Tool (5/8 in × 20 TPI, strong threadlocker, not for hollow or carbon arms)
  4. 4.Crank Saver Kit 1695MB1-US — Unior (5/8 in × 24 TPI inserts, not for carbon-fibre arms)
  5. 5.Pedals — Sheldon Brown (thread sizes, why precession unscrews a conventional left pedal)

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