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Yes, I'm wary of the mot situation but I've known my local tester for a long while and he's a sensible chap.
I may leave the old discs on 'til after mot time anyway.
I might even ask his opinion for future reference.
Oz .. thanks for looking anyway.
Tim .. I'll definitely pop over at some stage ... avec feelers.
On the bobbin material ...
I agree that it seems to make sense to have the bobbins wear in preference to the carriers.
But most of the aftermarket bobbins that I have seen in aluminium are hard-anodised 7075 alloy, same as Renthal sprockets, so those ones at least are not exactly soft.
To make my own out of such material would require subsequent treatment, ie hard anodising and maybe even some form of heat treatment, and all of that was just becoming too complicated.
On top of which, these discs came with stainless bobbins anyway, so titanium is no worse than that for being over-hard.
And .. I just happen to have some titanium in exactly the right size.
But the plot thickens, because .....
It turns out that the rotors on these discs are thinner than the carriers .. by about 0.018 ins.
I wasn't expecting that.
So I tried to imagine why.
I'm not sure that I have the answer but it soon dawned on me that the absolute minimum float that I can have on the rotors is 0.018".
This would require the buttons to be shimmed to zero clearance on the carriers, which is what I have done so far.
The rattle from the resulting 0.018" free float doesn't sound awfully loud when I shake the disc ... but it was loud enough for me to ask my original question about std bobbin clearance.
The best info that I have so far is that around 0.014" bobbin clearance is something like the norm (though this is not yet confirmed).
My gut feeling is that I would like to err on the low side of that if anything, ie maybe about 0.010" ideally, so 0.018 is getting a bit high ..... or is it ?
Because, with my bobbins shimmed close against the carrier, its only the rotor that moves, not the bobbins.
On the other hand, with "normal" discs where carrier and rotor are of equal thickness and the bobbins can move on the carrier, the lateral range of movement of the rotor is double the bobbin clearance. ....(think about it).
So maybe my 0.018" range of movement isn't far off my ideal of a tad less than normal.
Effectively its like having "normal" discs with 0.009" bobbin clearance.
Ok, if you're still up for this, there's one more thing.
Because the bobbins don't move (much) on the carriers, then maybe the wear is less than if the bobbins were loose in the normal fashion (I would say its highly likely).
And that is another reason why I might make my own in titanium.
Incidentally, these discs look like they've hardly been used and there is no discernible wear at the bobbin/carrier interface.
Indeed, the anodising on the mating surfaces looks pristine.
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