crooked cranks

I switched a few unis to 4" cranks over the weekend, but I’m having trouble with one set.

The first set (set 1) I put on seemed to give a wobbly ride. The pedals seems to be moving in and out as they moved around, as if the line passing through the crank axle wasn’t parallel to the line passing through the pedal axle.

I put the second pair (set 2) of cranks on the same unicycle with the same pedals and it seemed that the wobble went away.

On to the second unicycle. I had 5" cranks and the United pedals. These seemed to work fine. When I replaced the cranks with set 1, using the same United pedals, I got the same type of wobble.

My assumption at this point was that the cranks were bad. I examined the crank axle and it appears like new. There are no scratches, gouges or anything suggesting damage. The original 5" cranks also slip on completely, all the way on the axle taper. The set 1 cranks don’t get all the way on, they stick out an additional 3/16" or so. I also only get about a half to three quarters turn when tightening the crank nut.

I went back to the bike shop where I bought the cranks to exchange them. The new cranks (set 3) gave the same effect. In the process I must have pissed of the owner of the shop. He seemed to believe that the pedals were to blame. Apparently you can’t resell cranks that have been tried out! We tried a new set of pedals and it seemed to help, so I accepted the new set.

I got home and did a little more riding. It seems the United cranks are flat, whereas the new pedals have a depression over the center of the pedal: the edges are higher than the axle of the pedal. I think this depression allows some foot flex to mask the wobble, but not sure.

I put on a similar set of the pedals at home, thought the wobble had gone away, but after riding a little more discovered they still wobbled with set 3.

The hub is a Suzui U-12.

Any advice? Tests? I can’t seem to quantify what I am feeling and the shop owner doesn’t ride.