When Aluminum crank square hole get enlarged.

Because I’ve been switching cranks often on my 36er, going from 127mm, to 102’s, then to 152’s (for coker MUni), the aluminum cranks (the 127’s) have become enlarged where they fit onto the square taper axle, to the point where, when the bolt is fully snugged down, the bottom of the crank was almost touching the bearing holder. :astonished:

The steel cranks don’t have this problem at all.
So I took some aluminum tape and put a couple pieces on each axle to “thicken” it a bit, then carefully placed each aluminum crank on over the shimmed axle. (The cranks still fit quite easily onto the very beginning of the tapered axle even with the added tape)

It seems to have worked like a charm and when fully tightened down, they are now several mm further away from the bearing holders. Just thought I’d pass this on if anyone else had this problem.:smiley:

I have some Aluminum bike cranks… I slightly twisted one while bunny hopping down a 3 set of stairs… still very ridable.

I definitely would not want to be removing and replacing these cranks very often… they’re so light even for 170mm cranks…

The left crank weighs less than my half used stick of deodorant pretty much…

If I ever get a Coker, I’ll machine the spider off of the right crank and use them for getting used to the big wheel.

I avoid aluminum cranks like the plague. Every time I’ve ridden with them, I’ve ended up with a catastrophic failure… miles from the nearest trailhead. Never fun.

While shimming might be a good “limp home” fix, I don’t see it as something that would be trustworthy long term. If I were you, I’d look for bits of aluminum tape falling out of the crank end sooner than later. Aluminum tape isn’t made for any sort of structural application.

How long have you ridden the Coker with your fix? If I were you, I’d toss those aluminum cranks before they leave you stranded…

I think Maestro’s being a bit over dramatic. Obviously if you’re doing a lot of crank swapping then ally cranks will wear out faster than steel ones, but when they’re fitted I don’t reckon they’re any less reliable than steel - in fact the only time I’ve had a crank come loose on a ride it was a steel one on my coker. I’ve had ally cranks (prowheel 150s) on my muni for three years with no problems - just fitted them, torqued the bolts up and never had to touch them until I took them off to fit new ones a couple of weeks ago.

The only downside I can see to aluminium square-taper cranks (apart from the wear with repeated refitting) is if you’re doing really extreme stuff then ally will tend to crack rather than bend if it fails, and it’s easier to limp home on a bent crank than a snapped one. Most of my riding is more cross-country (although sometimes pretty rocky) rather than big hops and drops so it’s not been a problem for me. Having said that, the reason I replaced those three-year-old prowheels recently is because they started to develop hairline cracks, but that was after a good few thousand miles of riding.

If Terry is swapping cranks that often perhaps he’d be better off using a splined hub - although most of the new hubs are ISIS which is still a tapered axle so presumably suffers from the same wear problems as square-taper after multiple refits. I’ve never had anything with ISIS cranks - are they any better in this respect than square-taper?


Ok, just for the sake of playing ‘devils advocate’ here, but would alimunium cranks be better for a regular crank-swapper than steel?

Each time you swap steel cranks on a steel taper hub, you are still going to be wearing away a little bit of metal. Ok, no where near as much as with ali, but it will slowly wear away. But with an ali crank, the weak spot is the ali, so that will go first. With a steel crank, it’s both the crank AND the hub equally.

So, whilst you will have to look at ali cranks being replaced fairly often, at least the hub will last longer.



Isn’t the axle made of hardened steel?

Ah, but replacing cranks is much easier and cheaper than replacing the hub :slight_smile:
I’d rather pay £10 for a pair of cranks every couple of years than £30 for a hub and have to rebuild the wheel. Depends how often you swap them (and therefore how long they last) I s’pose.


Yes, I would hope it’s significantly harder than cheap steel cranks.


Yeah, that was the point I was (badly) trying to make :slight_smile:


Porbebly not as bad as you make it out though, but it is still true.

a short term fix i have used where the crank and/or shaft are misshapen is plumbers PTFE thread sealing tape.

Well if you’re going to go that route, why not save your money and stuff some toilet tissue in the crank before mounting it? It’ll probably work just as well… :roll_eyes:

I used newspaper on my Norco. Worked amazing actually… I highly doubted it would even work.

Eventually I just did a plug weld to permanently attach the annoying cranks.

All grades of aluminum alloys are not the same. Some are softer than others or have other properties that may cause the taper to deform more easily. Other grades of aluminum alloys may hold up better.

The Kooka cranks are made from a sturdy flavour of aluminium. I believe Kooka used 7075 T6 alloy. The Kookas will hold up to repeated crank changings better than your run of the mill aluminum cranks.

So finding well machined cranks made with a suitable alloy that is properly heat treated and properly finished is the trick. Unfortunately square taper cranks like that suitable for unicycling are a rarity and expensive.

The aluminum ISIS cranks are going to hold up better than the same type of square taper alloy crank. Even though the ISIS is tapered the taper faces don’t get the same wear and abuse as the square taper designs do. The trend of unicycles (including freestyle and touring style) moving to the ISIS system is a good thing. If you’re going to be a frequent crank changer I’d rather have an ISIS system than the square taper system.

10 years from now we’re going to look back at square taper unicycle cranks in the same way we now look at cottered cranks. ISIS is the future.

The KH Moment cranks are strong as hell, and aluminum. There is a steel “sleeve” fitting for the pedals to screw into, but the splined axle opening is not sleeved; just aluminum.

While the discussion is on effect of frequent changing on the crank holes, I would think there has to be a long-term effect on the hub as well. I put my tri-tapped Kooka cranks on my coker over 2,000 miles ago, and haven’t had to change or tighten them since. I still change my crank length all the time…by changing my pedals, which is a much faster, less-impactful process.

Terry, I know you don’t like “the Q”, but I’d recommend you give this solution some consideration. There may be other cranks with less Q that would still work well for the multiple drillings. I’m not sure. I just know that the tri-tapped cranks have been a game-changer for me, as I can now adjust my unicycle during the ride, which really helps. The longer your rides get, the more variation in terrain you have the chance to encounter.