[66Sprint]

Preface:
Thanks to Jim, a generous member, and with a little added scrounging, I have most of the parts necessary to convert the front brakes from SLS drum to hydraulic disc on the 1963 Honda C 200 (90cc's) I am building for my 14 year old daughter .... While this particular example actually does NOT belong in a "twins" forum, the basic proceedures apply to a similar conversion on almost any bike, so I am including it here......Hopefully our new administrator will allow it to stay...... Steve

Project goal: To convert a small, single-leading-shoe drum brake to a disc brake set-up....
Here is a pic of the original set-up....

Immediate problems:
(1) This particular example has the Honda "bottom-link" suspension, and the fork width is very narrow (90mm) at its thinnest area.... Fortunately, the "links" project forward a bit and have a bit greater width at the axle clamps, so the "bare" spool hub has plenty of room on each side with the wheel centered on the stem.....
(2) The stock Honda rotor has an offset of 20mm..... With the wheel centered, I have only 13mm of clearance, so a "flatter" (less offset) and/or smaller (won't project into the constricted area as far) disc must be found and fitted...
(3) A smaller, less offset disc places the caliper closer to the hub where the spokes are at their widest, so a very small, thin caliper must be found and used..... This also means I'll have to fabricate a bike-specific carrier for the caliper....
(4) The generously donated wheel is actually from a CB200, and utilizes a 15mm axle while the original wheel used a 12mm axle, so this will entail several modifications to the "lower-links"....spacers, speedo drive, etc, not to mention I'll have to shorten a 15mm axle to fit the narrower width forks......

COOL!.... Now that I know what I have to do, I can proceed!.....

Step 1..... Assemble a pile of parts possibilities.... ALMOST done... I still lack a speedo drive gearbox/spacer, but can proceed with the rest.... "We dont need no stinkin badges!"...er....speedo drive (for now).....

Step 2... Find a rotor and fit it to the wheel.....
I intend to use a roughly 7" diameter rotor with a 10mm offset instead of the 10.25", 20mm offset CB200 stocker..... I found this rotor on one of those Chinese manufacture "scooter-mopeds" so popular now..... After machining out the center to fit the hub and drilling the mount-stud holes, here is a pictorial comparison....
The "new" rotor will be lightly surface honed before actual usage....

And here are some pics showing the (lack of) clearance I have to deal with....

I'll cover steps to correct problems 3 and 4 in my next post on this topic..... Steve

 

[bill440cars]

Hey Steve. A person just doesn't realize how what kind of things are going to have to be dealt with on a project until the situation is right in front of them. You have place this one in front of us and I'm really impressed with this undertaking (as I usually am, with your projects. The part that I'm really wondering about is where and how you are going to mount the caliper. I'm not saying you can't DO it, I'm not sure just yet how AND where. I figure you'll work it out, if you haven't already. Lots Of Luck with it Steve.


Later on, Bill

 

[66Sprint]

Bill, not to reveal too much, but the caliper will be mounted on an essentially "Y" shaped yoke that "floats" around the wheel spacer for that side (axle runs through at the bottom of the "Y").....It will be secured to the torque stay point on the fork leg by a Heim-jointed link, allowing the wheel and entire assembly to move (rotate and "bounce") as the rocker links do their thing...... There's more involved, but that's the basics... Steve

 

[inline4]

Hey Steve. A person just doesn't realize how what kind of things are going to have to be dealt with on a project until the situation is right in front of them. You have place this one in front of us and I'm really impressed with this undertaking (as I usually am, with your projects. The part that I'm really wondering about is where and how you are going to mount the caliper. I'm not saying you can't DO it, I'm not sure just yet how AND where. I figure you'll work it out, if you haven't already. Lots Of Luck with it Steve.




Later on, Bill

:mrgreen: :mrgreen: :mrgreen: :mrgreen:

 

[66Sprint]

Today's Update......( Isn't that redundant?)... Oh well, here goes.....

Since some of the parts I'm using are either NLA or extremely hard to find, I've decided to refrain from modifying the original rockers... (That way, It could be returned to "stock" if desired later).... This necessitates using a 12mm axle in a wheel designed to use a 15mm axle.....
Here's the plan:
First, I removed the internal bearing spacer tube from a "dead" wheel (old KX60 rear wheel, beyond repair)... This gave me a steel tube that already internally fits the 12mm axle. It is long enough to "cut to fit" AFTER the outside diameter is turned down to 15mm (to fit INSIDE the existing bearings and spacer tube within the CB200 wheel). This gives me a solid support/spacer for the smaller axle within the wheel.
The speedo drive I'll use will be from a 12mm axle smaller bike (yet to be located) and the disc side spacer will fabricated with a 12mm center hole and 23mm outside diameter (fitted to the bearing center and existing seal)... An "over" tube on that spacer (slightly shorter) will act as the pivot and support at the base of the "Y" that holds the caliper...... Interestingly enough, these sizes allow me to use a CB 750 swingarm bushing and a short, cut-off part of the swingarm as my "Y" base-tube allowing smoth motion for the caliper carrier
well, that's the plan anyway..... I'll post pics as soon as the fabricating is complete
.... Steve

Edited due to the fact that I haven't decided whether to use the 185 or 750 option yet...both have certain advantages, but a steel tube on a bronze spacer bushing is what I really want..... S.

 

[bill440cars]

Yep, just as I figured, you had it pretty much figured out! I should have known that, without asking at all. The narrow space that you are dealing with, just looked so intimidating, you know?

Take care Steve, Bill

 

[66Sprint]

I DO know!...Actually, I need to space the rotor out towards the fork 2mm of the 3mm clearance I now have so the caliper and brake pad bottom edge will clear the spokes... Talk about tight fits!......Steve

 

[66Sprint]

Update:
Fabricated the rotor spacer plate today using only a drill, sabresaw, some files, and appropriate measuring/marking tools... (sharpie, rule, dividers,centerpunch).... Invested lots of time, NO money..... What do you think?....

This just shows what can be done with basic tools, and some effort...... Machine shops are great, efficient, and expensive, so I do whatever I can without them..... LOL..... Steve

 

[tbpmusic]

Steve -

Your "machine shop" is about as well-equipped as mine !! :roll: :roll:

Think about what I used to set up my frame and geometry.
(plumb bob, string, tape measure)

bill

 

[66Sprint]

Bill, Yep, but your frame/wheels ARE properly aligned, and my spaced-out rotor now allows the caliper to be installed....... Like you, I go by results, not by the $ amount spent to get there..... Steve

 

[66Sprint]

Note.....
The apparent 3mm clearance I had was in small part due to mocking -up with the 12mm axle in the 15mm wheel...... I actually have less than 1/2 a mm clearance in the assembly now that the "correct" size parts are mocked up......I'm talking feeler gauge size clearances....... But it DOES clear!.....Whew! :roll: ....
Interestingly enough, the left side actually accepts a stock size speedo drive (it is now spaced correctly for one with the wheel exactly centered in the fork).... Now I just have to find one originally FROM a left hand side so it rotates in the correct direction... One from an 18" Yamaha wheel should work if the depth is the same as the Honda unit,(same ratio), but in my efforts to keep it basicly Honda, I'll have to find out if some Hondas used left side drives on disc wheels.... Back to scrounging parts!... To be continued...... Steve

 

[66Sprint]

Well, The "Comstar" equipped bikes do have a left side speedo drive..... Unfortunately, the central "tube" that actually spaces the wheel is 4mm longer than the old style drive, at least on the example I have, which (also unfortunately) is from a 19" wheel (different internal gear ratio)..... It will however be a good "practice piece" to figure out the best way to cut that 4mm from each of three separate areas.... The "center tube", the "engagement dogs" on the gear itself, and the housing (where it sits in the grease seal).... This would present no problem IF I had access to a milling machine, but I'll have to attempt it with hand tools.... If it works, I should be able to simply swap the gearing from an 18" wheel drive right into it (when I find one).....

Wish me luck!.... Steve

 

[66Sprint]

DARN!.... The CB400 uses a 19" wheel as well, so the internal drive ratios will cause the speedo to read faster than the bike is actually traveling (if I put it on an 18" wheel)......

ACTUAL EUREKA MOMENT....Those who have previously read this post will notice my speculation of a possible cure is gone...... That is because I FOUND the way!.... Admittedly, I now also have to join Bill in the Dummkopf Group, because the answer was right there....so obvious I consistantly overlooked it......
All I have to do is reverse the shaft (wormgear) direction within the drive unit which only entails some changes to the housing.....(so I can insert the cable from the opposite end of the shaft "tube"), and when the drive is placed in its normal position ("tube" beneath the axle albeit on the opposite side of the wheel) it rotates in the appropriate clockwise direction.......

I know I am posting EVERY tiny detail of the problems/possible solutions incurred during this modification, but I thought it might inspire or instruct those who are contemplating ANY type of changes to their bikes...... If anyone objects to my excessive posts, please speak up....I don't want to be obsessive about it (even though I am)....

Remember ANY change requires AT LEAST one other change to the affected system to maintain mechanical soundness, efficiency, accuracy, or safety .... I've been swapping parts for over 40 years, and still have to think it through every time...

But I do end up with some pretty interesting and unique bikes.....
LOL... Steve

 

[66Sprint]

Here it is!..... The part of the conversion that had me stumped for awhile, and ultimately won me the September "Homer Award"..... Top image is the stock right-hand speedo drive (minus the end cap which became the second bearing on the modded drive)... Bottom unit is my conversion for left-hand side of the wheel usage.....

The internals are from a CB360, so it should read correctly on the 18" CB200 wheel....Not quite as compact as the stocker, but not too bad either, and it works!....
Steve

 

[66Sprint]

Update:...... The final pieces of the project are being fabbed up...The caliper carrier bracket/torque stay mechanism...... The pivots and spacers have been carefully cut, filed and dressed to size and the "blank" plate is roughed out (6 worn, broken and bent sabre saw blades) and the drilling, filing, tapping, and welding will hopefully be finished within a few days (gotta work on my projects between "real work" and the proverbial "Honey-Do" list)......So it might take a full week....LOL....
I ultimately settled on a steel to steel bushing, but added a grease zerk to keep it mobile..... If it works as designed/intended, the unit might be able to mechanically reverse the load on the the forks internal shocks when the brakes are applied acting as a very rudimentary "anti-dive" system as well........ I'll post pics of all the parts as an "exploded diagram" as well as an assembly in place on the forks when it's done.....
Steve

 

[Guest]

how much clearance do you have between the caliper and the spokes?

I've noticed spoked wheels flex under cornering side load in my race bike up to 2 mm (yes, they started rubbing in a turn and thankfully not enough to lock up) now I run them with at least 4mm clearance. may not be as critical on a street bike but if you hit a good pot hole the results could be painful.

 

[66Sprint]

First, THANK-YOU for your comment and suggestion.... It is through the exchange of ideas that we ALL learn ...... I try to post each step and the considerations that led me to take the step in HOPES that someone else will either concur with or strongly disagree with my reasoning and logic.......Either way, MY project benefits from the additional input and ideas.......

I currently have only 1.3 mm of clearance, but it is at the "head" end of the spokes right at/near the hub, where the spokes are somewhat motion restricted..... I did take into account that the wheel could flex sideways when cornering, but that is usually more problematic under heavy side-loading and as one progresses outwards towards the rim..... with such a small, lightweight (and relatively slow) bike, the amount of possible side flex should be relatively inconsequential.....It will also be signifigantly less at the 3.5" outside radius of the rotor than it would be at the 9" radius of the rim edge.... I am additionally benefitted by the heavier gauge spokeing used on the CB200 wheel as it will be more resistant to flexing than the thinner spokes from the original wheel......
I DO intend to "shave" the caliper to achieve a minimum of a full 2 mm of clearance throughout its "sweep" of the wheel ( some areas of the caliper currently have more clearance), and I intend to remove as much as necessary, but little as possible (so I don't endanger the structural integrity of the caliper itself)...Normally, I would just space the rotor and caliper outwards, but these forks won't allow me that option...
Interestingly, the clearance IMPROVES as the inner "pads" wear, so it may be advantageous to "mill" them a bit thinner to begin with....(just a thought).....

As always, your comments are appreciated and requested.... I will NOT take offense if you think my project is stupid, or worse, dangerous....Please tell me so, just do it nicely... This is NOT flamage,..... It could save me from serious harm test riding my concoctions...... However, I am fairly stubborn (read "stubborn" as "anal") about my projects, and may (read "may"as "will probably") proceed anyway...

You have MY permission to say "I TOLD YOU SO" should the occaision arise, but ONLY IF you advised against what I was doing/going to do....

Thanks again, Steve

 

[66Sprint]

Update:
As is usual in my "trial and error" projects, some minor "adjustments" had to be made as I progressed...... The brake and carrier unit is coming together nicely, but the "anti-dive" part of the mechanism that eliminates the "torque stay" has required fabrication of an excentric "guide" for the roller bearing "caster" wheel......

Now that I have your attention, (well, the attention of SOME of you), let me explain how I intend this to function....... So hopefully, someone will either agree it COULD work, or tell me why it won't..............

First, Hopefully I can generate a mental picture of the assembly as it now is, and you can "see" what I'm doing, and why/how I'm doing it THAT way....

READY?...(There will be a quiz, spelling counts!).... :lol: ...LOL

OK Then.... Picture a capital "Y".... The axle pivots at the juncture of the three lines, the caliper is supported by the "top" V, and the bearing acting as the " castor" is at the very bottom of the base of the Y......AND, the "Y" is lying on its side....
When the wheel "bumps" upwards, the rockers carry the assembly upwards in an arc controlled by the length of the rocker...(length from rocker pivot on the "fork" to axle)... As this occurs, the "castor" (at the base of the Y) is pushed downwards by the arced "guide at the bottom of the fork, (which is "diving" in relationship to the axle) and since the whole assembly pivots on the axle, the caliper rotates up and towards the fork body. As the forks rebound, the rockers are pushed downwards by the internal shocks, and the castor is pulled back along the guide by a spring, returning everything to their "pre-bump" positions...... Nothing special SO FAR....

However, when the brake is applied, the caliper ATTEMPTS to rotate (CW)downwards with the rotor (disc) and transfers this loading through the leverage of the caliper bracket (the Y) to the castor....which in turn, exerts upwards force on the guide attached to the bottom of the fork pushing it up against the weight-transfer down force that would usually cause the front-end to "dive"...(hopefully minimising or eliminating the dive entirely)....

My fear is that the weight transfer force will act to "push" the forks down hard enough to actually rotate the caliper bracket counter-clock-wise..... And, since the rotor, (and hence the wheel) are essentially "locked together", this would actually push the tire CCW against the roadway, (essentially rotating it backwards) and cause a skid/slide/whatever you want to call it.......

I'm sure I can eventually find the correct lever-length ratios to prevent this, assuming I survive the "road testing" trials.... To this end, I have decided to "save" the C 200 frame to restore for my daughter, and try it out on an old "trail 90" (actually a CT 200) that I was throwing together to "cow-trail" on the weekends...... Since the CB 200 wheel is an 18 (rather than the stock 17") AND it has a larger tire, I'll probably have to remove the front fender as well......
Here is the partially assembled sacrificial lamb.....(pic taken with stock wheel when it still was a "different and separate" project)

Please post any ideas, (or the formula to calculate weight transfer), or comments....

Thanks, Steve

 

[tbpmusic]

Yer' makin' my head hurt, dude.

 

[66Sprint]

Bill,
It makes MY head hurt too....

But the idea that the torque force of the wheel/rotor transferred to the forks to slow or prevent their "diving" is SO simple, it would almost HAVE to work......If it does NOTHING more than prevent the (dreaded) link-fork "POGO" effect, I'll be satisfied.... I actually expect that this is all that will happen....The initial rotation of the wheel/caliper/bracket will "lift" the forks and "lock" them at full extension, essentially creating a "rigid" (hence non-diving) front end... (This would be great on a perfectly smooth, flat surface, but most roads aren't......) The entire weight of the bike and rider is pivoting at the rear axle, transferring forward as before, maintaining traction at the front wheel, but now it COULD be so great as to cause skidding.... (NOT the desired result).......However, .... as the wheel stops rotating, the force applied to the fork bottom to hold it upwards lessens....allowing the forks to "compress" (allowing it to "dive", but slowly and in a theoretically controlled manner)
I've tried to calculate the appropriate lever lengths for the carrier bracket based soley on the bikes laden weight, and the leverage that weight would generate at the link pivot with the lever pivoting at the rear axle..... I'm sure that it is somewhat more involved than that..... Nonetheless, I tried to "adjust" the bracket leverage lengths to SLOWLY (hopefully) allow the forks to "lower" (as opposed to dive).....
Success will probably be a matter of repeated testing with MANY possible variations of carrier lever lengths......

BUT, That's the fun....Playing with an idea until it works, or fails beyond fixing.....

( I'm likely to end up with a 90cc bike that does "stoppies"...OR, to have put a hundred hours into a mechanism that has absolutely NO discernable effect or benefits.....Wonder if that's hare-brained enough for a repeat "HOMER".....Surely this is not an original or "new" idea.....Someone has probably already tried {and failed} at this before.... Therefore, I nominate myself for this months' Homer [again]...)

Wish me luck!.......
Steve