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ISIS crank question

Old 01-22-22, 01:48 PM
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Plainsman
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ISIS crank question

I know you are supposed to lightly grease the splines on an ISIS BB spindle. I’ve read that you don’t want any grease on the mating surfaces between the contact face of the crank arm and the crank bolt though. Is that true? Do you still lightly grease the threads of the crank bolt?
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Old 01-22-22, 03:09 PM
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I have a bike with an ISIS BB spindle. I lightly grease all the surfaces you listed. Grease on the mating surfaces between the crank arm and its fixing bolt will not cause a problem as long as the bolt is properly torqued; in fact it prevents the bolt from being under-torqued.
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Old 01-22-22, 03:34 PM
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Where there any cautions about it in your installation instructions? If not, don't worry.
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Old 01-22-22, 03:38 PM
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Originally Posted by sweeks View Post
I have a bike with an ISIS BB spindle. I lightly grease all the surfaces you listed. Grease on the mating surfaces between the crank arm and its fixing bolt will not cause a problem as long as the bolt is properly torqued; in fact it prevents the bolt from being under-torqued.
Thank You!
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Old 01-22-22, 04:37 PM
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Grease everything.
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Old 01-22-22, 06:18 PM
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Another vote for grease it. Can't hurt and enough leeway in torque precision to not worry about it.
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Old 01-22-22, 06:52 PM
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I grease all the things on ISIS stuff, how much depends on the fit though. They can vary a lot in how tight they fit depending on brand/wear. If it's super loose I'll barely grease the splines.
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Old 01-23-22, 09:56 AM
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Grease it. An argument can be made that tapered spindles shouldn’t be greased to prevent overtightening the bolt and pushing the crank too far onto the spindle. That can result in cracking the crank. It’s not a strong argument and, if you take care during assembly, will almost never happen.

ISIS cranks aren’t tapered and have a built in stop. The crank can’t be pushed on hard enough to crack the crank. Grease makes it easier to remove the crank in the future. That holds true for tapered cranks as well.
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Old 01-23-22, 09:14 PM
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Originally Posted by cxwrench View Post
Grease everything.
https://dreambuildstore.com/shop/p/u...the-grease-tee

Also I would treat any metal on metal like Groundskeeper Willie chasing dogs:

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Old 01-24-22, 06:24 PM
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Originally Posted by cyccommute View Post
ISIS cranks aren’t tapered
Incorrect, the splines are in fact slightly tapered, see the engineering drawings.

and have a built in stop
There is indeed a stop, but it's often a separate spacer piece which can be changed out to achieve a particular fit. In theory, repeated re-fitting would need progressively smaller spacers to be tight on the tapered splines.
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Old 01-24-22, 06:50 PM
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Originally Posted by UniChris View Post
Incorrect, the splines are in fact slightly tapered, see the engineering drawings.



There is indeed a stop, but it's often a separate spacer piece which can be changed out to achieve a particular fit. In theory, repeated re-fitting would need progressively smaller spacers to be tight on the tapered splines.
According to ISIS Drive FAQ

inThe entire ISIS Drive system is based on the crank stops of the spindle. Everything in the standard is derived from these crank stop “datum planes”, including the method of measuring a spindle. Since the spline shape itself is defined relative to these stops and the taper angle is so small on the flutes, the cranks should easily slide all the way onto the spindle until they are stopped by these crank stops. Thus these crank stops consistently locate the crankarms axially relative to the bottom bracket (and hence the frame) every time a crank is installed. The overall length of the spindle has no effect on the axial position of the crank on the spindle, and thus has no meaning in the context of this standard.a spindle. Since the spline shape itself is defined relative to these stops and the taper angle is so small on the flutes, the cranks should easily slide all the way onto the spindle until they are stopped by these crank stops. Thus these crank stops consistently locate the crankarms axially relative to the bottom bracket (and hence the frame) every time a crank is installed. The overall length of the spindle has no effect on the axial position of the crank on the spindle, and thus has no meaning in the context of this standard.measuring a spindle. Since the spline shape itself is defined relative to these stops and the taper angle is so small on the flutes, the cranks should easily slide all the way onto the spindle until they are stopped by these crank stops. Thus these crank stops consistently locate the crankarms axially relative to the bottom bracket (and hence the frame) every time a crank is installed. The overall length of the spindle has no effect on the axial position of the crank on the spindle, and thus has no meaning in the context of this standard.g
They also state a bit further on in the site that the taper is 1%
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Old 01-24-22, 06:57 PM
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Indeed, you've quoted them explicitly saying there's a taper.

It also happens to be well understood among heavy users of that standard, that highly repeated re-mounting requires shortening the stops.

Having the crank stop on the stop while the tapered spline is still loose is a thing that actually happens, and with negative results.

It is what any student of mechanically engineering would readily identify as an "overconstrained system" - it works, but only with a narrow band of tolerances, a band that can fortunately be moved by changing the stop.

In contrast, an untapered system would pretty much not work at all, or at least not be able to be assembled.

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Old 01-25-22, 09:50 AM
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Originally Posted by UniChris View Post
Indeed, you've quoted them explicitly saying there's a taper.
I’ll grant that I was incorrect on saying that the ISIS aren’t tapered. However, the taper is very minor compared to the taper of a square taper. They do have a stop that keeps them from creeping up the spindle like a square taper does when the bolt is over tightened on a square taper which can result in cracking of a square taper crank.

It also happens to be well understood among heavy users of that standard, that highly repeated re-mounting requires shortening the stops.
How would repeated re-mounting shorten the stops? Repeated remounting should lengthen the stop because it (might) cause expansion of the bore. That would allow the crank to move further up the shaft and result in a looser fit.

Having the crank stop on the stop while the tapered spline is still loose is a thing that actually happens, and with negative results.
I agree that having the crank bottom out before it is tight would not be a good thing, however I’ve never had a ISIS crank have a problem with loosening in use nor have I ever experienced fit problems and I have used them extensively. I have two bikes with ISIS cranks from the 90s that are still going strong.

Nor have I ever seen any kind of spacer on any bottom bracket I’ve ever used. Nor have I seen any kind of spacer on hundreds of these kinds of cranks I’ve taken apart at my local co-op. Nor have I see any spare spacers running around in the mountains of various small bike parts I’ve sorted at said co-op. I’ve sorted several tons of nuts, bolts, washers, spacers, nonbike parts, and even the occasional bullet but I’ve never seen a spacer that has that very distinctive pattern of a splined bottom bracket.

It is what any student of mechanically engineering would readily identify as an "overconstrained system" - it works, but only with a narrow band of tolerances, a band that can fortunately be moved by changing the stop.
As I said above. I’ve never seen any kind of spacer for an ISIS bottom bracket. The exploded view of an SKF bottom bracket shows no spacers of any kind on the splined part of the spindle. The ends of the splines milled into the spindle are visible after installation and aren’t covered by a spacer. Cranks don’t come with spacers either.
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Old 01-25-22, 10:37 AM
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Originally Posted by cyccommute View Post
How would repeated re-mounting shorten the stops? Repeated remounting should lengthen the stop because it (might) cause expansion of the bore. That would allow the crank to move further up the shaft and result in a looser fit.
Which is exactly why what is providing the stop has to then become shorter for the crank to move further up the tapered spline where it can be tight again.

I agree that having the crank bottom out before it is tight would not be a good thing, however I’ve never had a ISIS crank have a problem with loosening in use nor have I ever experienced fit problems and I have used them extensively. I have two bikes with ISIS cranks from the 90s that are still going strong.
Likely because they're rarely re-mounted.

Nor have I ever seen any kind of spacer on any bottom bracket I’ve ever used. Nor have I seen any kind of spacer on hundreds of these kinds of cranks I’ve taken apart at my local co-op. Nor have I see any spare spacers running around in the mountains of various small bike parts I’ve sorted at said co-op. I’ve sorted several tons of nuts, bolts, washers, spacers, nonbike parts, and even the occasional bullet but I’ve never seen a spacer that has that very distinctive pattern of a splined bottom bracket.
At first thought that might be because the place ISIS cranks really caught on - and the place they end up getting remounted more frequently than you're familiar with is not bikes where they're somewhat uncommon... but unicycles where they're considered "the answer" for any sort of rugged usage.

And with one famous exception, they're all supposed to be assembled with spacers, which are sold in a variety of sizes, and sometimes really do have to be changed out for smaller ones when people do things like swap crank lengths, rotate them on the spline rather than rotating the tire on the rim, or to replace cartridge bearings that are pushed more to their limit by sizing constraints.

The spacers don't have a "distinctive pattern" though, they're just rings.

And a search for "isis spacer rings" or "isis crank spacer" will show they're well known on bikes too.

(These are of course distinct from the spacers used for BB width compatibility - those of course exist too and will be intermixed in search results)

Here's a picture of a particularly long one on a trialtech BB - that ring at the left of the image is what forms the crank seating face, and as the manufacturer puts it "Custom silver anodised tapered crank spacers help maintain the correct crank fitment"


Last edited by UniChris; 01-25-22 at 11:46 AM.
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Old 01-26-22, 12:46 AM
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Originally Posted by UniChris View Post
Which is exactly why what is providing the stop has to then become shorter for the crank to move further up the tapered spline where it can be tight again.
Again, I’ve never seen spacers nor can I find spacers that are of different thicknesses for ISIS splines. In 25+ years of using this kind of bottom bracket I’ve never run across any reference to using a spacer. The linked FAQ makes no mention of a spacer. The only mention of a “spacer” I can find is for the cup of the bottom bracket.

Likely because they're rarely re-mounted.
.

You might want to ask before you assume. The cranks have been moved around to numerous bikes. They have been moved from at least 4 different mountain bikes as I changed frames. They have been used on my touring bike, then on my mountain bike and then back to my touring bike. The bottom bracket hasn’t been changed that often because I don’t find bottom brackets to wear out that much but the crank used on my touring bike has had at least 2 different bottom bracket used for it. In 25 years of ownership…these are 5 arm Race Face 94/58 BCD cranks…they have been moved more than a dozen times perhaps not including rebuilds and adjustments.



At first thought that might be because the place ISIS cranks really caught on - and the place they end up getting remounted more frequently than you're familiar with is not bikes where they're somewhat uncommon... but unicycles where they're considered "the answer" for any sort of rugged usage.

And with one famous exception, they're all supposed to be assembled with spacers, which are sold in a variety of sizes, and sometimes really do have to be changed out for smaller ones when people do things like swap crank lengths, rotate them on the spline rather than rotating the tire on the rim, or to replace cartridge bearings that are pushed more to their limit by sizing constraints.

The spacers don't have a "distinctive pattern" though, they're just rings.

And a search for "isis spacer rings" or "isis crank spacer" will show they're well known on bikes too.

(These are of course distinct from the spacers used for BB width compatibility - those of course exist too and will be intermixed in search results)

Here's a picture of a particularly long one on a trialtech BB - that ring at the left of the image is what forms the crank seating face, and as the manufacturer puts it "Custom silver anodised tapered crank spacers help maintain the correct crank fitment"

I’ve used a lot of ISIS bottom brackets. I’ve worked on a lot of ISIS bottom brackets. I’ve sorted a whole lot of ISIS bottom brackets. I have never seen a removable spacer of any kind in a new or used ISIS system. Some have what could be called a spacer but most don’t.

If the crank has the kind of problem you are describing, wouldn’t the bottom bracket need stops on both sides to take fix the problem? The arms are independently installed and will react independently to the torque on each crank bolt. That spacer in the picture serves some purpose but taking up some kind of slack due to expansion of the crank arm bore isn’t it. It makes no sense to be one sided.
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Old 01-26-22, 08:04 AM
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Of course there's one on each side!

Every mention I've made have them, and the manufacturer quote accompanying the picture has been pluaral - spacers.

​​​​​

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Old 01-26-22, 09:59 AM
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Originally Posted by UniChris View Post
Of course there's one on each side!

Every mention I've made have them, and the manufacturer quote accompanying the picture has been pluaral - spacers.

​​​​​
The picture you posted has only a single spacer. Where is the other one?

I’m also having a problem understanding just how this spacer would work. If the bore is expanded because of installation…not something I concede is happening….the spacer would have to be thinner each time the crank is installed to allow the crank to move further up the spindle to take up that expansion. Are you saying that the expansion of the bore is predictable? In other words, if the bore is Xmm in diameter on the first installation, is it X mm + Ymm wider on the second installation? If this were true, the crank fit should get sloppy each time the crank is installed and removed until such time that the crank would be come unusable. And that should happen in fairly short order. A few installations and the crank should be discarded even if you changed the spacer.

If the bore expansion isn’t predictable, i.e. a random event, the spacer would need to be either trimmed to fit or would need to be available in thousands of sizes. Trying to decide which one of those thousands of spacers you’d need would be trial and error. And just installing the crank would require a different spacer.

If you want to do dueling pictures, here’s an exploded view of the SKF bottom bracket offered by Rene Herse Cycles




There are no spacers on the shaft in that picture. If you go to the website, there is a picture of the bottom bracket with no spacer on the spindle shaft.
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Old 01-26-22, 10:09 AM
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I've never used ISIS, but my guess about the spacer would be that if ISIS doesn't require full engagement of the cranks, then the spacer might be used on wider BB shells to keep the crank arm from rubbing the shell. Though why not just get a BB with wider longer spindle.

I doubt the spacers were because removing and re-installing crank arms on ISIS causes them to sit more lower or inward on the spindle. If one would publish the link to the documentation of the ISIS with claimed spacers, then maybe this could be resolved instead of all this imagining as I did myself.
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Old 01-26-22, 10:45 AM
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The effort you are putting into denying an aspect of reality simply because it's outside your personal experience is getting rather absurd.

Originally Posted by cyccommute View Post
The picture you posted has only a single spacer. Where is the other one?
Inside the other bearing cap, or not yet installed. Given that we can see the relief at the start of the splines which it would appear to cover when installed, presumably not yet installed.

But don't take my word that it exists, here's a picture of the same BB with both spacers clearly visible. I chose the picture I originally did because it clearly showed one removed as a loose part.


I’m also having a problem understanding just how this spacer would work. If the bore is expanded because of installation…not something I concede is happening….the spacer would have to be thinner each time the crank is installed to allow the crank to move further up the spindle to take up that expansion.
Quite simple: if the fit of the crank is found to be still loose on the splines when against the spacer (typically evidencing itself as a creaking sound) then the spacer is either machined down or replaced with a shorter one.

the spacer would need to be either trimmed to fit or would need to be available in thousands of sizes
Given the taper is quite slight, 1 mm steps seem to work in practice, since a fairly large linear displacement makes a tiny change in radial fit.

But they're also pretty readily altered - I know people who've made custom ones from offcuts of seatpost, tuning with a file. Personally I'd use my little toy lathe (not because I need to make an adjustment, but because I simply lost one of original spacer rings for a combination I'm not riding right now anyway)

If you want to do dueling pictures, here’s an exploded view of the SKF bottom bracket




Your picture also shows that the crank seating faces are removable spacers. Only in this case they're distinctly shaped on each side as your BB is on the whole less symmetric than the example I chose, and since those are serviceable rather than sealed cartridge bearings, there's also a ring carrying a bearing seal inboard of each removable seating face / spacer.

Can you make an ISIS spindle with an integrally machined seating face? I can accept that your experience says yes, though that's not actually the case in the picture you chose to post.

Can you make one with a removable and alterable spacer as the seating face? Those are the type I'm most familiar with, and I've just shown you a picture of one.

Ultimately this comes down to the question: is it better to make something that fits only under a narrow range of conditions, but usually "just works" within them?

Or is it better to make something where the fit can but customized to perfection for the reality of a given combination of parts?

My suspicion is that for some "ordinary" bike uses the first may get chosen (although integral machining would seem to require rather large bearing bore) but for high crank stress applications like trials bikes and unicycles, the second is chosen.

But with your picture choice, we're also seeing that the removable spacers can be present even when not recognized for what they are.

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Old 01-26-22, 10:58 AM
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Originally Posted by Iride01 View Post
my guess about the spacer would be that if ISIS doesn't require full engagement of the cranks
On the contrary it absolutely does require full engagement of the splines - for any given real world example of a crank and a spindle, there's one axial position where that crank "fits".

then the spacer might be used on wider BB shells to keep the crank arm from rubbing the shell. Though why not just get a BB with wider longer spindle.
No, that wouldn't work at all. You can use a different sort of spacer on the bearings to very slightly alter what size BB shell some of them fit in, but to increase the spacing between the cranks you absolutely need a longer spindle such that the cranks are tight on the tapered splines at a workable width. Of course clearance wise many cranks also have some "Q" offset of their own, a lot of it concentrated towards the spline end.

The reason for adjustable crank fit spacers is to make it so that the tapers can be perfectly tight in a given mating of actual parts. As I was pointing out earlier, a crank seating face fixed in position to the taper is what mechanical engineers call an "overconstrained system" and something they habitually try to avoid - bottoming out on the seating face, and being material-springiness-range tight on the tapered splines have to perfectly coincide. Because they don't want the crank "walking" up the taper the seating face is usually considered essential - we accept that an overconstrained system is unavoidable - but if you want it to be a truly self-consistent overconstrained system, then in reality you make it an adjustable one.

To make a crank/spindle interface that's not overconstrained you either have to use a taper alone (say classic cotterless square taper, with all their various issues), or use a non-tapered spline that instead uses a pinch bolt to allow enough clearance that it can be assembled - or go back to the ancient cottered crank idea. I'd argue the pinch bolt clampled splines idea is in a way the cottered idea updated to the modern age with its weaknesses removed. I just wish there weren't so many incompatible versions of it.

Last edited by UniChris; 01-26-22 at 11:12 AM.
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Old 01-26-22, 11:29 AM
  #21  
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Seems like maybe you are arguing about something that doesn't happen on all ISSIS BB's because of there appear to be different ways of controlling how the cranks sit on them.

Some seem to have a spacer that may or may not even be a removable part for the cranks to bottom on while others seem to intend for the crankarm to bottom on the end of the spindle.
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Old 01-26-22, 11:36 AM
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Originally Posted by Iride01 View Post
while others seem to intend for the crankarm to bottom on the end of the spindle.
Absolutely definitely not. The outside edge of the crank bore is actually relieved to make the seating face of the crank bolt, there's no inward facing "shelf" there that could serve as a stop on the end of the spindle.

Besides, having one would make the usual crank spline manufacturing technique of broaching impossible.

If you take the crank bolt out of an ISIS setup you can see essentially the entire end of the spindle, diminished only to an imperceptible degree by the remaining bit of crank spline taper beyond its fitted position.

An ISIS crank either seats against an inboard face (per the standard) or relies on the taper alone (not recommended, though I do have one uniquely famous example)
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Old 01-26-22, 12:08 PM
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Sounds like a mess then. I just stick with octalink or hollowtech II. One and only one position the crank arms can sit on the spindle when properly installed.
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Old 01-27-22, 10:47 AM
  #24  
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Originally Posted by UniChris View Post
The effort you are putting into denying an aspect of reality simply because it's outside your personal experience is getting rather absurd.
Oh, there is absurdity here but it’s not coming from where you think it’s coming from.

Inside the other bearing cap, or not yet installed. Given that we can see the relief at the start of the splines which it would appear to cover when installed, presumably not yet installed.

But don't take my word that it exists, here's a picture of the same BB with both spacers clearly visible. I chose the picture I originally did because it clearly showed one removed as a loose part.

It’s not the “spacer” I’m objecting to. It’s the idea that the spacer is somehow changeable to adjust for this mythic wear you keep talking about. The ISIS has a stop on the spindle as I said long ago. Some of the stops are machined into the spindle and some are a press fit spacer. Square tape doesn’t have that stop. The idea that the spacer needs to be “adjusted” to ensure proper fit is what is the absurd bit.

Quite simple: if the fit of the crank is found to be still loose on the splines when against the spacer (typically evidencing itself as a creaking sound) then the spacer is either machined down or replaced with a shorter one.
A lathe is something that every bike shop and home shop has, right? Again, how much does the fit change each time the crank is removed and replaced? Is it predictable? Would putting the crank on, finding it not fitting quite properly, removing it, machining down the spacer, and reinstalling it change the measurement each time it is reinstalled?

Given the taper is quite slight, 1 mm steps seem to work in practice, since a fairly large linear displacement makes a tiny change in radial fit.
A 1mm step would be huge even with a slight taper…not that the bore changes much with each installation. Square taper changes more with installation and it doesn’t change much at all.

But they're also pretty readily altered - I know people who've made custom ones from offcuts of seatpost, tuning with a file. Personally I'd use my little toy lathe (not because I need to make an adjustment, but because I simply lost one of original spacer rings for a combination I'm not riding right now anyway)
That assumes you can get the “spacer” (the stop is closer to the correct description) off the spindle. If the “spacer” were meant to be removed and replaced with a shorter “spacer”, why doesn’t the Trial-Bikes offer “spacers” of different sizes?

Your picture also shows that the crank seating faces are removable spacers. Only in this case they're distinctly shaped on each side as your BB is on the whole less symmetric than the example I chose, and since those are serviceable rather than sealed cartridge bearings, there's also a ring carrying a bearing seal inboard of each removable seating face / spacer.
It shows a removable stop. They don’t offer this stop in different thicknesses if the stop is meant to be used for the crank fit. That stop would also be a whole lot harder to machine at home if it were used for the crank fit.

Can you make an ISIS spindle with an integrally machined seating face? I can accept that your experience says yes, though that's not actually the case in the picture you chose to post.

Ultimately this comes down to the question: is it better to make something that fits only under a narrow range of conditions, but usually "just works" within them?

Or is it better to make something where the fit can but customized to perfection for the reality of a given combination of parts?
You may customize the stop for fit but if there were a problem with cranks fitting or if the spacer were meant to be used to adjust for some mythical change in the crank bore like you initially stated, the stop would come in different sizes without the need for the customer to “customize” the stop.

But with your picture choice, we're also seeing that the removable spacers can be present even when not recognized for what they are.
Not “spacers”. Stops
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Old 01-27-22, 10:52 AM
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Originally Posted by Iride01 View Post
Sounds like a mess then. I just stick with octalink or hollowtech II. One and only one position the crank arms can sit on the spindle when properly installed.
Honestly, ISIS has the same “one and only one position” on the splines. The built in stops ensure that positioning. That’s why it has the stops which square taper lack.
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