Originally Posted by
UniChris
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