ZX6R Fork Conversion for Zephyr - Custom Triples

Some of you have been following my progress on this in another thread, and the mods have granted me permission to post this sale thread for the custom front fork conversion triples that I’ve been designing. 

A little bit of background and what I’m trying to do. It’s been a dream of mine to fit a set of upside down forks to my Zephyr 550, and when I got a second bike earlier this year I figured that was a good time to seize the opportunity for the project. So since about August, I’ve been measuring, 3D modeling, asking lots of questions, and prototyping with 3D printed plastic. While I still have a ways to go, it’s coming along very well. 
 

Rather than “off-the-shelf” custom parts, or searching every model of bike for a set of triples that would accomplish this, I chose to design my own for one simple reason: I want to use as many of my bike’s original parts as possible. I want it to look natural, like it was born that way. 

The forks are from an ‘03 ZX6R, and the brake calipers from an ‘08 Triumph Street Triple R. There are some details such as axle spacers and disc rotor spacers that I’ve also taken into consideration, designed, and prototyped. 

The reason I’m posting about it here in the for sale section is just to gauge interest. I am wondering if there is anyone else out there in KZR land that would be interested in having a set of these parts for their own bike. This isn’t me trying to make money, it’s me trying to save money. See, if I just go it alone and get a single set CNC machined for myself it’s going to be expensive. Estimates I’ve been able to get so far put it around $1000 just for the triples (which doesn’t include the other parts). But, if I double the quantity then the cost per set drops down to only $600. That price is a lot friendlier! Imagine if three people wanted a set. 

Additionally, a lower cost per set means me and the potential other buyers could explore some concepts to make the parts nicer. Filleted corners instead of straight cut for example. This might raise the cost again, but if we have enough “bulk” buying power we can still keep things affordable. If I end up only making the one set, they’re going to be pretty basic, but if a couple of us all want them, we could get fancier. 

Anyway, I hope that’s a good introductory post about the project, but do please feel free to ask me any questions. At this point I am not asking for any money, this is just an inquiry about interest. I just want to know if there is anyone else here who might want a set. The more of us there are, the more affordable they will be. But for now the closest (albeit very rough) estimation I have is that if even one person wants a set, they will run about $600. All I’m looking for at this point is anyone who wants to say “count me in as interested.” 

I wanted to provide some more details about this, in hopes of expanding the conversation about it, and maybe drumming up some interest. As I've said above, I'm really not making any money on this, it's just something I want to do, and I'd like it to be affordable. Perhaps if everything is successful I might consider another batch down the line as well.

Fitment/Compatibility

While I am primarily focused on making sure it fits the Zephyr 550 model, I believe there are other bikes these custom triples will fit. It is my understanding that the other Zephyr models, 750 and 1100cc models, all use the same steering stem, and should therefore be compatible. Additionally the ZRX1100/1200 models are also supposed to use the same stem. Clearly those are all bigger bikes that you might not want to use forks from a 600cc model on. However the triples will fit basically any fork with a 50mm top, and 52mm lower diameter. Granted this isn't the most common size, but I believe there are other forks out there that match that spec, including those from the first gen Z1000 ( at least according to some ). 

It should also be possible to extrapolate additional compatible models using the AllBalls fork swap finder . For example I just ran a quick search for the 1980 KZ650F1, and found that they have bearings to fit the ZR550 Zephyr front end, which leads me to believe that with a Zeph stem, and the triples I'm designing, you could fit ZX6R forks to that bike. Granted I'm sure all of this is easier said than done. But I feel confident that my research is sound, and with a little patience and elbow grease these things are possible.

Stem

Since I already brought it up, it's worth discussing the stem. My design reuses the stock Zephyr 550 stem, which must be separated from the stock lower triple. Because it is welded in, you must grind off the welds, and then press out the stem. Early in the project I had a friend do this for me. I had removed, and subsequently ruined the lower bearing to do this. However now that I am more intimately familiar with these parts, I believe it is possible and actually preferable to not remove the lower bearing. After grinding or filing off the welds, you would press the stem out from the bottom up (likely upside down in reality). The part of the stem left below the bearing is about 23mm, and this length bottoms out in the lower triple of my design, when pressed in. 

I have waffled back and forth about whether to make the press-fit part a true perfect tight fit, where a hydraulic press would likely be necessary, or making it 0.1mm oversize in the triple, which allows for a "slide-in with no wiggle room" fit. While looking for a good method to secure the stem to the lower triple, I found that a bicycle stem "star nut" could be installed in the stem, and using a bicycle top cap, the stem is bolted to the lower triple. Any decent bicycle shop should be able to install one of these nuts, though it should be noted that it requires the less common 1" size and not the very common 1-1/8" size. Currently this is how my design works, but I am open to making the adjustment for a regular press-fit if that's what potential buyers prefer.

Headlight and Gauges Brackets

This is going to be a long section, so buckle up. Because I am trying to retain so many stock components I have designed in all of the mounting points so that virtually everything can be used. I have two concepts I am experimenting with for this. The lower triple stays the same for both concepts, but the upper triple varies. In the first concept the upper triple is one solid piece. In the second concept, it consists of two pieces, the actual clamp which could be considered "universal" and a second piece which is bolted or glued to the first piece and holds the mounts for the gauges, ignition column, and headlight bracket.




These photos represent concept 1 (green). As you can see, it is similar in many respects to the stock upper triple, it's basically "plug and play." Obviously that is the major advantage of this concept, however the downside is increased manufacturing costs. I do not have exact figures on that yet, but again this thread is about gauging interest. If enough people want to go in on this together, maybe we can afford to go "plug and play" all the way.




These photos represent concept 2 (purple). The main actual triple clamp is a lighter shade of purple than the attachment piece. It is intended to be made with a CNC machined primary clamp, and 3D printed, or fiberglass/carbon fiber molded attachment. They could be joined together by either running a longer bolt through the handlebar clamps and affixing a nylock nut to the underside, or using a high strength adhesive. The first advantage of this concept is that with a "universal" top clamp, you wouldn't be locked in to only using the stock gauges and brackets. Custom 3D-printed attachments could be designed for mounting virtually anything, or the clamp could be used with nothing else attached at all, for a very clean look. Clamp a Quad Lock to your handlebars, use your phone as a speedo, and really go full minimalist. The other advantage to this design is that the cost to make the main clamp should be lessened. The attachment piece would be an additional cost, but 3D printing can be pretty cheap these days. And finally, the downside to this concept is that attaching the two pieces together by any means is not quite as nice and convenient as the "plug and play" ability of the first concept. I personally would prefer the first concept for my bikes, but I'm just trying to find ways of making this affordable for everyone.

One thing you'll notice about both concepts is a 10mm drop at the clamp. I wanted to make sure that the fork top caps do not touch the handlebars. As a bonus, this helps correct the steering geometry for a closer to stock feel, however extending the forks an additional 20mm is recommended for a full steering correction. You can see how to do that elsewhere on this forum. 

Lastly, I want to mention that the lower triple has a single mounting point for the Zephyr headlight bracket, but does not have a place to mount the stock brake hose splitter. Because the whole conversion requires the use of alternative brake calipers, you'll be running all new brake lines anyway, which means you won't need it. The headlight also needs a bracket fabricated for the angle adjustment. This is one detail I am still working out, but my guess is that if you are mechanically inclined enough to take on a conversion like this anyway, you will probably be able to figure that one out. I'll be sure to post about what I end up doing.

Wheel/Rotors/Speedometer Drive

For me, I'm trying to use my stock wheel, rotors, and retain the speedo drive, so there are a number of things to consider there. I have axle spacers, disc spacers, GSXR rotor bolts, and I still don't honestly have any idea how I'm gonna actually keep the speedo drive from trying to rotate on it's own. But those are all my problems to deal with and I won't bore you with the details, just say that if you want to discuss it we can. Why? Because you are probably smarter than me, and you will probably just use a ZX6R front wheel and axle and rotors and the stock brake calipers and everything will just fit. Swap in the rear wheel from the ZX6R as well, mount that wider rubber, and have yourself a little track day fun or something. 

TL;DR

Just some info, man. 

Fantastic work so far, the possibility of 750 and 1100 owners should make this popular. Well done. over 40 years now since i swapped front and back ends on my 400/4 for CB400N super dream parts. My days of this sort of thing are over but there must be plenty of folk with genuine interest and can make valid contributions.

regards

rob B (UK)

Bumpity bump bump.

Just wanted to see if I could get some more eyes on this, if there might be any questions or comments about it. I'm hoping to have them made and installed on at least one of my bikes by April, as that's when the 1 Moto Show in Portland is, and I submitted my bikes to be shown. I've been in contact with Cognito Moto about having them do the actual production, though no word yet about if that's going to work out. I mean it will, and I'll be using them for sure, unless they unexpectedly come back with a quote that's double what I've been getting from places so far. 

So yeah, anybody maybe thinking about it?

Project update. 
I’ve been busy with work and college lately, so I haven’t had much time to work on it. But I was exploring a few ideas I thought might be worth discussing. 

Spacing and Rotors
First of all I was considering a suggestion from Wookie about narrowing the spacing between the fork legs to make it so that I do not need to use spacers under the disc brake rotors. I went through a few versions of this, and found that 196mm is what it would be. For comparison, the stock ZX6R forks are 210mm, and my stock Zephyr forks are 205mm. 

I asked around about if such a narrow spacing would work, and didn’t get any replies. The idea has some other complications to it as well, so I’m thinking I might have to go another route. 

As such, I want to try and revise it to match the stock Zephyr 205mm spacing. I figure that’s a safe bet. This will of course necessitate a spacer under the disc rotors, unless I can find an off-the-shelf rotor that bolts right up and has a greater offset. The stock offset is 13.5mm, I would need 18mm. I have found it virtually impossible to even search for such a thing, as no rotor manufacturer lists enough information on their websites. 

Forks
I’m also exploring different fork options to see if some other fork besides these ‘03-‘04 ZX6R forks will be easier to work with. Non-radial brake mount forks might make it so that I only have to design an adapter to move the brake caliper in closer to the wheel (basically just a wider adapter than what’s already there), rather than shim the rotors. 

Wheels
I am of course also looking into options for other wheels that might make things simpler. It might be nice to find something that would let me swap both front and rear wheels and take advantage of wider, modern rubber. The challenge is that I really like the five-spoke design of my stock wheels. There’s maybe the Zephyr 750 three-spoke wheels, which would at least still be in the Zephyr family, but there’s not much else that wouldn’t look out of place. If money were no issue I could get some Galespeed or Marchesini wheels or something, but they are very expensive. 

—-

Thats all for now. I haven’t given up, but I will admit that all the complications are a bit disheartening. I knew this would be difficult and potentially expensive, but now its also taking so much longer than I thought it might. 

On the plus side, I recently acquired a 3D printer of my own to make prototypes with. It was free to me, other than buying some PLA filament for it. So at least after I get the hang of using it, I can make my own prototypes for a lot less. 

You appear to be going down a "rabbit hole" with this. Mixing and matching parts will always come with challenges (otherwise everybody would be doing it) from what I can see going with the 205 spacing and 4.5mm rotor spacers is "the compromise" if everything else works. If you start introducing more variables with different forks, wheels etc then the whole process starts over again as this will inevitably bring different chanllenges. I think you will struggle to find rotors with an 18mm offset (my ZX9R Rotors only have 11mm)
I would settle for the 4.5mm rotor spacers, draw a line in the sand and move forward 

 
I haven't given up yet. While this rabbit hole may be deep, somewhere in here is a door and a golden key. 

Fork spacing.

I've landed on 205mm for the fork spacing, which is exactly the half way point between the stock Zephyr 200mm and the ZX6R 210mm. You gotta love a nice happy medium. This makes mounting the triples with the stock gauges and bracket pretty much plug and play, as any narrower and the bracket gets difficult to fit. I am still considering taking a few millimeters out of the offset in order to help correct the steering geometry that tiny little bit more, and making space in a tight spot behind the headlight ears.

Disc Rotor Spacers.

With this fork spacing the disc rotor spacers should be 4.5mm thick. I have designed this part, and submitted it for quotes at a few places. The only place I've got a quote from so far says it will be about $204 for a pair.

Axle.

Perhaps the most interesting development in this project is that I managed to acquire a conversion axle from SPEC Engineering Japan via Webike.


First I want to say that it is a very nicely made part. The machining is beautiful. But, it isn't a perfect fit for me as is. Most notably the left collar is off by about a half mil to get the proper spacing when tightened. Additionally the flange on the outside is too big. I also don't love that there is no flange on the right side collar, but that I think I can work with (more on that later).

Here is what the left side collar looks like in CAD:


I thought about having that part modified to work, but it would take quite a lot of precision to do it right.

So I decided that maybe designing my own left collar would be the way to go. Here is my design:


This ended being a fun project, because I actually learned a lot about Rhino (my 3D CAD software) in the process. 

I've got this new axle collar uploaded for machining quotes, and the one that has got back to me so far has it at $125 in 6061-T6 aluminum. My understanding is that would be a good material choice, but that the axle torque spec would be 60nm, instead of the 88nm my stock all-steel axle has. I am interested to hear thoughts and opinions on that. I think it would be lovely to have the part made out of 4140 steel instead, but with heat treating it would be over $500.

On either the Zephyr or ZX6R stock setups, the wheel is centered by the collar flanges, one on each side. When the axle is torqued to spec there is no side-to-side movement, and then when the fork lower pinch bolts are torqued, the axle is no longer able to rotate. With this design the entire assembly indexes and centers off of the left hand side, since there is only the one flange on that side. However I believe that once the left collar is in place, and measurements have been made to ensure it is fully seated where it should be, that the fork lower pinch bolts could be tightened, and then the left collar need not ever come back out again, lest it should get damaged for some reason. The design allows for relatively easy wheel removal without the need to remove that collar, so I think it should be mostly a one-time installation. Again, I would love to hear anyone's thoughts on that. 

At this point the design is getting very near final, and I've done almost enough prototypes to say it's good and solid. I'll probably do one more round and full mockup on the bike, just to be sure, but it's finally starting to look like the home stretch.

Love the detail you are going to with your thinking on this but I think you are in danger of "loosing your mind". The wheel is centred by the speedo drive on the left and the spacer on the right (both sit against the inside face of the fork and the corresponding wheel bearing) tightening the axle nut then ,tensions the whole assembly. As long as your sleeves don't protrude inside of the face on the fork and foul the spacers  they will be fine and won't effect "centring" of the wheel.

Ive made several custom axles for various bikes over the years. heres some thoughts on your solution:

The correct method of axle installation is: torque axle, clamp one fork on axle with pinch bolts, cycled the suspension several times to seat the opposite fork leg, then tighten pinch bolts on that side. you want the fork to find its home on the axle, this can vary slightly. Not having a flange that traps the fork leg is on one side is of no consequence and can even be ideal due to machining tolerances, you don't want to bind the fork in any way. You can include a flange for cosmetics but leave a small clearance to the fork.

Do not go with an aluminum axle - there are several reasons most racing organizations have banned them.

The axle assembly needs a minimum clamping force to function as a structural member of the fork assembly. This is extremely important. You're proposing a 32% reduction in clamping force, while you have simultaneously increased the span that you are clamping. Look at the torque spec for the axle of your donor forks its likely higher than the stock ZR. Ideally you need to be increasing clamping force and rigidity to compensate for this increase in span. Consider over-sizing the axle, this will help deal with the increased torque and will increase rigidity. Since these are upside down forks the axle is all that keeps the fork lowers moving together. Having a robust axle is more important on an upside down fork application because you can no longer use a fork brace as you would on a conventional fork.

4140 does not require heat treatment for this application and would be a good pick because it is a relatively rigid material. heat treating makes the steel harder and stronger but does not increase rigidity. Hardness & strength do not equal rigidity. You want an extremely rigid axle to keep the fork lowers moving together, it doesn't mater so much how strong or hard it is. www.accu.co.uk/p/111-strength-rigidity-hardness-difference

If you must go aluminum axle use 7075-T6 but I would look at this as a last resort. the nuts and sleeves can be 7075 as this gets pinched onto the steel axle. Also 7075 will resist corrosion much better than 6061.

If you're going to go with a custom axle - oversize it if you can. That appears to be a 17mm axle, there likely are bearings out there to allow a 20mm axle. Ive done this on my KZ1000. it will require a new internal bearing spacer.

My preferred method for making custom axles is to use an axle from an existing bike. I have used GSX-R and Katana axles as they come in 20mm and 17mm and are hollow - weight savings is desirable in this application and a hollow tube has the same rigidity as a solid bar -all else remaining equal. I cut off the un-threaded side of the OEM axle and weld a stainless nut or sleeve on the end. Use ER309L for welding dissimilar alloys  - in my case  stainless 312 nut to some type of high carbon steel axle. I then chuck it up in a lathe to ensure the clamping face of the nut is perpendicular to the axle shaft. you need a washer with a large chamfer to clear the weld on the inside of the nut face. You can either use the factory nut with the axle or make a custom one out of 7075. anything that gets clamped needs to be a tight tolerance to allow clamping forces to translate though the aluminum to the axle. Sometimes I will slit the collars to make sure that 100% of the clamping force is hitting the axle.

keep in mind you need some clearance on the axle to the bearing. typically a 20mm ID bearing will have a 19.85mm OD axle

heres a couple axles I have made over the years




 

Very informative posts! I will respond to these in more detail later when I’m out of class, but I want to clear one thing up real quick. 

The axle I’m talking about using is the SPEC Engineering axle pictured above, and it is steel. I think it might even be chromoly. The only part I’m asking about making from 6061 versus 4140 is the left side axle collar. Good to know that I don’t need to worry about heat treatment if I go 4140, that’ll only run me about $225 instead of over $500. 

I will do some research on larger axles and bearings that might fit them. 

Again, thank you for the replies. Here’s a few additional thoughts. 

Regarding my comment on the axle torque spec, I was referring to a difference in torque based on whether the left side collar was made from aluminum versus steel. From what I understand, and correct me if I’m wrong, but you simply can’t torque as high on an aluminum part as you can steel. My axle instruction manual is in Japanese, but it does clearly state 60nm with the included collar, so that’s where I got that number. I assume that if I spend the money to have my custom collar made from 4140, I should torque it to 88nm as recommended in my manual. 

I do see your point about a larger diameter axle. The stock Zephyr axle is only 15mm. I have been searching for a while now about how to simply use the stock ZX6R 25mm axle, but it becomes a matter of swapping bearings in the wheel. So far I have not been able to find a bearing that will simply swap straight in and is rated for the application. Perhaps I need to learn more about bearing loads. What I have found is a bearing from a Yamaha that is 4mm narrower. Presumably I could place a shim behind them, find or make a new spacer (the tube that goes between the bearings inside the wheel), and I’d be in business. The speedometer drive from a ZRX would fit in the left, and again find or make a spacer for the right. So these are options, but I don’t know what the best course of action would be. 

I could also swap to a larger axle besides the ZX6R. A little research reveals that a Ninja/Versys 650 uses a 20mm axle, so I could get my hands on one of those and design around it. Interestingly, I’ve found that the ‘04-‘05 ZX10R also uses a 20mm axle, and has upside down forks that otherwise look almost exactly like the forks I have. They use 300mm rotors as well, so perhaps getting a pair of those would be a good idea. Redesigning my triples for the larger lower clamp diameter wouldn’t be that hard. 

I think what makes all of this so challenging is that I’m set on using my stock front wheel. Most modern bikes use the very common 120/70-17 tire size, and fork spacing ends up at 210mm. My tire is 110/80-17, and stock fork spacing is 200mm. So that extra 10mm difference in width translates to complications in multiple areas. 

I had previously misunderstood what you were asking, I thought you were asking about an aluminum axle, when you were asking about an aluminum nut.....

 But lets back up a bit here.

Application is everything. A ZX6R is a proper sport bike of its era. Its designed for sticky tires and track time. This is where a large diameter axle will really make a difference as the loads slicks and high cornering forces of racing on a track are nothing like what you will see on the street. In reality -  how are you using this bike? mostly city riding with some highway? potentially some spirited riding on a windy road? Arguably the 15mm axle is adequate for that application - the ZR550 was never a sport bike and likely will never be ridden as such. being realistic in what you expect to do with it can save you alot of headache.

The smart thing to do would be to run the axle as is and see how it works, if necessary modify from there. Still torque to the factory spec. If you strip the threads, get a new nut machined. Once its torqued and clamped it will not strip so as long as it can take the inital torque you will be OK. if the nut can't take it, you need a new nut. Repeated installation and removal might be where problems arise - there is finite amount of times you can tighten and loosen fasteners and this is a lot lower with aluminum. I would not sacrifice the OEM torque spec on that bearing assembly especially with the USD forks and wider span.

Now that being said, if you're looking for an engineering/design exercise (which I personally enjoy) and want to get into the nitty gritty -  there are other options. 20x42x12 is a fairly common bearing size. space it out with a bushing on one side and a longer bearing spacer, or forgo that and make custom spacers. The sky is the limit on what you can change, hell you could have the wheel bored for larger bearings. The caveat being you are a student and since you are not making your own parts this shit can get expensive.

Have you considered getting a lathe? This is a cheap chinese import but I have personally used lathes similar to this and while they are crappy little machines you can make nice parts with some patience and careful use. Manufacturing your own parts is the only economical way to mess with stuff like this. Ive seen these go for $300 on craiglist/facebook
www.walmart.com/ip/VEVOR-Metal-Lathe-7x1...vable-Lamp/971706705