I've got an old SOHC CB550 master cylinder, 14mm, and rather than using in on the KZ440LTD dirt tracker slash trail bike slash cafe racer side project here, I'd rather use it on my main project which is a DOHC CB750F, which is in the middle of a wire wheel swap (GL1000 hub with 3.00" Boranni rim 110/80zr18 front, KZ750B twin hub 4.25x18" Excell 160/60zr18 in the rear) and is as much as anything a DOHC sand-cast tribute generic UJM retro vibe type of build, and it would really benefit from a good old school master cylinder. Well, either one of them could use this style of MC. I'm whipping them both up for my step-daughter's 16th, if she's up to riding the big one, and I'm not yet ready to get back in the saddle due to health reasons well she'll get the big one, but in a perfect world we'll get to ride together, obviously. I guess I'm saying, IF this big idea of mine can be pulled off, or not, it's got a place in my parts pile.
One thing I was thinking of doing, was to cut off the alloy resovoir cup and braze it on top of a different MC, maybe the stock DOHC piece, it could even be filed down to bolt on top of the thing if needs be. Or, for that matter it could be cut off with a little threaded barb on the bottom to become a resovoir for a much more modern remote res type of system.
But what I'd most like to do, is hone out the existing piston barrel in the MC body, use a flat thin grind stone in a dremel so that a larger circlip will fit, and put in a different rebuild kit in the body. Maybe something like a 16mm or 18mm. Obviously, you might need to shim the spring, or use a longer stiffer spring, in the rebuild kit. But other than that, they're all the same stuff inside. Not sure at this point how big I can make the thing, but it looks like there are flex-hones available in all sorts of diameters. OR I could take it in to be machined professionally and hone it for final finish.
It would probably cost more to get the tools to do it myself, AND it would be a huge amount of time involved to sit there and spin the hone in and out of the port until the diameter changes as much as even one milimeter. Let alone several. Maybe it would even be good to go at it with successively larger diameter drill bits, THEN hone it, unless that would damage the surface too much. You'd need to drill only within a mm at the very closest, to the diameter you want. It's a heck of a problem for the home mechanic type, I think I'd like to bring it in to a pro brake shop or machine shop and see where it goes from there.
This would yield the most awesome classic MC for an upgraded brake system that you're gonna get anywhere. And all you'd need for a starting point is a cheap broken down MC body. For the lever, you might even wanna change some stuff up. I was looking at the lever off my DOHC MC, and it's got an even more stylized look to it, it's got a bigger ball on the end with more of a hook to it. Waaay nicer piece. And the ratio end of it is different. Hell this is the type of thing you might wanna carve up yourself, really. SOHC systems.
Unless that represents too much of a soft spot in the brake line? Maybe that sensor has too much play in it, and I'll wanna adapt some switches to the system? I've got a good selection of micro switches like this, not just the ones off the original bike, I've got a pile of them out of a computer printer I took apart a few years back, that are much like the bike light switches only even tinier and seemingly more sensitive, AND they're often covered in a rubber boot or even a coating of liquid latex sealing type of deal. If not, liquid tool handle etc. There's a lot of stuff like this, lots of switches of the type. The DOHC system has plastic switches that screw under the clutch pivot, the brake pivot etc, and none of them are even near as waterproof as the crap from the computer printer. Makes you think. But yeah, not hard to put the DOHC type switches onto ANY master-cylinder, just tap a couple holes and screw them in place, run some tiny leads, etc. So, I'd LIKE to use the hydraulic stuff, like I say. If nothing else, they're water-proof switches.
If the pivot point can be moved out further, through drilling a larger pivot hole at an offset center, round it out eccentrically, basically, and put in a larger pin, then there's a change to the leverage as well, just like you'd see on an adjustable system. Perhaps some kind of eccentric sleeve could be put in there, where you COULD adjust the thing. it's all just a question of what will still fit in the stock MC body's leverage bracketry, ie the two triangular projections that go to the front right side. It might even be something that could be welded up a bit. Best to weld it with similar metal, maybe rods made from another chopped up MC, so the metal will still match when polished. Me, I kinda think that mis-matched metal in a spot like that shows the work that was done, and isn't a completely bad thing. But it's food for thought, if somebody wanted to make one with a show finish. Brembo type pivot eccentric pin, maybe they have replacement parts, and maybe even take the ball off the DOHC lever and cut some threads on the stub of shaft left over, like they do when they put a larger more comfortable ball on the end of the lever of an old bolt-action military surplus rifle, when its "sporterized" or better still "accurized" for a sniper-variant clone. Either of which is the kind of language, the kind of aesthetic, which applies to what's being done with a bike. Ha ha. But yeah, take that same little ball end, maybe even take some ball ends made for the bolt action rifles, some of them thread right off of stock rifles and are replaced with the big stuff, and then you take whatever lever you're gonna use on the bike, whatever's got the right pivot end geometry, longer plunger contact arm so that it really squishes the piston into the MC body, whatever the lever is you wanna use ... a primitive shape cut from an alloy plate and then filed with a bevel all around, etc etc. My point being, the fancy ball end lever look can be put on another lever, simply by moving the ball over to the new lever. Ha ha. I think I might look at some of those bolt-action parts sites again. They've got some cool oval type ones too. Not that the same ergonomics apply here, you're not pushing the lever with that ball down in the cup of your palm, pushing hard on it with the heel of your thumb, etc. I dunno whether you'd want a steel on on the end either, 'cause that's not where you want your handle-bar end weight situated. But hey, maybe your lever itself has some harmonic vibration going into it. Ha ha. You could put the weight on it for that! Ha ha. You get my point. Of course, I know that you don't want a composite lever that'll be more likely to snap. But, one place you COULD put in an insert, would be to put an end on the part that contacts the piston surface. A hardened surface or even a roller type contact. 'Cause this is another way to change that pivot point thing too you know. The ratio has to change, but it could change at either end. If that piston contact surface only meets at the very very center of the piston, but you could contact with a push that moves from one side of the piston "crown" to the other side, of course without introducing any kind of stiction from the vector of the force - all the easier with a roller in that tip. Maybe something like a ball detent even. But me, I'm thinking better if it's just a good smooth hardened steel curved tip with some grease on it.... Anyway, THAT is another point where you can get some different geometry on that lever. Not as adjustable, but whatever. Me, I'm thinking of looking around at a lot of other Honda MC levers from across history, and seeing what's gonna fit. It also seems like other Japanese levers have the same pivot pin diameter, just a whole range of geometries available but maybe there's something that'll fit with a bit of cutting down, rather than building up.
I guess, what I'm saying is, there's a LOT of stuff to consider, for building the perfect MC. But I like the style, the aesthetics of the mould this is cast in, etc. It's a real classic look. And if I could have the diameter changed so that I could even go so far as using two of the same stock calipers, better still two of the stock calipers that came on my DOHC, best of all if it could be adapted in such a way as to use good six pot Tokicos etc etc, and then a person could look at whipping up a boutiue caliper that ANY Honda owner would want on his bike.
Some day, I'd like to try the things I'm doing with this '82 CB750F, on a modern Honda. A VFR1200 or something like that. I'd love the challenge of putting a wire wheeled hub on that single sided swingarm. Damn that would be cool. But of course, I'm thinking more along the lines of a CBR, of course. A CBR that's got elements of a CB750K, and a CR750, and A CB1100R, etc.
So I guess what I'm asking is, though I think the question of whether the DELUXE version of which I speak has only been imagined before, I wonder if anybody anywhere, has ever widened the bore of an existing MC. On anything. Bike, car, aeroplane, you name it.
-S.
