AHA! Damn, I've gotta admit, that's a really good pick for a substitute disc!
So am I to assume then from your pics of the rear disc adapter, that the four-bolt CBR rear disc, has the correct 120mm bolt-circle diameter, to hook up with two of those bolts directly to the hub? Was it a complete fluke finding one that fit? Or did you use some way of looking it up?
I've been reading through old Galfer wave-rotor catalogues, diagrams on every listing for cheap replacement discs, and best of all the Metalgear Australia "search by: bike-model/disc-diameter/bolt#/bolt-diameter/center-hole-diameter" function (which sadly doesn't cross-reference back to the model, so you can't necessarily use it to find USED discs & save a couple bucks aka cheat yourself out of a NEW brake) I've been searching high & low, but I haven't found a decent substitute disc that'll bolt up directly to this hub. (I DID find one for the 5-bolt Comstar rear hub - the ZRX1100/ZRX1200 discs fit though they might require a spacer of some sort....) I've gotta admit, it was stupid of me to dismiss the 4-bolt rotors (and 3-bolt and 9-bolt & 5-bolt etc) 'cause two out of 6 or 1 out of 3, that's still a pretty good connection, considering when it's a flat rotor you're stuck with using a spacer anyhow.
Either which way, this is a pretty clever mod. It almost looks almost perfectly period-correct. It's still got some CBR/VFR-ish, crotch-rockety vibes. Probably mostly coming from the gold anodized spider-flake/snow-web carriers in the floating front discs.
(((Never mind the Mono-Shock conversion, IMHO one sure-fire way to RUIN the good looks of ANY classic Superbike. You can see the direct comparison on the Kawa GPZ 550's & 750's from around the early-mid to mid-mid '80s, where the bikes look otherwise mostly identical, but the later versions go to the mono-shock.)))
vs
Or the early Yam TZ700's vs TZ750's, where THIS type of delicious vintage bike-porn
becomes THIS:
(((Ha-ha - Okay, so the TZ based DIRT-TRACK racers, many of which were already out there BEFORE Kenny Roberts got on board, were a TWIN-shock - but still, it's as extreme of a cool vs hokey photo comparison that I could dig up off the cuff)))
(((Heck even the vaunted CBX six ITSELF loses a whole lot of vintage cool character, when they stuck that Pro-Link rear end onto it.)))
vs
(((See what I mean???)))
(((But whatever. "To Each, Their Own" - I've put my own SPAM-filter on my bike-porn feed, so that I've only gotta filter through about fifty or a hundred pages of the "Bike-Burn", pipe-exif type "Starbuck's Racer" type bike-porn sites - to find a single, lovely retro TWIN-SHOCK Superbike.....)))
*cough*But YEAH - it's a SMART mod no matter how you slice it - I've been looking around for some decent alternate rear disc options, as I'd really like to shed some weight from the SOHC 'F1 rear disc hub
(((Did you know that the center section of this hub alone, weighs the same as the center section of the 4LS front hub from '72 Suzuki GT750J, a 200mm double sided drum hub? With the sprocket carrier, sprocket and rotor, we're talking double that - and the side-plates shoes cams and linkages from the 4LS are negligible, especially with the mods I'VE done to the 4LS on my teenage daughter's "KZ440LOL" project, everything ventilated & lightened, cross-drilled shoes etc, drilled hollow pivot cams - plus if you use the linkages from the T500 Titan 2LS drum, which bolt straight up, they're 50% lighter than the regular 4LS version! So yeah anyway back to the SOHC 'F1 rear disc hub, what are we talking about here? Something like 20lbs or 25lbs? There's gotta be a way to lighten the HUB, ITSELF, by drilling some holes in the cush-drive section, the sprocket carrier, perhaps spinning the whole thing down in a lathe....)))
It might be one whole functional half or third or quarter of what the rear hub does, but it's still the DISC, the DISC is the most superfluous thing on ALL of these bikes.
Next time, on my next DOHC-4 build I'm sticking a DRUM on the assend. Heck even up front, if you don't absolutely REQUIRE a disc brake I'd really rather have as big of a DRUM as will fit, and spend too much $$$ on that, if that's the "price" of avoiding a damn disc brake.
But IF you're gonna insist on a rear disc on a SOHC-4, and you insist on using the 296mm brake, I'd suggest using the DOHC dished one-piece version, which simply needs another 5 bolt holes drilled as everything else lines up just right. Even if you cross-drill the heck out of the OEM composite disc, it's gonna be heavier than the dished one-piece DOHC version - Heck, your CBR rear disc & that Aluminum adapter-spacer probably weighs more than the rotor of which I speak!
I'd use a drum on this one, but it looks like crap in the 4.25x18" Akront rim, it just makes everything look out of place, there's just too much contrast in the era of the drum hub vs the era of the huge fat Sports-Touring Radial tire in 160/60ZR18 which is more of a mid-'90s type of thing, ennit? I've got a 3.50x18" Super-Akront which looks LOVELY with a drum hub, far far better than it looks with a rear disc. But I want the bigger fatter tires on this thing, & I wanna seal 'em up TUBELESS - I've also scored an awesome 3.50x16" Super-Akront rim, drilled for the Harley rear hub aka Honda front hub pattern, which is gonna look sooo coool - but it's only appropriately matched to the wider version of the rear rim. I've also got a skinny 2.50x16" but it's actually HEAVIER, still requires an inner tube 'cause it's got no bead retention ridges, and tire selection shrinks ridiculously in that width - the 3.5x16" & 4.25x18" pairing gives a cool "Freddie Spencer Replica" vibe, yet it's off-set at the same time by the wire-spoke conversion, kinda dances across that line of Retro-Fried vs AMA Superbike Racer specs -
Now, I've scored another 4.25x18" (or rather, I got it before the "drum-drilled" version) which is drilled for a HARLEY rear hub, aka the "Front Hub Trick" - which would be awesome, but I need to find a better machinist before I dive into that one. I figure I'll use a GL1000 hub back there and the 6-section cush-drive cut off of this fire-damaged KZ750B/KZ1000A conical rear disc hub (the only damage is that the chromed-steel spoke flange on the small side popped off - and I've GOT another hub of the same type, but I don't have any rims drilled for the pattern and I don't trust that flange being held on with EPOXY - so I might just have 'em BOTH machined down 'cause I'm building at least TWO of these "Front Hub Trick" rear wheels, and it would be nice not to have to do a ... "not so quick, quick-change" hub thing, bolting & un-bolting everything on & off of the wheel each time. A huge reduction in machine-shop time for building one from scratch, not to mention it's cheaper than a lump of billet! HOPEFULLY it'll come out weighing less than the OEM SOHC CB750F1 rear hub? Add it up: the front hub plus 6 through-bolts holding the rotor on one side and on the other side the cush (cleaned up for absolute minimal weight, possibly cut down in width to help align the chain, skim the outer surfaces, cut off the spoke flange, put vent holes through the cush elements and sprocket-carrier etc etc) Maybe a later 'K8 style hub would help with the weight factor, and use shorter bolts but I'd really rather keep the full-length through-bolts so they'd be that much more resistant to shear - Might even "tune" the dampening rubbers by cutting 'em from some type of urethane/varethane, like Skateboard wheels type of stuff - they've got all of those different "durometer" #'s, and even if one can't find a cheap source of that material, there are always old skateboard wheels to use! Heck, I could almost see building a cush with actual skateboard wheels in it, or for that matter the grommets from the trucks, which come in a few different grades to - But yeah, with the thinner "pie slices" of cush dampeners, that's gonna convert the torque into more PSI spread over the lesser surface area of the cush dampener side-walls etc - So I suppose it should already have more "give" to it even with the stock, 40-yr-old rubbers in there. Meaning it'd be "tuned" already. Yanno what would be cool though, would be some crazy glow-in-the-dark urethane material in there, maybe with some LED's buried in 'em ha-ha - but yeah you could see the dampening action at night when that glow blinks on & off when you're accelerating/decelerating - It's just a brain-fart, but either way I do like the idea of removing as much as possible from the cush "dish" & the sprocket carrier - If the OEM rubbers have those little raised dots on 'em, probably casting sprue from their manufacture - I'd hazard a guess that you don't need to cover the entire face of the rubber - Just looking at the OEM Honda SOHC era dampener rubbers they've got the little spigot tab that holds 'em into the hub, and THAT doesn't brake off. So presumably you could drill a bunch of OTHER holes in there, and the rubber isn't gonna crumble apart & fall out of all the holes. There's also the section of each pie-slice where the carrier lugs sit, meaning nothing's working against the left/right or circumferential outer walls, so at THIS point you could definitely drill some big holes so long as it doesn't weaken the overall structure too much.... Of course, shedding weight is great up to a point, 'cause my main goal here is to look PERIOD-CORRECT. Otherwise, might as well "throw some Super-Moto wheels on there and call it done", as somebody once suggested to me. There are numerous period-correct wheels which had their OWN bolt-up cush-drive. Practically all of the aftermarket Cast/Mag wheels, whether Aluminum OR Magnesium, in every case at least their early versions of which, all had a bolt-up cush-drive. On the KZ1000A which Jim Goose / Steve Bisley rode in "MAD MAX", on plenty of Ducati bevel-twins, AND most importantly on the '76 RCB endurance racers with the prototype COMSTAR wheels, the rear wheel is a compact lil' core with a bolt-up "dish" for a cush-drive. Like a bundt cake pan. So there's nothing really that SKETCHY about it - There's certainly something sketchy about the way MOST folks have done the "Front Hub Trick", 'cause they so often leave out the cush-drive altogether! But yeah, the real CHALLENGE here is gonna be to get the weight down somewhere between the SOHC CB750F1 OEM rear disc hub, and that Kawasaki conical hub - which is probably impossible to beat, weight-wise at least.
The thing is, I've already GOT the SOHC rear disc hub just sitting here. I've got the rim, I've got the rotor, and the spacers from the DOHC all line it up perfectly. That, and there are the dished rear rotors from Cycle-Exchange, which I'll have to mill down the sprocket carrier for, to match the off-set of the CBX pro-link front sprocket. I suppose that means there's SOME machine-shop time. But yeah, I figure it's still worth using the SOHC rear disc hub if only for a while. Down the road, I plan to use the rim on a SHAFT-DRIVE bike, with a WELD-UP type hub conversion where the donor is welded into a hollowed-out DRUM - This rim itself is my whole inspiration for wanting to build a Gold-Wing next. That is, IF this size of rim & tire can squeeze into the 'Wing's swing-arm? GL1100 swinger on a GL1200? I'd really hate to have to modify THOSE parts! Surely, it's still probably cheaper to go after a crash-damaged GL1200 than a decent GL1000 - those extra cc's are well worth the trouble of a weld-up hub! But a modified swinger and drive-shaft? Yikes!
All I'm saying is, it's not like I'm complaining about the "drum-drilled" version of this rim! It's STILL worth completing the wheel build, even if it means swapping out the hub down the road. Even if it means I'm building a wheel that's even HEAVIER than the Comstar that I'm replacing.....
(((All the same like I say, on THIS bike, I'd really rather have a DRUM back there! It would simplify my rear-sets by a whole order of magnitude.)))
I've got all of this SOHC rear disc hub stuff for my wire-spoke DOHC conversion, the "CB900K0 Bol Bomber", so what I've got right now is the twin-pot rear caliper which is decidedly unstylish compared to the early type '75 'F1 opposed-piston non-floating rear caliper with the integrated carrier - I'd LOVE to use one of those, but I've got this Cal-Fab swing-arm & Marzocchi Strada-II shocks which have no outward canted off-set to the piggyback reservoirs - so the swing-arm wants the piggyback switched around to the rear so they don't "kiss" the swinger when the shock extends when "catching air" at the top of a hill, yet the CALIPER does a lot more than merely "kiss" the piggyback -
Hence I need to make some serious changes to the rear brake fitment or clearances ANYWAY.
And there's an identically styled twin-pot floating caliper from the FT500 Ascot, (((which uses the same 5-bolt pattern as the FRONT Comstar wheels on it's REAR wheel, so identical front & rear just like an old Yamaha RD etc - it uses a 276mm rear and 296mm dished one-piece rotor up front!)))
And it appeals to me that it would look "period-correct" to the DOHC era at least, and shed some substantial weight. IMHO this is a great mod for all of the DOHC-4 series CB900F, CB1100F, CB1100R etc - even CB1100F USA spec cast/mag wheels could swap the smaller 276mm front discs onto their rear wheel - It's far better to have the 296mm discs up front if you can swing it - tougher to do on the 39mm TRAC forks, but you should swap to the 41mm TRAC forks anyhow, either GL1200 with the same puny lil' 15mm axle or GL1500 for 20mm axle upgrade -
(((Talkin' 'bout the 20mm axle upgrade we should ALL be doing with our OEM forks on both SOHC and DOHC models, Gold Wing, etc etc - IMHO this would be a HUGE improvement, and I don't understand why there isn't a conversion kit!!!)))
SO - I've been LOOKING at either cutting the thing down to 276mm, OR swapping the nine rivets out for bolts and putting a 276mm version on it, from a front disc - preferably one of the later types from GL1200 etc, with the spiral grooves carved into the surface. That would look pretty cool.
And as for the FRONT brakes? I'd love to pair that DOHC style rear slotted/lightened 296mm OEM disc, (only cut down to 276mm of course) with the 296mm VENTED discs from CB1100R, CBX pro-link, GL1100A & GL1200 - That's what I've got on the bike NOW, as they're such a killer upgrade from the 276mm OEM CB900F discs. HEAVY as #$%* though!
And it's cause of THEM, that I sure wish I could keep the 5-bolt carrier up front. 'Cause you could have the regular CB750K0 look, the 9-bolt 296mm SOHC discs in the form of the CB750A Hondamatic front disc -
PLUS you'd also have the option of using all of the cool 5-bolt types from the DOHC era & later Gold Wing etc.
But the dual-disc 5-bolt wire-spoke front hub, from CB750P7 Canadian-Spec & possibly also Filipino spec POLICE bikes - ONLY - is one very rare piece of Unobtainium. Sure, you could use the bolt-up Comstar conversion front hub, but that's heavy as all get out! The disassembled Comstar front hub is ALREADY just as heavy as the SOHC/'Wing 6-bolt dual-disc front hub. I'd imagine the DOHC single-disc 5-bolt hub COULD be some weight savings, but modding it to take dual disc? You might as well get two of 'em and have 'em welded together. Or better yet? Use a HARLEY front hub, as there are plenty of aftermarket hubs for Harley with the dual-disc 5-bolt etc - but spacing those discs & adapting the metric bearings etc, it's gonna be expensive enough you might as well have an entirely new HUB made from billet! WTF.
So the CB750P7 SOHC POLICE front hub might be expensive, but IMHO it's well WORTH IT. However you slice it, whether it's drilling out 9 rivets per disc, replacing 'em with really good shoulder bolts (possibly the rebuild service from Metalgear AU, where they blast & re-powder your center carrier, replace your outer disc with any of several options be it cross-drilled & skimmed or extra thick even, then assemble the discs & test 'em for balance - maybe THEY could be persuaded to sell their bolt set separately? Adding it up, to skim & drill & re-paint some crappy old discs,
But oh, how I'd love to pair THAT hub, the SOHC CB750P7 wire-spoke 5-bolt dual-disc, with the 296mm dished one-piece 5-spoke (SOHC 'F2-style or rather DOHC '79-'80 style) 296mm FRONT discs - which came with the '81 only CB1100RB -
Now keep in mind, this following pic is of a 19" front wheel, (on Haslam's racer at Spa in late 1980) so just picture it on an 18" rim instead, that's when it would acquire it's Nth degree of awesomeness - as if it's not already there:
(Incidentally, these once Nth-level Unobtainium discs are now also available from Metalgear Australia) This would be the way to build the perfect FEATHERWEIGHT front wheel, preferably with an early Akront or "Super-Akront" in 2.50x18" or 3.00x18" - which are rare as hen's teeth, ten or twenty or a hundred times more rare than the 3.50x18" Super-Akront - I've seen a pic of 3.00x16" for sale, and a picture which LOOKED like the 2.50x16" version - If they're anywhere near as light as the 3.5" version? I've got 2.50x16" TC profile Akront and it's waaaay heavier than the "Super-Akront 3.50x16" you see - they're not suitable for tube-less tires 'cause there's no bead retention groove ... heck neither does the 2.5" TC rim that I've got ... but wtf even with a lightweight inner tube, these early "Super-Akront" rims would still save weight over any other type of rim you could find!
Like I say, I'd really LOVE to use those 296mm dished one-piece discs up front, with a 296mm rear dished rotor cut down to 276mm, or better still a "Front Hub Trick" Comstar rear wheel using the 240mm disc from CX500 & GL500 etc, which is both period-correct and Honda OEM AND it probably weighs less than any of these later CBR/VFR rear discs in the same size range. I kinda like the thought of the 296mm rear dished rotor cut down as small as you can go, and with the right caliper & pads it might even be possible to get it down around 260mm it's tough to say.
But yeah my point being, the embiggened CB1100RB-replica discs (or FT500 if you're on a budget) heck maybe even 296mm REAR dished rotors on some type of lightweight adapter? Either which way - dished Comstar 'F2-style rotors big ones up front & a tiny one in the back right in keeping with proportions on a CBR900RR or early CBR929RR etc. With the widened/lightened rebuilt Akront "NERVI" 18"/18" rims?
Now that would kick ASS on a Comstar equipped SOHC and/or DOHC bike!
Though to tell the truth the heat-sink factor isn't great with those dished one-piece rotors. The WEIGHT factor is incredible. I've compared 276mm GL1000 9-rivet composite discs vs the 276mm CB900F dished one-piece discs, and the weight is HALF that of the composites. And considering the carrier is the same size, the weight factor should be an even steeper ratio when the steel portion of the 296mm CB750K0-'K8 / CR750 style composite rotors - So the CB1100RB & FT500 Ascot dished rotors are probably more like 40%-45% the weight of the composite versions.
And these VENTED discs are even heavier still. The CB1100R-C/D '82-'83 style, the double-sandwich layered or "automotive style" rotors with the spiral slotted hollow grooves in the middle - a directional vane to throw air around. (Seems to make sense that the air moves from the middle outward, to "throw" the air rather than "catch" it. Right?)
And there's a REAR version of this sandwich layered extra-thick HEAVY-assed disc. Comes with the rear wheel on GL1100A Aspencade, and nothing else of which I am aware - Perhaps some version of GL1200 used it? Well that thing can't be cut down to 276mm, not without removing too much of the working surface, which is only as wide as the pads themselves. If it were an LP record on wax, we're talking maybe a 3-minute song. So not an option to cut it down - Though one might find a match in some of the later era YAMAHA vented rotors, which are smaller than 296mm IIRC, maybe 285mm - there are some odd-ball rotors you could use, though IMHO it's way too heavy so if you'd WANT the thing you might as well use the 296mm version anyway. There's a 210mm version on VF1000R, with an under-slung caliper no less. Which would be cool on a "Front Hub Trick" rear wheel, with a bolt-up cush-drive & a Harley pattern drilled rear rim. That's a pretty cool way to do it, IMHO - to keep those heavy crazy ROTORS, and compensate for it by shaving the weight from the rear HUB. Or possibly the KZ1000A/KZ750B conical rear disc hub, with a rotor carrier adapter. But IMHO, you don't really NEED that vented rear disc for it to look "Period-Correct" anyhow, 'cause anybody familiar with the CB1100R or CBX etc, would expect to see the composite riveted rear disc anyhow.
However it does point out the three/four main different versions Honda rotors in that SOHC/DOHC period, each paired in 296mm front vs 276mm rear (or smaller).
I suppose there's still another option is if you're using the early SOHC composite rotors, would be to pair the 260mm CB350F/CB400F front disc on the rear. I'm not of the opinion that it's a good FRONT brake, but it's got a certain quirky sex appeal all of it's own:
Ha-ha - Is it SEXIST at all, to say that I like what I'm looking at, but it only belongs on the BACK end of a motorcycle??? Ha-ha. Yeah, don't worry about it - my own lil' GRRRL will slap me for saying #$%* like that, so you don't have to!
No really though, IMHO that's the most perfect disc for a retro-fried Honda rear wheel, PERIOD. Paired with dual 296mm CR750 style front brakes, and the right choice of a rear hub ideally one that doesn't weigh as much as a boat anchor....
It's sexy stuff!
Sadly the center carrier can't be machined down to suit the rear 'F1 disc hub (OR the Comstar for that matter) - the bolt holes would fall right in the middle of the "dished" section, such that even if you spun it down flat on the back-side & counter-sunk the bolts to make it sit flat, there'd be practically zero material thickness left in there, it'd be too flimsy to trust it. So it would require a custom made center-carrier. However I'm sure the center carrier could be modded to suit a "Front Hub Trick" rear wheel, obviously a 36-spoke version (though I want at LEAST 40 heavy-duty spokes on my Superbike wheels! I'd like the KZ1000CSR 48-spoke rear hub if it weren't so damn heavy!) The SIX-bolt front hub would require the center-hole and probably all of the 6 new bolt holes. And probably a small spacer in any case.
But it would look BEAUTIFUL - like an actual factory racer might have used, IF Honda had a more progressive attitude toward rear disc brakes! 276mm is probably more realistic to expect from them, and indeed there are pics out there of the prototype or pre-production GL1000 Gold Wing, using the 296mm dual discs with the 276mm on the rear. So obviously they'd at least TRIED it. Remarkable then, that the '76 RCB Endurance racers used the 296mm rear - I think there must have been some issues with brake fade, where 24hr Endurance racers probably had to use the rear brake when the front discs faded & became useless.
Either way you slice it - that 6-rivet 260mm front disc is a beautiful period-correct match, as a rear brake paired with the 9-rivet front. If you could make a carrier which LOOKS period-correct, with 6 large lightening holes drilled around the circumference. Cross-drill 'em front and rear, and IMHO this would really kick ass - If only there were a rear caliper to match the 260mm diameter, with that same style of integral carrier as the '75 version.
I could see myself using the 260mm 6-rivet discs on maybe ... maybe a replica of the MT125R Elsinore-based ROAD racer (never heard of it?) I'd really rather build a replica from the 250cc Elsinore, or more to the point any of the biggest air-cooled 2-smoke single-cylinder engines which Honda ever BUILT - and didn't they do a limited edition XR600 or XL600 with an air-cooled head? For which you could probably get a 750cc big-bore kit? Yeah, NOW we're talkin'..... Ha-ha. Okay - so maybe more like ... a CB125 or thereabouts. But for THAT, I'd really rather have a DRUM brake up front! I could maybe see using some dual 276mm discs on say, the CB250N or CB400N/CB400T Hawk, but only in the case of building it as a CB1100R/CB1100F replica where you're looking for that same STYLE - I'd use the 276mm to replace the dual 240mm on the front of a CX500 or more like CX400 Japanese-market grey import! But a CX650E I'd probably wanna throw the dual 296mm on that. There's a very narrow window of applications where I'd wanna build a bike with those smaller rotors on it. So too, the CB550 276mm composite discs, I could see that on a CB350F or CB400F, probably not on the CB550 itself, but yeah that one's on the border area - On the GL1000 though??? Ridiculous! DEFINITELY needs the whole front end upgraded. At least, the way I'M gonna ride the lil' 'Wing! (Talkin' like, rip the truck-balls off the underside type of #$%*....) A very narrow window where I'd wanna use the composite 276mm discs, let alone dished one-piece 276mm, let alone the 260mm & 240mm versions.
It would boil down to - IS there no lighter-weight DRUM brake which will work just as well (if not better), OR - is there some aesthetic consideration which requires the discs to emulate some famous racer or other. The rear "Front Hub Trick" wheel with 240mm disc for instance, probably wouldn't compare favourably (WEIGHT-wise that is) with the 140mm/160mm rear drum from CB350K etc wire-spoke, CB400T 5-spoke comstar, or XBR500 Boomerang Comstar / MVX250F slotted-Boomerang etc ... Was there a drum in the NS250R rear 6-point Comstar?
I guess it depends on your riding STYLE, but to ME the rear brake is for a PANIC stop when the front brake fails, and the fade isn't a consideration 'cause in that #$%*uation you don't NEED to repeat the use of it, 'cause you'll be stopped at road-side cleaning out your shorts just long enough for it to cool off! Then you'll get home slowly and FIX the front brakes before you go out again! So yeah, so long as it's just adequate for that purpose, it's all about shaving the WEIGHT, or for aesthetic considerations! And a drum is good for ALL of that good stuff.
The cool thing about some of those smaller rear drums, is there are 2LS shoe-plates to match 'em, from plenty of early '80s dirt-bike drums, some of which are Magnesium no less. How could it be more retro-awesome to fit a rear disc to these smaller bikes, or even the bigger ones for that matter? I'm really keen to try a cross-drilled drum hub - on a bolt-up drum like the Harley "Juice-Drum", it should be no different than an automotive drum of the non- "AL-FIN" type, and the vintage Hot-Rod & Muscle-Car guys say cross-drilling the rear drums is equivalent to a rear disc conversion!
(((I dunno how you'd calculate it, but I'm sure there's a way to cook up a disc vs drum test on 60-to-zero stopping distances with otherwise identical bikes, 'round THESE parts anyhow!)))
Like I say, I feel the 296mm dual-disc FRONT is a must for the DOHC heck even a 750cc build, and so for THIS one I've already swapped over to the 296mm VENTED rotors as per '82-'83 CB1100R, CBX pro-link, GL1100A Aspencade etc - And to match THEM, I've got the CBX pro-link caliper hangers up front, with the 39mm CB900F fork.
Also interesting to note that they got AWAY with those dished one-piece discs on the first-year CB1100R - the fact that they jumped up to the vented type, (((taken FROM the '81 Gold Wing Aspencade, as the CB1100R-C/D and CB1100RB too, were a bit of a "Parts Bin Special" after all))) And if you look at the non factory-team Endurance Racers, like DHOLDA, especially NOW with their rebuilt racers on the Bol D'Or Classics series they've settled on those vented GL1100 & GL1200 discs, not even cross-drilled. And they've spent some big $$$'s on lightweight RIMS to run 'em on. There's gotta be SOMETHING to 'em! But of course I'm not suggesting this feather-weight dished one-piece rotor stuff for a really huge 999cc Japauto VX1000 or a CB1100R, I'm talking about a 736cc SOHC 'F2 or DOHC CB750KZ, CB750C & CB750FZ etc. And maybe the single layer composites on the CB900F, or my 985cc "Bol Bomber" - and the bigger stuff yeah definitely swap the vented double-thick front discs onto 6-bolt carriers if need be - And WTF, if you're planning a trip over the "Great Divide" in the Canadian Rockies, where possible bumper-to-bumper traffic can mean the whole ride down to sea level amounts to turning the bike off or at least kicking it into neutral, or worse yet running at speed with short vehicle intervals and using the engine braking the whole way in ADDITION to riding the brakes the whole damn way??? YEAH - for THAT type of crap, I could definitely see myself wanting that 296mm vented double-thick rear disc off the GL1100A Aspencade! No question. Might just wanna hang onto the 296mm-spec caliper-hanger for that expressed purpose....
And for the fastest like 140HP 1123cc CB1100F/CB1100R or RS1000 etc, I'm thinking some embiggened 310mm-316mm-320mm rotors (preferably fixed non-floating, stuck on later version ie spiral or flat-solid GL1200 or VF750F Boomerang rim type 9-rivet carriers, with the larger diameter rivet circle - MAYBE an OEM composite-riveted style rear disc. Still, PREFERABLY on a lighter weight rear HUB if you can swing it!
It's a pity there aren't any extended caliper hangers to use the EARLY, single-puck calipers, with the 296mm front discs. IMHO that's a way better "Retro-Fried" look, and would be hella cool suitable for an early RCB or RS1000 replica, where Comstar rims were paired with composite type 296mm discs which had that solid plate style center carrier - the later GL1200 carriers would be a good substitute for these, possibly drilled with the larger holes etc. Or often the SPIRAL pattern carriers, as per CB1100F & VF750F Boomerang rims etc - And like I say, some of those later carriers apparently have a larger diameter of the 9-rivet carrier, which is to say the outer rotor makes up less of the overall disc, less WEIGHT etc. IMHO there could be a really cool upgrade made with these, if they could be upgraded with an even BIGGER front disc, perhaps 310mm, 316mm (to suit the '96+ ST1100-ABS 43mm one-side-TRAC anti-dive type fork!) or 320mm to suit even later forks - If it's the solid plate style carriers, then it could be feasible to drill the big holes around the exterior of the carrier, to mimic the SOHC 'K type discs but proportionally larger you see, 'cause the discs wouldn't look out of proportion with that larger 9-rivet carrier. This could be a really cool "stealth" upgrade, IMHO - If only there were some caliper hangers to suit! Something to hang either a swinging caliper hanger from a conventional CBR/VFR type 43mm+ fork, or perhaps even just a straight bolt-up FLOATING caliper as per the SOHC 'F2 & early DOHC calipers, the single-puck type - but on a 43mm fork to suit 310mm discs - but I'D even be ecstatic to see the 296mm on 39mm fork, with single-puck calipers or opposed-piston single-pair calipers. For the AESTHETIC, to sneak it in all "STEALTH" mode, onto a SOHC/DOHC bike whether it's an early 'K style or an 'F1 wire-spoke, or the 'F2 and/or DOHC with the widened & lightened 18" front Comstar - To upgrade the SPECIFICATION to the later era performance but to keep the AESTHETIC of the earlier bikes. I think a kit for that type of conversion could be very popular with folks who RACE, on both the SOHC Sand-Cast or CR750 style builds OR the DOHC stuff be it the RCB/RS1000 replica stuff and maybe even the "Freddie Spencer Replica" Superbike stuff. Of course, us DOHC people can make really good use of the later TRAC forks, be it 41mm from GL1200 & GL1500, or possibly even a 43mm DUAL-TRAC fork made from two right-hand-side legs from that '96+ ST1100-ABS fork, which is set up for 316mm discs - Which is to say, this single-puck fork which I propose, probably has more footing with the SOHC-based application....
Incidentally, for the upgrades which DO exist already? These CBX caliper-hangers also fit the 35mm 'F2 SOHC forks, 35mm early DOHC forks, 37mm forks on '82 CB750F & GL1000 Gold Wing, & 39mm from Pro-Link CBX & CB900F & certain GL1100 models etc - They all look more or less identical, so IMHO if you're running a SOHC 'F2 with the OEM look you should be running the 39mm fork from the 900, with a fork brace you wouldn't notice the grooves at the top which give away the DOHC origins - and with that 20mm axle mod that would be an AWESOME front end for the SOHC 'F2, especially with CB1100RB dished one-piece 296mm discs up front, on an 18" front silver Comstar ideally re-built with a 2.50x18" Akront "NERVI" rim which is approx 40%-45%-50% lighter than the OEM Comstar type in equivalent sizes- (If you're interested, there's also a 1.85x19" version to be found on an Italian road-bike wheel, but I'm thinking about buying one on eBay right now so I don't wanna blab about it until after - I'd really rather find a 2.15x18" or better yet 3.00x18" or 3.50x18" but whatever, IMHO the 1.85x19" is still SOMETHING of an improvement over the stock Comstar wheel, even though I'd really rather run 18"/18" - the 3.00x16" from the same Italian bike with the 2.50x18", together would make an awesome pair for a CB750C, or better yet a cool FRONT wheel on say, NS400R or VF1000R etc.....)))
But yeah the regular OEM '82 CB900F 39mm fork which is currently on the bike, is soon to be replaced with a GL1500 fork (which I've JUST bought), & then used as a "hand-me-down" for a light-weight DOHC 750 I'm collecting parts for, for my daughter as a highway bike, with some killer 2.50x18" Borrani & 3.50x18" Super-Akront" rims, but heck I'm also considering a 16" wheel-set on that bike, possibly this 2.50x16" Akront TC rim up front with the 3.50x16" Super-Akront on the rear, for some later '80s style Superbike tires, or better yet another 3.50x16" Super-Akront up front with a 4.25x16" or 5.00x16" on the rear, though I've also got some hokey Super-Moto style 40-spoke Harley-pattern-drilled rims, in 4.25x17" & 5.00x17" - I'd really rather run a DRUM on the rear - heck I'd really rather run a drum up FRONT on that bike, but IMHO the Fontana 250mm or Yamaha 260mm 4LS drums would barely cut it on a DOHC or even SOHC 736cc build - ANYWAY yeah, there are all sorts of awesome light-weight alloy wire-spoke rims for that next 750 build, and yet at the same TIME I'm cooking up plans for some awesome COMSTAR wheels.....
TOO many ideas! Too many styles which appeal to me, each in their own right just as awesome as the others. I'll probably wind up keeping the 41mm GL1500 fork on THIS bike - but I'm still keen to carry off that ST1100 43mm "can't dance" (two left feet?) version of the front fork. And being that I've got this other DOHC project already gathering steam, the next bike I'LL upgrade to probably won't be another DOHC - not unless a CB1100F or CB1100R comes up for sale in my area for cheap! I've had this vision in mind, this day-dream, about an homage to the CZ Type 860, rendered from a V65 Magna or V65 Sabre - OR possibly even the V45 750cc versions, IF the Russ Collins RC-Engineering STROKER-CRANK kit is in the area of 860cc's? The V65 version is something like 1230cc's - WOW. Now that one would be well worth building, just 'cause it would blow away anything else in "Forgotten Era" racing. Preferably with an outrigger-bearing type shaft-to-chain-to-BELT conversion kit, ala Magni MV Agusta, or Yam XS-eleven for that matter. That would really open up the rear end for a bigger rear wheel. Preferably the Magna, 'cause of it's twin-shock rear end. Though the Sabre has that wonderful gas tank & all - IT would make for a better conversion to an RS850R replica, basically the same thing but with Cast/Mag wheels on it, or later era 6-point Comstar wheels ala NS400R/VF1000R etc - Obviously BOTH of these two V-four conversions have gotta be built by SOMEBODY. I'd be content with either, then I could literally die happy - no doubt wrapped around a telephone pole ha-ha. But yeah, even an 860cc Magna is just that much more powerful than any DOHC-4 I could ever cook up, so IT'S gotta have the 43mm TRAC fork on it. That, or a GL1200 based homage to the DLF-1000 Gold-Wing endurance racer, these would BOTH appreciate an upgrade to the whole front end - both would appreciate a wire-spoke wheel conversion. If I can find an MVX250R & build a replica Jawa Type 673 from THAT, it would probably be the most awesome of the three possible builds, but there's no reason to throw the 43mm TRAC fork or 316mm rotors at it, not the GL1500 wire-spoke converted front hub with 316mm discs as a "Faux-Leading-Shoe" brake but rather a 296mm conversion of the 276mm PC800 Pacific Coast front hub, ideally laced to a 2.50x16" front rim with 3.00x18" or 3.50x18" rear - An awesome upgrade for that little bike, but not enough to expunge my fantasies about this ST1100-ABS 43mm fork, replica of the NS500/NSR500 43mm TRAC forks - As such, it wouldn't be enough to finish me off for good.
Just one more - two more - three more - no wait FOUR more motorcycle build projects, and I can let go of this #$%*! Meh - Possibly two. At this rate, I won't LIVE long enough to complete all four of those ideas.
-Sigh.
