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Discussion Starter · #1 ·
Just finished this swap on my 2018 Ninja 650. Used a complete front end from a 04 zx6r. I did the swap differently than any other builds I've seen. I went down on the bike and decided since I was going to have it all apart to check the forks that I might as well upgrade since zx6r front ends are cheap. The 650 forks were straight and ended up selling them for $250. Putting my total for this swap at $150~ including new fork seals and new fork oil

My build retains these stock parts and has the same ergonomics of a stock 650, just better forks/handling
-ninja 650 fender
-ninja 650 wheel and wheel bearings (wheel isn't machined for the bigger bearings)
-ninja 650 axle
-ninja 650 handlebars/riser/controls

PS. This is not a bolt on type of build. I did a LOT of cutting, grinding, welding and fabrication to make everything work. It's possible to do this swap more easily but at the cost of not retaining the stock ergonomics. I recorded some videos too. Need to edit them and put them up on youtube
 

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Discussion Starter · #2 ·
Step 1 was to get the top triple clamp situation figured out to retain the 650s handlebars. I shaved the ignition holder to give it a cleaner look. The steering stops had to be cut off to fit the 650s risers/handlebar holder. A lot of grinding and cutting happened on this piece to get it looking good and functional. If you locate the risers correctly you can just clear getting a screwdriver on the fork adjustments

The 650 riser has long bolts that go through bushings on the stock upper. Obviously the zx6r doesn't have those holes of bushings because they come with clip ons. The inside edge of the holes for the forks match up damn near perfect so its pretty easy to line up from side to side where the holes go. The harder part was getting them even on both sided front to back. It was about 1/8" off so I had to oval out the right hole a tiny bit to get the bars even.

Here's the video
Only thing it doesn't show is the setup for bolting the risers on because I hadn't got the far yet and forget to record it lol. I'll edit the post with pictures later.

You can see in the video that the riser has long bolts but only a small portion of it is threaded on the end. I found 3/8"threaded collars at home depot that worked great (always forget the actual name). I drilled out the center of the collars to fit over the riser bolts and cut them to the right length. Be aware that you need to cut/grind a good amount of extra stuff off the bottom of the triple clamp for these collars to slide onto the riser bolts. Once that is all done I cut 1/2" washers to make spacers that go under the collars. Might have been unnecessary but now they are sitting against a flat surface instead of the curved underside of the triple clamp. Look at the pics to understand what I mean
 

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Discussion Starter · #3 · (Edited)
Next up is figuring out how to mount the wheel. My goal was to use the 650 wheel, wheel bearings, and axle. Most people machine the 650 wheel to fit the bigger zx6r bearings but I didn't like that idea. Not sure if the 2016 and older 650s have bigger hubs but the 17+ wall thickness where the wheel bearings go in is 5mm. In order to do the bearing upgrade I'd have to pay/wait for a shop to do the work and cut that wall thickness in half to 2.5mm.

My first idea went terrible hahaha. I destroyed a 650 and zx6r axle in the process. I wanted to try cutting the threaded portion of the zx6r axle off and mounting/welding it to the 650 axle. So I cut the piece I wanted off and cut the 650 axle to the correct length. Turns out, if I did that the axle would be stuck on the wheel and I wouldn't be able to remove the wheel from the right fork lol so scrapped 2 axles and my time.

While fiddling I found out that the 650 axle is 20mm in the center but 25mm on the section that goes through the right side fork. That means the zx6r wheel spacers fit it perfectly. Ordered a second set of the zx6r wheel spacers so I had 3 of them to use. One gets used on the outside of the right fork, one goes on the inside of the right fork, and the third gets the lip cut off and welded to the inside spacer. I did this because the 25mm diameter section of the 650 axle isn't long enough to reach the inside zx6r spacer. Welding the 2 together keeps the center spacer from being able to float side to side and also supports the axle inside the fork better. This takes care of the right fork for the axle.

I need to record a new video to show the axle setup. I have several videos that show different attempts at making this work haha. Will be more clear to understand if I make a new video.
 

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Discussion Starter · #4 ·
Now for the left side of the fork to mount/tighten the axle.

I used a combination of the zx6r axle nut and special size nuts I ordered from Amazon.

The 650 axle thread is m20x1.5. The nuts I ordered look like steering stem nuts and came in a four pack (only used 2) for $11. They aren't very deep so that's why I decided to use 2 of them. Wanted the extra for more threads to grab with the axle.

The best way to do this is grind down one of the nuts until it press fits pretty tight into the zx6r axle nut. Put the spacers and axle from the previous step into the right fork and put the zx6r axle with m20 nut into the left fork. Wrap the axle threads so weld/spatter doesn't damage them. Thread the axle into the nut so its lined up and threads in and out easy. Now tack weld the m20 nut to the zx6r zxle nut. Take it all apart and weld it the rest of the way being careful not to weld so deep into the thread of the m20 nut. Now grind the weld flat.

Take the 2nd m20 nut and grind it down until it will slide in and out of the hole for the axle nut in the fork! If you don't do this before welding it together, you'll have to grind it down while its stuck on the fork. Ask me how much of a pain in the *** that was with a dremel..

Now your nut is ready so put the axle/spacers/nuts together again. VERY IMPORTANT to do in this exact order. Thread the 2nd m20 nut on the axle and then thread axle into your zx6r nut that has the first m20 nut welded in it. Now spin the 2nd m20 nut until it is snug but not tight against the left side fork. You should be able to (and need to check) that the axle spins freely in both nuts while you hold the nuts still. If you skip this step, you'll destroy and strip the threads when you tighten the axle. Or your axle will get stuck in the nuts because they weren't aligned properly. If it doesn't spin smoothly trying backing the 2nd nut just a hair at a time until the axle spins smoothly. Once you find that sweet spot use a sharpie to mark both of them so you can make sure nothing moves and can easily line it back up. Now tack weld the 2nd nut to the zx6r axle nut in a couple spots. I'd recommend leaving the axle threaded in for less chance anything moves. For the 100th time take it apart and weld it all the way around. Grind the weld down so it slides through the fork again. Now you have a custom axle nut and spacers to mount the 650 axle inside the zx6r forks.

PS yes I know certain year zx10r forks use a 20mm axle which would avoid this whole situation. At the time of this build no straight sets were for sale within my budget. So here we are haha
 

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Pretty comprehensive write-up, thanks. For sure it will help other members contemplating a fork swap.
 
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Discussion Starter · #6 ·
Pretty comprehensive write-up, thanks. For sure it will help other members contemplating a fork swap.
Thanks! I haven't seen anyone do a fork swap with the stock axle/wheel/fender or use the 650 handlebars so figured I'd do a build thread. I'll record more videos and pictures tomorrow then finish the write up here
 

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Well done mate
I can see the passion you have for making it work. Would’ve taken some patience too.
I don’t quite get the whole front axle situation and how you solved it. If you had pics video I’d be keen to see?
 

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Discussion Starter · #8 ·
Well done mate
I can see the passion you have for making it work. Would’ve taken some patience too.
I don’t quite get the whole front axle situation and how you solved it. If you had pics video I’d be keen to see?
I edited post #3 with a video showing how I did both sides of the axle/nut. Hopefully the video is easier to understand since I show the actual parts.
 

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Discussion Starter · #9 ·
Now on to the brakes.

This step is pretty easy. I used the stock master cylinder to go with my stock handlebar setup. From what I can tell it's not possible to use the 650s calipers. They don't fit between the mounts on the zx6r forks so even the most complicated brackets wouldn't position them on the rotors correctly.

You need 10mm spacers to mount calipers because the 650 rotors are 300mm and the 04 zx6r forks were designed for 280mm rotors. I found 3/8" (9.5mm) height spacers at ace hardware in the fastener aisle and grabbed 4 of them. I used the stock bolts (m10x60mm length x 1.25 thread pitch). 70mm length bolts would be ideal but I haven't found a place to buy them for a reasonable price.

Next is brake lines. I used the stock 650 brake lines because my tokico calipers didn't come with lines. When you go to bleed the left caliper, you'll see it doesn't have anything to stop the line from spinning 360 degrees while tightening the banjo bolt. The zx6r line has a stop built on it vs the 650 caliper having it. So if you mix and match like me, you'll have to use a screwdriver or pliers to bleed it and keep it pointing where you want. Get someone to help bleed. Trust me you need 3 hands haha

You have 2 options for calipers. Tokicos which are cheaper at $70~ or Nissin which are $130+. Key differences to know between the 2.
Tokicos
-cheaper
-softer initial brake bite. lever pull starts soft and progressively gets stiffer. Still a big upgrade over the 650 calipers but a different type of feel.
-brake lines mount in the middle of the caliper instead of the top. This makes the brake lines 2-3 inches shorter. I compensated for this with fork height in the upper triple clamp and adjusting the routing of the brake lines. It can be made to work but it will make the lines seem to short.
-Overall these are great is you want gold painted ones, don't mind the softer bite, and want a cheaper budget. For the average street rider these are perfect.

Nissin
-stiffer bite from the beginning of the lever pull. These take braking to the next level.
-only come in black so if you want other colors prepare to paint them
-basically double or more the cost of Tokico calipers
-brake lines mount at top of caliper so stock lines will fit perfect
-Overall they are better for braking and feel, and less hassle with the lines. Worth the upgrade if you plan to do track days or very aggressive riding.
 

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Discussion Starter · #10 ·
I definitely skipped a step haha on how to mount the forks

The 650 and the zx6r use identical steering stem bearing and the bearing nut (goes under the upper triple clamp) is also the same. I used my 650 bearings and bearing nuts on my swap.

You do have to use the zx6r upper triple clamp nut because they aren't the same size. It's an oddball size of 25mm so can't just buy it locally either. Make sure the forks/triple clamps come with a nut or you order one so you aren't waiting around for 1 nut to ride!

Pretty much as easy as sliding the 650 parts out, swapping the bearing over and sliding it back in. Make sure to grease it up good and go through the shop manual procedure to tighten the bearings down. I will say it is a little bit of a pain to tighten the lower triple bolts with the fairings on. The zx6r bolts go in from the side vs the 650 bolts go in from the front Easier to remove the fairings while doing all of this.

I found that 12mm height of the fork sticking out of the upper triple clamp gave me just enough room for the brake lines with tokico calipers. It sets the bike at 1/2" off from stock ride height measured at the neck of the frame. The small difference isn't noticeable and doesn't effect handling.

You can see in one of the pics that the brake line is routed behind the lower triple instead of in front. This is the only way the stock brake line will reach using tokico calipers

While I had everything apart after test fitting I painted the triple clamps and lower section of the forks with some gloss black engine paint I had. Matches the rest of the bike much better than the bronze color they come in. Love how they turned out
 

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Did you measure your base height when you started?
I’d recommend that you have a read about the effects of rake and trail on a bikes handling.
A 12mm drop in the front is a lot steeper than stock height and can make the bike really unstable at high speed.
Basically it makes it more prone to head shake. Mine is also steeper(from memory only by a few mm) I didn’t notice much until I had a moment. After reading up on it it made me think twice about a steering damper.
I don’t want to take away from the awesome job you’ve done. A fork swap isn’t for the average person and if a finer handling bike is what you’re after the rake and trail is key.
 

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Discussion Starter · #12 ·
Did you measure your base height when you started?
I’d recommend that you have a read about the effects of rake and trail on a bikes handling.
A 12mm drop in the front is a lot steeper than stock height and can make the bike really unstable at high speed.
Basically it makes it more prone to head shake. Mine is also steeper(from memory only by a few mm) I didn’t notice much until I had a moment. After reading up on it it made me think twice about a steering damper.
I don’t want to take away from the awesome job you’ve done. A fork swap isn’t for the average person and if a finer handling bike is what you’re after the rake and trail is key.
After adjusting everything and riding for 600 miles the forks are at 1/4" or 6mm higher than stock. I could take up most of that by resetting the fork height and get it within 2 or 3mm if not the stock height. No issues with stability or wobbles up to 120mph
 

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Discussion Starter · #13 ·
A big thing to note about this swap!

From the first 600 miles of riding, 4 rides of that being hard runs on twisty roads, the front end feels great. Big problem is with the front set correctly, the back feels sooo bouncy when braking hard to corner. Makes the whole bike feel unbalanced. Imagine an old truck with worn out shocks how it bounces 2 or 3 times if you jump on the bed or bumper.

Temporary solution is setting forks at softest settings (still stiffer than stock 650 forks). Bike rides well set up like this. A decent amount better than stock.

Medium solution? I hear the 650 rear shock has some adjustability at the downside of having to remove the whole shock to do so. I'll do that when I take it out to measure it for a swap.

Long term solution is a rear shock swap which is next on the list. I would like to use an old zx6r shock since I can get that in the same gold as my front calipers. Depends if its similar length so we shall see
 

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There’s threads on here and in a lot of places about doing a rear shock swap.
I used an r1 and had to respring and revalve it.
Well done getting this far brother !
 

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Discussion Starter · #15 ·
There’s threads on here and in a lot of places about doing a rear shock swap.
I used an r1 and had to restring and revalve it.
Well done getting this far brother !
All the rear shock swap threads I saw were for 2016 and older 650s that have the shock on the right side not in the center like on the 2017+. They have different shock part numbers and different bushing part numbers
 

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Awesome, yours will be much more straightforward.
I haven’t seen anyone document a swap on those it’d be great if you could take lots of pics and measurements ?
 

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Discussion Starter · #17 ·
That's the plan. I'll make a new thread for that swap. I have to change fork seals and put new oil in so I'll take the shock off to measure it while the bike is down.
 
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