Different Rotors??

[crazy steve]

I was working on my FJ fork swap today, and just couldn't get my measurements for centering the wheel and rotors in the forks and calipers to add up. I was using some spares as 'mock-up' parts (keeping my pretty polished parts for final assembly) and finally in frustration I checked all the various parts to figure out WTH was going on...

It seems I have two type of rotors, with a different 'dish' to them. Most of them are .760" from the wheel mounting face to the outside, but I have two that are .810". Even stranger, they're off two different bikes/wheels, all 78/79XS11s (but who knows if their original). Now, only .050" isn't a lot and the floating calipers on the standard would handle this with no problems. But on the Special with it's 'rotating' caliper, you could have a potential difference of .100" and that is a lot. The parts fiche only gives one number, but I find it hard to believe that Yammy missed the machining by that much (or that often; 2 out of 10).

I guess this is mostly just a heads-up for the guys with Specials; if you're having issues getting the rotors/calipers aligned, this may be why...

'78E original owner

[bikerphil]

With my FJ swap Steve, my wheel is off center about 1 mm and I have different thickness spacers on my left and right caliper brackets. I know your set-up is a bit different, but it seems to me that the spacing isn't super critical. Interesting about the rotors though. You are about to enter shimming hell, lol.

[crazy steve]

Yeah, you can't tell any difference by just looking at them; they appear identical. So that makes me wonder if there's another Yamaha that uses this specific rotor with the slightly different dish, or if they had two versions for the production line but 'cheaped out' on replacement parts. I've seen this before where the manufacturer has several different parts used on the line but a more 'generic' part for replacement to reduce inventory.

'78E original owner