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I have a road bike with ISIS splined cranks. I've been noticing front derailleur rub lately, and when I took a look, both of my crank arms are wobbly. The retaining nut is very tight, so tight on the drive side that I can't even back it out.

The bike is an entry level bike equipped with Shimano Sora. Except for the crankset, which is an alloy crank from (Taiwan).

I checked the BB by seeing whether the wobble transmits to the other side, or to the crank axle. It does not. Each crank independently wobbles. From what I've read, this implies that the crank splines are worn.

I am thinking the most conservative move is to replace the cranks and see what happens. The most aggressive repair is to replace the entire crankset, including BB and chain rings.

Are there any options that I have missed?

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  • I'd first take the crank arms off and make sure that there isn't some sort of foreign material in there or some such. And make sure the bolts are not over-long such that they are bottoming out in the threaded holes.
    – Daniel R Hicks
    Aug 4, 2016 at 1:09
  • I too have wondered if the bolts are too long. I asked customer support if there is a washer that was forgotten during manufacturing, but they said there are no washers. I find it hard to believe that a high torque bolt like this one has no washers, but... Anyway, I need to buy a allen socket to back these bolts out.
    – nogasbiker
    Aug 10, 2016 at 16:40
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    I bought the right tools and checked the bolt length. Even without a crank, the bolt doesn't bottom out in the BB. So the bolt is fine. It did not prevent the crank from seating fully in the BB.
    – nogasbiker
    Aug 12, 2016 at 20:38

3 Answers 3

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Sounds like wear between cranks and bottom bracket. Strange its the same on both sides, I'd expect your primary foot side to be more worn.

Have a good look at the interface between crank and BB. Look for wear and witness marks to see if they're worn together or just the BB or just the cranks are worn.

You shouldn't have to change your chainrings unless they're a one-piece unit with the right-hand crank.

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  • I was hoping to get through the riding season as it is, but I guess loose cranks are bad for the spindle interface. I'm going to try and repair this, but at the first sign of hassle, I intend to switch to a two piece crank. The ISIS system bugs me, in that the retaining bolt is torqued to 40 ft-lbs. Can't remove and/or retorque that on the road with a mini toolkit. The two piece systems I've seen have a clamp mechanism, where it uses two small bolts torqued much less. I guess the market has spoken on ISIS spindles- they've largely disappeared. I can see why...
    – nogasbiker
    Aug 10, 2016 at 16:43
  • @nogasbiker you could simply wear it out by riding it till it breaks, but what if you're standing on the pedals at that moment?
    – Criggie ♦
    Aug 10, 2016 at 21:17
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    As you posited, it is just plain old wear on the spline interface. The BB itself looks fine, just wear on the crank splines. I have 1,500 miles on the bike; hard to imagine that I'd have to change cranks at such a "low" mileage. I've already ordered a Shimano Hollowtech2 crankset. Adios ISIS.
    – nogasbiker
    Aug 12, 2016 at 20:39
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I have owned a similar ISIS splined crankset made by Truvative, and had a similar experience. The problem, I believe, is the interface between the hard steel of the bottom bracket, and the soft, light aluminum alloy of the crank arms; once you crank them down there's no way to keep the arms from wearing out. I ride approximately 25 miles per day, and the cranks were worn out in a week. My advice would be this: toss them, and get something more durable. I found a pair of Specialized S Works cranks and bottom bracket for $6,00 at the local bike co-op and have been extremely happy with them. Good luck.

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  • "Specialized S Works cranks and bottom bracket for $6,00 at the local bike co-op" Nice. Easy on the budget, reuse something. Keeps stuff out of the landfills. But don't Specialized S Works cranks use BB30 bottom bracket? I would think that a frame that had ISIS in it wouldn't be able to run a BB30 bottom bracket.
    – nogasbiker
    Aug 20, 2016 at 2:11
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Ok, I bought the tools needed to break loose the retaining bolts on the ISIS cranks. The problem is that the aluminum splines on the cranks were worn / out of shape. Instead of a nice cylindrical shape, they were flattened.

I'm somewhat disappointed in the ISIS spline system for a couple of reasons:

1) minimal surface area to retain crank. The bolt basically holds the ends of the crank spline flush with the receiving BB splines. So if the tiny aluminum ends on the crank deform, the whole interface will start moving around. 2) retaining bolt needs to be torqued to around 35 ft lbs. That is more than I can muster on the road with a mini toolkit, if a bolt were to loosen. Meh, I'd rather have the two 7 ft lb bolts that modern cranksets use.

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Thanks for the advice. I've ordered a Shimano Hollowtech crankset and will get rid of the ISIS stuff. Unfortunately, I still have to buy the ISIS BB tool, even though I will use it exactly one time ;)

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Update

I installed the new crankset (Shimano Sora), chain (SRAM PC-991), and BB (Shimano Ultegra Hollowtech). I've been riding on it for a year now. Derailleur chain rub is gone, drivetrain action is very smooth and quiet. The crankset is very solid, and now I can confidently stand on the pedals when needed. Cost about one hundred bucks total, and an hour or two to install.

Thanks for the advice and help.

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  • Will do. I'm a newbie to stackexchange :)
    – nogasbiker
    Dec 11, 2017 at 20:04

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