Crank arms destroyed

I made the (foolish) decision to leave my unicycle in the Phys. Ed teacher office so I could use it for class. When I came in to grab it, everyone was talking about how they were trying to ride it etc etc. After closer inspection, the pedals had become loose and the thread was completely torn up. Nothing left for it to grab onto. The uni was a Nimbus II with Qu-Ax 125mm ISIS cranks. Pedals were Snafu somethings. The pedal is fine but the crank is destroyed. Do I have any options other than to buy a new set?

Did you have permission to leave it there? If you did, they shouldn’t have touched it… You might be able to talk to the Dean, or principle, or even the phys ed teachers about the situation. It’s worth a shot.

You can have the thread repaired by heli-coiling it.
A LBS should be able to help you.

How could they get loose?
did you have the seat pointing the wrong direction, so the left pedal was on the right side?
that would cause them to loosen.

That will be more expansive than a new set of Cranks.

That really depends on the cranks.
Maybe we pay too much in Australia?

A set of Qu-Ax ISIS cranks would cost 4 times the price of the helicoil, including labour.

If you’re talking square taper steel though, you might be right.

Using helicoils is common to fix stripped threads

You drill out your stripped threads, then work in a tap to create new larger threads, this is a lot of work. Then screw in the new helicoil insert.

Don’t do this on a unicycle IMhO. The helicoil thread repair kit is a solid and good fix in many engine applications. It is crap all for a uni crank.

Really, once your uni crank looks bad, just buy a new one. They can be fixed, but it is unlikely to be worth the effort, $ wise.

I did have permission. I plan on bringing it up with them but was looking for an easier fix. If there is none, I will simply buy new ones. Thanks everyone.

Neither was the case. I do not know how they got loose…

Maybe the rider(s) sat on it backwards?
Or maybe the pedals just weren’t tight enough.
Either way the rider(s) didn’t recognize the funny feeling of loosening pedals.

A friend of mine had the same problem on a bike. First ride out, his pedal destroyed the crank arm threads. He only spoke up after the pedal was basically falling off. “I thought something felt strange earlier…”, he said. Too bad he didn’t stop earlier.

Sorry your uni got messed with.

Hard drops can loosen pedals

A 15 mm wrench should be your friend. It is always a good idea to check pedal tightness.
This is extra true after a crash type fall. Then once a shock loosened pedal is ridden on, the hard steel of the pedal cuts the aluminum crank threads and you will need new cranks.

The steel inserts in the KH cranks avoid this problem. Greased steel crank threads against hard steel pedal threads is best for hard riding.

The “screw the steel pedal right into the softer alum crank system”, is very popular. It works great in most unis, but isn’t as tough as the KH cranks if you want something to hammer.