Used Hatchet - question on crank and spacers

I bought a used 26 inch Hatchet which seemed to be in very good shape. However, I noticed something odd on the right side where I could feel and hear a thunk (how to describe it?) every few hundred yards when applying hard pedal pressure. Possibly pedal or the crank interface? I decided to check all the bolts (should have done this before riding) and found that the bearing caps were very, very loose. I tightened those up a bit and the problem seems to be gone.

But that I decided to take off the crank to see if there were any other issues. This was the first time I’ve ever taken off a crank arm where it just slid right off after taking out the bolt. The extractor was only needed to get it started. I thought that perhaps the spacer was too big, so I tried a slightly smaller spacer. But when I put the crank back on, I could not tighten the bolt any further than it was originally and this left a gap to the spacer. I put the original spacer and bolt back in.

Is there a problem with this crank interface? Maybe it’s fine, I just wonder about it since it seems different than all my other unicycles. Should I do anything about it?

Sorry to hear this - and of course without seeing the ISIS splines or the hub bearing caps directly I can’t be sure. But it does just sound like things were let to get very loose.

Wouldn’t advice changing the spacer for a smaller one. The size used is the size that should be used and if you tight the crank bolt up good and tight and the crank doesn’t feel loose, touch wood you’re fine.

Main concerns I’d have would be if the former owner rode like this for a while as that could ruin your hub’s splines and the bearings the could also be shot if subjected to poor installation etc.

But if when all is tighter up as it should and you feel a zero creak and steady ride I’d say not too much else needs doing.

Just monitor it for the next few rides and see if things loosen. They shouldn’t but if they do then you may need to get back here with photos so we can help diagnose other remedies.

Hope this helps a bit!

There is a couple of things I’d try:

  • Put the thinner spacer in and torque up the bolt, then, using the original spacer like a feeler gauge (with the wheel out), see if the gap is smaller than it was. If it is you might need a spacer which is in between the sizes you have. If you have a set of calipers you could always measure the gap when you have the crank tightened up.
  • If you suspect the crank is worn try fitting the one from the other side to see how far it goes on (you don’t want to run it on that side but it would let you see if there is a big difference on how far they seat).

From what you say the crank is probably fine and the spacer is ever so slightly too thick such that there isn’t a tight fit on the taper. As far as I understand, it is supposed to bottom out on the spacer and not really rely on the taper to stop it.

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The standard instruction for determining the required spacer thickness is to push the crank on by hand and then select a spacer about 3 to 5mm less then the space from the bearing to the crank. With the correct spacer the crank will fit tight on the tapered ISIS spline and against the bearing when the attaching crank bolt is tightened.
Here is a video that calls for 2mm space but the official ISIS spec is 3 to 5mm preload that is specified by the crank manufacturer.

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Well, that’s what I can’t do. Once I push the crank on, that’s it. Tightening the bolt doesn’t move it, or perhaps it is a very, very small amount. Something doesn’t seem right. I do have some other cranks sitting around. Next time I take the crank off, I’ll see how one of the other cranks fit. That might give a clue. Right now, though, I’m tempted to leave well enough alone and worry about it in the future if it starts to misbehave. Or should I try to figure it out now before it potentially gets worse?

If it were my unicycle, I think I’d just want to do a full inspection of both cranks and axle splines. Meaning you’d take off both cranks. Check the splines within them and on the hub’s axle and compare the “look” - also take photos for extra backup. Also: double check how the axle bolt is threaded and entering the axle itself. Just to make sure nothing is cross threaded or in need of a clean.

Then I’d mount them as if they were a brand new set of cranks and compare how they seat and tighten - as in does one fit better or require more turns to tighten.

If they both tighten to near the same level I’d be pretty happy and just ride it for a good bit and monitor it.

If you do see a differences in the crank’s splines “socket” you may need to replace with newer cranks - and if the hub’s splines looked messed up on the right side compared to the left - this would be worst case scenario as the hub would have an issue. However you could follow the suggestions above regarding using smaller spacers on the right and perhaps even get it mounted via a bike shop with a torque wrench to apply a bit more force to it than one might be able to at home.

These are just suggestions on how I might approach this but of course the adage. If it ain’t broke, don’t fix it - could be a good one to follow here and only do the above if you notice issues in the next ride or two.

Sounds like you sorted the problem when you tightened the bearing housing. I wouldn’t worry about the cranks if they’re not making any noise or wobbling.

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Is this a hatchet with a steel hub, or an aluminium hub?

If it’s a steel hub, then it sounds like the crank interface is worn (although why this is the case if it has spacers installed I don’t know) and it’ll get a little worse over time but it’s unlikely to do too much to the hub itself if the cranks aren’t moving now when tight. You’ll need new cranks though, either now or later.
If it’s an aluminium hub then the interface on the hub itself may well be quite worn, which is obviously rather more work to replace.

Before putting the crank bolt in, is the end of the crank that the bolt pulls on obviously in-line with the end of the axle?

I did think that cranks that had very little clearance between where the bolt presses on it, and the end of the hub were very much a thing of the past though so I’m surprised that you don’t seem to be able to just switch to a smaller spacer. Interface wear isn’t a new thing and something like my KH Spirits can easily cope with 3mm or so more than their initial loaded position before they’re junk.
Perhaps this is down to trying to get to a narrower q-factor?

Just chiming in on the aluminium verse steel axle.

I had this debate over what version my Nimbus Oregon was as I couldn’t find a definitive answer at that time from UDC.

My way to make sure what type I had was to test axle with a magnet. The magnet attached which told me I had the steel version as aluminium wouldn’t react this way.

I am personally a bit puzzled why any Oregon / Hatchet would come with the aluminium hub as this feels a bit counterintuitive for the type of unicycle the hub is being installed in.

Anyway - just a tip in case like me you find it really hard to determine your hub’s version.