Woodruff Key Removal And Replacement

old key, new key!

A woodruff key is a semi-circular key that is very irritating to remove if it s sheared off, because the slot cut for it is round- you cant just push or pull the key out like you would with a square keyway.  Shearing, of course, something that would happen to a 50 year old moped.  I started noticing wear on the key, and in a flash it was totally gone!  Completely sheared off to the level of the crankshaft, where it is supposed to engage the flywheel to create sparks/power lights.  So of course the solution was to order a new one from treats, who shipped really fast (and is not the company who took forever to ship).

If you look closely, you can see the key that is totally sheared off in the shaft.

Once the key was in my hot little hands,  I was stuck with the task of removing the old key.  This was a daunting task- I don’t know how much abuse the bearings on the crankshaft can take, and the solution to stuck/sheared keys involves a hammer, a punch, and a steady hand.  The trick is to smack one side of the key and use it as a fulcrum to get the semicircle to rotate in its seat.  Once one side is sticking out, the key can be further loosened by smacking it so that it rotates back and forth, until it can be grasped by pliers or vice grips and yanked out.  Unfortunately, the key tends to be small- mine was 2.4 mm across, which meant that beefy punches were out of the question.  You definitely want something beefy like a center punch for this, because a pin punch of such a small diameter will bend.

After some judicious smacking, the key came loose

Once mine got a little looser, I  managed to grip it with pliers and pull it out.  It was surprisingly not that hard.  The last step was to install the new key in the slot.  True to form (for this project) it was a little small in the width department, and a little tall in the height department, so some loctite and filing may be in order.  Despite that, the new key is pretty good as far as rotating the piston/chain/magneto so I am optimistic that this will solve my no-spark issues.

Happily installed in the flywheel.

3 thoughts on “Woodruff Key Removal And Replacement

  1. Richard Cooper says:

    This is a great help: the only result for a search on how to remove a key from a keyway!
    How can one find out whether it is a Woodruff key or a rectangular key without access to the original specs. The key I have to remove is in an old Massey Ferguson Tractor front axle king pin.

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