Pedal Wrench for a Bicycle

I began to feel a little knock in the left pedal on my old 10-speed and thought the bearings may have loosened.  But, when I examined it, I saw that the pedal shaft had begun to unscrew itself from the crank.  I have a suitable pedal wrench at home, but that bike is kept in another state for times when we visit there.  Because I have the necessary tools and scrap materials, I decided to make my own.

I have a piece of scrap steel 5/32 inch (4 mm) thick.  It is a little harder than most steel and seemed ideal for making a pedal wrench.  It is thin enough to fit the narrowest flats on pedals and yet thick enough that it will not bend away.  

If it were a long bar, I could simply cut my wrench into one end of the bar.  I chose to cut off a piece of steel, form a wrench into it, and weld that to a bar for leverage.

I like to apply a piece of masking tape to steel and mark it with a fine point marker.  I am using a cutting wheel in an angle head grinder.  My steel is 2 7/16 inch wide.  I am cutting a 1 inch piece from it for my wrench.  Make it any size you like.

I applied a new piece of masking tape and marked the mid-point in the piece of steel.  Then I marked two vertical lines to define the sides of the wrench opening.  I cut two slots just under 15 mm apart at their outside edges.  Most pedal flats accept a 15 mm wrench.  Some are 9/16 inch.  9/16 inch is only 0.72 mm less than 15 mm.  In a pinch a 15 mm wrench can be used on a 9/16 pedal flat, or add a shim from a very thin piece of a can.

I clamped the portion of the steel I want to use in my vise.  I clamped a locking pliers to the part I want to remove and rocked it back and forth until it broke off.

My wrench piece was too tight to slide fully onto the pedal flats.  I would need to make the opening a little wider, but not by much.

Although discouraged, I sometimes do a little light grinding on the side of an abrasive cutting wheel.  It made a good way to remove just a little material so I could fit the wrench for the pedal flats as in the previous step.  I also gave the bottom of the opening the shape of an arc so it better fits the rounded portion of the pedal shaft.

I had a piece of rod 7/16 inch in diameter and 11 inches long that would make a suitable wrench handle.  Holding a flat piece of steel in place for tack welding is much easier and more precise when a small spring clamp like the one here is used. 

After tack welding the wrench head to the steel rod, I removed the spring clamp and changed the wrench's position to make welding easier.  I welded both sides and removed the slag. 

The heat of welding did narrow the wrench opening just a little and I had to go back to step 5 to size the opening for the flats again. 

You can customize your wrench by setting the wrench opening to an angle so the handle has a better mechanical advantage when removing a stubborn pedal.  Remember that as you face the outer end of a pedal, the pedal on the right side tightens when the wrench is turned in a clockwise direction, while the pedal on the left side of the bicycle tightens in a counter-clockwise direction.

The heat from welding seems to have softened my steel just a little.  Should the steel deform over time from pressure against the flats, I can always add a little weld bead on the affected area and grind it to size again as in step 5.