Coker Big One - Hub & Bolt question.

Can someone advise me please?

I’ve just waited three months for another coker big one 36" (Original model) after the hub on mine twisted after two uses.

I’ve just received it and I open up the crank nut cap to tighten and I was faced with some of the worst bodgy engineering I have ever seen.

The pictures explain it better than words can but on my first big one first pic) there is a standard cotterless crank square taper with a nut that screws on the thread. Standard stuff, you’d think.

On the replacement from Coker (second pic) it’s a square taper cotterless crank with a Bolt screwed into the Hub and holding the crank on. No washers, no bolt face just shoddy looking engineering.

My questions, before I mail this to Coker, are Has anyone else seen this on a Coker big one? Is it a very old model?

Any suggestions? Am I just being too fussy?

All help appreciated…


It’s normal, and actually an improvement - bolted hubs are newer and better at holding cranks on / not stripping, which hubs with nuts tended to do. The hubs all went this way (before they all went splined).


The first one is an older design you hardly ever see any more except on really cheap stuff. All (decent quality) square taper hubs (and bike bottom brackets) have used the second method for a long time. The old type with the nut is much more prone to stripping threads and most manufacturers changed to the bolt type.

It’s also quite normal to use a flanged bolt instead of a separate washer. (although on second thoughts that one in your picture does look like a normal bolt, which ought to have a washer)


EDIT: Joe beat me to it.

Oh, but bolted hubs I’ve seen have a fancy bolt with an allen key head. I don’t know if that makes a difference.


Old CrMo hub has the same design and never failed for me (on my hockey unicycle, a Nimbus X)

Joe & Rob, [Edit] & Marco

Thanks for the replies I was just packing it into the box to send back.

I’ll get a plain and spring washer on there and all should be ok then hopefully.

I was just a bit horrified by the fact that it was only clamping the crank onto the taper by 4 small parts of the crank which are also getting chewed away everytime you tighten them up.

Here’s hoping the hub doesn’t twist on this one after two rides!!!

Cheers for the help fellas! Much appreciated. Thanks for being there.

That should help - they really should have put one in, or used a flanged bolt. It’s more normal with the bolt-type axles to use bolts with a flanged head (similar to the nut in your first picture) rather than a normal bolt, so it doesn’t need the washer. Most of the newer ones now use allen-key bolts that often have a built-in captive washer.

If you use a spring washer as well, make sure you’ve still got a decent amount of bolt thread in the axle. It’s more usual to have just a plain washer on there, and possibly a dab of thread lock to stop it coming loose. You need to do the bolts up really tight on unicycle sq-taper hubs (30lbft or so) - they come loose more easily than on bikes.


I wouldn’t use a spring washer. A flat washer will do fine. If you use thread locker use the blue, not the green, or red. The blue will be much easier to release later when you need to remove the cranks.

Shoddy is right, Coker sent you the wrong bolts. Crank bolts need a washer, or incorporate the washer surface. I suggest you call Coker and ask them to send you the actual crank bolts. I own a Big One, and those bolts fom Coker incorporate the washer.

Yeah, crank bolts are better than nuts, and I wouldn’t use a spring washer, just a flat washer.

For what it’s worth, I like crank bolts that are don’t have teeth on the washer surface, so they don’t remove crank material each time they are tightened. My experience is that the smooth surface crank bolts stay tight just as well as the toothed ones.

edit: I just noticed yours is a steel Big One, not the Aluminum model (mine). So maybe things are different between models. I still think they sent the wrong bolts.

A better option may be to replace them with these. The bolts Coker sent you should really look like this, with the round bit at the bottom of the bolt.
I suggest you direct your contact at Coker to this thread and explain the situation, rather than send everything back. If you got it directly from Coker in the USA the shipping costs will be huge, if you got it from their old importer in Hampshire they won’t know anything about unicycles (they’re a car tyre importer).

You may want to do things simply and order a pair of the crank bolts from No washers needed and you’ll be fine as these are used on at least 5 of my unicycles. it’ll cost you a tiny bit more, but compared to the money and time you’ve spent already then it’s nothing: and if you order it today you could be riding without a worry tomorrow!

You guys are awesome!
Thanks for the advice. I’ll ask Coker to send me a couple of bolts and I may even order some from UDC next time I put an order in.
I’ve got a plain steel washer under it now and it seems fine. I’m gonna take it to the local cycle track at the weekend to see how it rides!
Thanks to all those who replied, this is a great community to be a part of!


You should be fine with a plain washer, but if Coker is going to send you something you might as well request the proper bolts. Methinks maybe they ran out of them or something when yours was shipped, and maybe they didn’t want to keep you waiting any longer. I hope.

I usually give my square-taper unicycles a little check with the crank wrench before each ride; by doing that I haven’t had my cranks come loose in many years, even with Coker MUni and lots of other abusive activities.

It may be a crank bolt that they sent. I think that they just had an old style of crank bolt and forgot to put the washer in (or didn’t have a washer because the newer style bolts don’t need them).