Yooper's broken Coker bolt


I finally tested the hardness of your broken bolt today. It tested at 66 RB. A comparable size grade 5 bolt checked at 102 RB. I didn’t have any lower grade bolts to check.

The bolt head has three points of heavy contact on the underneath surface. One on each side of the ‘tooth’ and one opposite of it.

The bolt had a area where the head intersects the shank with a zero radius. This is probably where the tear started.

At this same point there was a very minute amount of oxide. The tear may have been there for a while, but it wouldn’t have been more than a couple of thousandths deep. The bolt head probably failed all at once since it doesn’t show any cyclic tearing.

There is a spiral scratch/groove on the shank just above the threads that doesn’t match up with any features on the Coker. This damage could have happened after the break as you were flying through the night air.

The threads where the nut was engaged shows that they were under a very heavy load while the nut was turning (heavy grooves).

I think the bolt was over-torqued at some point, even though that may have been before you came into its life. The Coker bearing retainer puts some bending into the bolt due to poor support, so it may not have taken much remaining torque to get the head to pop off. I’m going to start looking for replacement bolts for my Coker tomorrow.

Personally, I think you were doing some new high tech routine at night so you could spring it on everyone at the next event. If you continue to deny this we will be forced to get the operator of the Harper I.V spy satellite to focus its IR camera at your neighborhood. :slight_smile:

If you find some, especially some stainless steel with the same round head with the tab, please let us know. Along with my Coker spokes, those bolts have really taken a corrosion hit. I’d really appreciate it!

Otherwise, I’ll look for some without the tab, which appears to be more of a convenience than a necessity.

I tried to send you an e-mail, but it bounced back. If you have a new address please let me know.


Thanks for going to the trouble of doing such a thorough test. When I bought a unicycle at a LBS all of the maincap bearings on the display models were so over-torqued that the wheels wouldn’t turn freely. If the bolts aren’t in a package when you receive the unicycle you can probably assume that they have been abused like this. There are perhaps as many ignorant unicycle assemblers as there are savvy unicycle riders. For the PC among you, please note the vast difference between ignorant and stupid.

Thanks for the writeup.

Re: Yooper’s broken Coker bolt

“Cokerhead” <Cokerhead.efe5n@timelimit.unicyclist.com> wrote in message
> Doug,
> I tried to send you an e-mail, but it bounced back. If you have a new
> address please let me know.
> -Mark

Hi, Mark,

it’s : dvm2 at cox.net