brake rotors

hi all, well i picked up a basket case last year and its been through some major changes
finally got it to the testing station today and i had missed a small crack in a front rotor
the rotors on it i think are C3 they are drilled, 4 bolt mount 78mm centres, 300mm o/s diameter rotors
but the bikes not a pure breed
and ive seen some f series rotors for silly money
are the F series rotors different to the c series?
looks about a 26mm offset but cant measure that properly till they are off
pics of the bike and rotor below
cheers in advance for the help

They may not be '79 kz650C3 rotors, as there are more holes than stock.
Can't tell if the C3 hole pattern is still there, but my guess if they are 4 bolt mounted rotors, they are from a '77 or '78.
No matter, as it's the number of bolts that mount that will narrow down your search.

I believe the offset of the front rotors between '78 & '79 rotors is the same, but the rear rotors do have a different offset, as a different rear master cylinder was used on the '79 C3.

I haven't got C3 front rotors to compare, but rear '79 C3 on left is offset more than the rear '78 C2 on right:

cheers mate, much appreciated
well after sifting through a parts bin found some which are the same fitting and offset with the sun star type drill pattern like the ones you showed above, from a Z750, barely any wear at all, and 70 quid for the pair a bit better than the 200 each EBC wanted
and as i turned around after the search spotted an old Z1R in the corner, same drill pattern as the ones i had with same 4 bolt fitting and sizing, so future reference means theres lots more choice than i thought
am still interested to know if the F series ones are the same, as EBC are selling off F series ones at 70-80 quid each and charging 200 each for the C series, and i know there was a caliper change but thought C3 had newer calipers?
so got a feeling they have just got an overstock they are trying to clear, because all specs ive seen say only disc changes were the slightly smaller ones used on the CSR etc, but there does seem a lot of contradictory info about, not helped by kawasaki and ebc quoting an "effective disc diameter" in one place and an "outside diameter" in other places, but sorted so thanks

I was thinking those were Z1R disks. I went from solid to stock drilled. They are 1/2 the weight and I think look better. Lots around too.
Steve

earthcore wrote: ....the rotors on it i think are C3 they are drilled, 4 bolt mount 78mm centres, 300mm o/s diameter rotors...

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As already mentioned those are Z1R rotors, 297 mm diameter to be exact.

The forks on your bike are from a B1 that came with a single 297 mm rotor and the caliper in front of the fork leg.
In the pic above you can see the fender stay mount in front of the leg, meaning the fork legs have been swapped and
turned around to mount the calipers behind the legs.

Rotors from dual disc models are only 276 mm or 279 mm and won't work with your forks - due to the larger rotor
the B1 forks have the caliper mounts placed higher on the lower legs than the dual disc models, using the smaller rotors
with the B1 forks will make the brake pads hang over the edge of the rotor.

And if you wonder how I know it's because I have the same setup, a B1 with swapped/turned forks and Z1R rotors:

cheers for all info mate
n nice lookin ride
thanks again
ian

I was gonna say, I've got some of these same weirdo style of randomly "gap-holes-gap-gap-holes-holes-gap" cross-drilled rotors, from a couple of KZ440's - and they definitely don't measure all the way up to 297mm's. I've got lots of Honda discs and a 4LS drum going onto the "KZ440LOL" - and the Honda discs @ 276mm and 296mm diameters, well I'm pretty sure the KZ rotors sitting stacked up with the rest are smaller than BOTH types of Honda rotors.

However I still feel there might be a good use for 'em. At least, this is how I'm looking at this stuff on the Honda version of which:

All the better that the KZ four-bolt rotor bolt-circle pattern & diameter etc are so close to identical in both front and rear types. I mean, it'll take SOME mill-work or at least drill-work, but it's not nearly as bad as the Honda predicament where the bolt-circle is substantially different.

Anyway yeah, these babies should be used for REAR brakes, IMHO. Sounds like Kawasaki did the same as Honda, in that when they built a dual-disc front end they went to smaller lighter rotors. At least Kawasaki had the good sense to include that 2nd caliper hanger on the opposite fork, in the later model series anyway. But way to get it backwards, hey? When you wind up with a great big rotor on the back wheel with a couple of smaller discs up front? Sheesh. The Honda GOLDWING had an early prototype version where they seemed to contemplate doing it right in the first place, but then there must've been some type of committee thinking here. That early GL1000 had the dual-296mm rotors up front, and a single 276mm disc in the rear. Well, I'm hoping to do 'em one better on my "CB900K0 Bol Bomber" by either spinning down the original disc to the desired size OR to fit up the CB350F/CB400F front rotor which was similarly built & styled, but only up to 260mm diameter. Sounds perfect for a late '80s early '90s rear caliper. In the Honda camp, the mid-late '80s first CBR (the HURRICANE, if it still haunts your KZ brand loyalist nightmares) went down to the 276mm rear brake, and it's caliper & hanger look nearly identical to the style employed on CB900F, CB1100R etc. So yeah, THAT should be an easy fix. All the easier if the OEM discs are simply spun down to size - usually leaving unmolested full-thickness material at the center area of the disc. Seems far simpler than carving up a new center carrier for the six-rivet composite CB350F/CB400F 260mm disc. The trick being to dig up a later era caliper & hanger which nevertheless seems '70s original. Was also wondering about taking one of the earliest calipers with the integral hanger and opposed pistons, and drill a new axle hole somewhere along the middle length of the hanger's arm. Would probably require spinning down a bit thinner then adding two more thinned down washer spacers on either side of it, but you can't beat the notion of an all OEM style, early version caliper - AND the matching disc, all set up for the modern compact lightweight rear hub ethos/pathos.

Paired up with one of these here KZ750B/KZ1000A conical rear disc hubs, and maybe the 3.50x18" Super-Akront rim - let alone the pair of 4.25x18" Akront rims I've got on hand for the Honda - heck I've got a BUNCH of sick fat rims on hand and those three only scratch the surface ha-ha. But yeah, the key being to max out the tire width at the hugest period-correct sizes, then at the same time lighten the rear hub down to the minimum feasible weight, lighten the rim etc - Now it's starting to sound like competition-spec running gear!

So I'm wondering if this is NEWS to any of you guys? Ha-ha. Anybody built a scaled-down but period-correct rear disc brake?

-S.

OH !!! - POST-SCRIPT:

If you're looking for "full-sized" rotors in as-new condition? Check out "METALGEAR AU" - in Australia - Somehow I'd thought it was AUSTRIA - gotta bone up on the abbreviations - These guys make a lot of cool discs! They make a replacement outer ring for all of these old composite rotors - and they'll do the rebuild job for you too, that's all included in their price. Powder-coating the carrier and everything! They test 'em for true concentricity & balance as well. Considering all of that, what a heck of a bargain. IMHO, the really cool thing to do is when you find an alternative style of center carrier which fits 'em nevertheless - true "Unobtainium" right there, if you've got the only pair like 'em on the planet! Ha-ha.
CHECK IT OUT - ALL OF THIS FOR $279.95!!!

metalgear.com.au/mgear-brake-disc-front-leftright-p-7417.html
AND HEY - they make replacement rotors for the '81 CB1100R aka CB1100RB - only 1050 units ever made. Though there are some mix-&-match applications on other Honda models where a buyer MIGHT wanna use 'em (ME for instance - the 276mm type DOHC Honda forks differ from the 296mm version only in the caliper HANGERS, ergo a much simpler swap than YA'LL gotta deal with!) - Now albeit, only compatible with the Comstar dual-disc or single-disc wire-spoke CB750K-DOHC front hub, OR - the one model only Canadian only POLICE only CB750P7 dual-disc wire-spoke FIVE-bolt front hub - Which is to say, still probably only less than 1500 potential bikes to put these discs on. And they're a DISHED type one-piece rotor, too.
metalgear.com.au/searchByBikeModel.php
metalgear.com.au/mgear-brake-disc-front-p-6786.html

So just take a minute to absorb how totally awesome it is that they ever BUILT these replica discs, now would you? Well, it's my hope that they'll be willing to offer these guys in a six-bolt drilling pattern, so I can use 'em on a more common front hub than that Canadian Police-bike front hub ha-ha, but also - I wonder whether they could ever offer discs such as these in larger diameters? Perhaps - instead of 296mm, how about 310mm like the Y2K+ CBR/VFR series, or even larger up around 320mm-330mm to suit the craziest modern forks out there? And yet keep the vintage style right down to the rotors? WOW that would be awesome. Might take a lot of pleading & begging, but it seems like a 296mm rotor is actually cut from a blank which might be closer to ... what? FOUR-hundred millimetres? Ha-ha. Really though, these dished one-piece discs are probably more like a batch-production thing, where they're all run off in a quick batch just the one time. But if not, if they're gonna come up with a 2nd batch? Would be nice to think there are some punched/stamped blanks laying around which haven't been spun down to size just yet....

Okay so for the more ambitious ideas such as this? Not a dead end - there's also the ISR company who make BESPOKE brake rotors. Which is to say, the type of discs which adorned Eddie Lawson's '81-'82 AMA Superbikes (I'm more familiar with their HONDA competitors' version of which, wherein there were 310mm floating [prototype CBR stuff?] rotors for the 16" front wheels, and 330mm FIXED rotors for the 18" version of the Morris & Dymag front rims, with the Lawson KZ1000R style huge solid monolithic un-drilled central carrier blocking all view of the hub etc.- Any of these could be YOURS - and probably for less $$$ than was mentioned above with respect to the EBC floaters. Would be nice to find somebody mass producing caliper HANGERS for such applications as well ha-ha. (ANYBODY? Seriously, identify the major models and their typical common upgrades etc, then start punching out hangers by the dozens, do a dozen or so versions - advertise 'em well enough, and your shop would be busy for the next few generations!!!)
www.isrbrakes.se/products/brakediscs/

By the way - it seems that the Honda 9-rivet carriers, or at least SOME of 'em anyhow, came with the same dimensions - 296mm outer diameter, 154mm center hole, 166 or 168mm rivet circle diameter. Well it shouldn't take THAT level of detail to tell you, when they're so damn similar you'd think there'd be a patent-infringement lawsuit ha-ha.

What I'm wondering is who MADE them? Was it ENKEI the wheel rim people? Was it STANLEY with the headlights & electrical components? Who were the major parts suppliers which cooperated across the board with the "Big Four" companies???

Does anybody know?

-Sigh.

OOOH - and with respect to what all I was saying before about the cut-down smaller diameter rear brake discs - The O.P. had that drilled disc which failed inspection 'cause of a small crack?

Well - how much is LEFT of the damn thing? Is the crack in the outer circumference?

After all, I'm looking for a smaller disc, one to fit these Honda carriers with the exact same dimensions! Would be a boon to "Re-Cycle" a doomed part such as this, hey? A boon and a kudos, I should think.

-Sigh.

hi mate, the crack is about half way between inner and outer holes
so dont think thered be enough to use for anything,
there is the 1 good one if thats any use but if ur in Oz shipping wouldnt be cheap as im UK
cheers