‘79 Kz650B - Semi-Trackbike Build

On to the lower triple. The Zx6r clamp is a bit thicker than the 6E clamp. This means that the stem needs to be pushed further through the R’s triple to have the same bearing journal exposed. In this scenario that means the R’s triple needs bored 3.5mm deeper.


I finally ordered a boring head for my mill and couldn’t wait to use it.



I popped the stem in the freezer overnight to chill a bit. I don’t have a press so I used a BFH and a piece of alumiyummy bar to protect the stem.



And voilà!




Next stop is conversion steering bearings, fork stops and gauge mounting solutions.

Later, Doug

I cleaned up the rotor side of the rear wheel. Started with a buffing pad in a hand drill. It was the wrong item for the job so I finished cleaning and polishing it by hand. 40mins later and it’s not perfect but definitely more presentable.



I had a Driven 220mm wave rotor left over that I’ll be using. And I found a fluke of a deal on a brand new Vortex aluminum sprocket for $14.54 on Amazon!! I need to find some prettier 3/8-16 fasteners for the sprocket side. The current ones are yellow-zinc plated and look like they came off a farm tractor.




Lastly, I thinned down the LH spacer that came with the PM wheel by 3.5mm. The wheel slides in perfectly and without slop.







Later, Doug

I rolled the 650 backwards onto my lift and started disassembling the front end. It took me about 30mins plus another 10 to knock the old bearing races out.




I made some mockup steering bearings using some Delrin. It’s not cheap but easier and quicker to machine than aluminum.



Next up was installing the triples and lower legs. There are not a lot of threads exposed after installing only the bottom locknut. It will need massaging later but I can make it work. Plenty of thread protruding through the upper clamp though.




Back on two wheels.




Next stop is solving the steering stops. I can either use the Kz’s boss and add to the lower triple or use the lower triple’s lugs and weld a plate to the frame.



Later, Doug

Knocking down the frontend to-do list. Front fender, gauge mounts, steering stop, brake lines, and headlight mount remain, yet.



Since the front end is sorted enough to roll the bike, I spun it around so the swingarm swap can be tackled.





My biggest hurdle will be the swingarm pivot width. The Kz’s is 229mm….the Zr7 is 244. I drew up a diagram to help visualize things. It seems as if some sparks are going to fly for this.


Later, Doug

I see you got the "new bike motivation" you are making tons of progress! It looks like you are over-sizing the pivot bolt because if i recall correctly stock is 16mm - Thats well worth it as there is tons of slop there. When i did the oversize conversion I used an hollow axle from a Katana, cut it to length, and welded a stainless 316 nut on the end. really churches it up and weight savings to boot. IF you go this route make sure you use the correct filler rod for welding dissimilar metals.

I have gotten crazy deals on brake rotors on amazon before as well. I think it may have been an algorithm mistake or something because the price was being lowered a certain percentage each day I checked it, until it got down so low that EBC disks for KZs were $40. I bought several and sold them on ebay for $200 each, lol. Its rare to have a victory over our corporate overlords but its so damn sweet when it happens.

what tires are you planning on running?

doc_rot said:

It looks like you are over-sizing the pivot bolt because if i recall correctly stock is 16mm.

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Right now, I’m using the stock 16mm bolt. I machined another mockup bearing for the left side. The right side of the pivot is just slipped over frame boss. I’m still working out the details needed for the final design.

doc_rot said:

I have gotten crazy deals on brake rotors on amazon before…. EBC disks for KZs were $40.

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I scored those used Galfer rotors on eBay for $75/shipped. Sometimes it good to just randomly search keywords.

doc_rot said:

what tires are you planning on running?

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The wheels came with brand new Shinko’s. Not the greatest tire but they’ve never been ridden on, so they’ll work for now.

Later, Doug

its worth the hassle to go to 17mm pivot if youre going to ride near the limit. you definitely notice it when you hit bumps in a turn.

Just so you know, those front brake rotors are not legal for AHRMA Vintage Superbike, as they specifically rule out wave or petal rotors as not being period correct. They are legal for WERA V5.

ex119x said:

Just so you know, those front brake rotors are not legal for AHRMA Vintage Superbike, as they specifically rule out wave or petal rotors as not being period correct. They are legal for WERA V5.

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I figured since my wheels and calipers already rule me out of AHRMA, my component selection doesn’t matter much anymore.

To be honest, I’ll be lucky to make it to a couple track days a year..let alone run a full-on race even if WERA allows me in.

Later, Doug

doc_rot said:

its worth the hassle to go to 17mm pivot if youre going to ride near the limit. you definitely notice it when you hit bumps in a turn.

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Did you ream out the holes or just carefully drill them? I found the stock pivot bolt from my Gpz750. It’s 17mm but about 10mm longer. I remember replacing it with a hollow Triumph part. I’ll need to dig back through my records and see what it came from.

Later, Doug

I reamed them with a 17mm chucking reamer and did it by eye. It worked pretty well, I went slow and took the time to check it was in alginement constantly. On my KZ750 track bike i want to go 20mm, I may do it like a member over at KZR did, or i may completely remove the pivot and weld in a new one. Here are his pics that i saved as reference.

Warning…LONG 2-part post ahead.

Pulled the old swingarm out. Surprisingly, the pivot bolt slid out very easily. Just as I found on the web, the stock Kz pivot width is 229mm..


Knowing that I need to remove about 7.5mm per side, I cut about a 5-6mm sliver off of each side. This dimension, along with the saw blade thickness, gave me just enough material left to flatten and smooth out the rough edges left.





Then I turned up a left mockup bearing and a right side spacer since the Zr7 uses a 20mm axle compared to the Kz’s 16mm.


Time to slide the swingarm in to see if it would fit and if there were an interferences. The left side passenger peg bracket is close but has enough clearance.



I offered up the wheel to check for offset and the chain run. Turns out my right side spacer was ever so slightly long.




Went back and took about 1.5mm off the right side spacer. The tires aren’t perfectly aligned but “good enough for who it’s for” as my dad used to say.



A check to the chain line was next. It turns out my 5/8” offset sprocket is about 1/16” too far offset, which isn’t all that bad of a problem to have.



I threw the old chain on to check frame to chain, etc clearances. The 18T 530 sprocket is definitely the largest one that can fit. I’m going to have to remove the nuts for the footpeg studs as well as shorten the threads.



To be continued…

Later, Doug

Hung the shocks to looks at angle, lower mount locations…




And an obligatory 3/4 view.


Last thing was to check rake, trail, swingarm angle and wheelbase. With a 23.1° rake and the Zx6R’s offset, trail is around 95mm. The Zr7 arm is almost 2.5” longer than the Kz’s. This means the WB is 57” with the axle all the way forward. Swingarm droop is 7.5°. Note: all these numbers are with the rear suspension fully supported.




Later, Doug

Streetfighterkz said:

I figured since my wheels and calipers already rule me out of AHRMA, my component selection doesn’t matter much anymore.

To be honest, I’ll be lucky to make it to a couple track days a year..let alone run a full-on race even if WERA allows me in.

Later, Doug

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I get it and what you are doing looks great. If it ever comes to the point that you want to do an AHRMA event, you can always get a legal set of wheels and brakes. I used to do that on one of my FT500s. I ran 18" wheels for WERA V2 and 17" wheels for AHRMA. Since you can make up whatever spacers you want, another set of wheels would be easy. In the meantime, the PM Chicanes are awesome wheels for that bike.

Started digging around for more geometry information. Found a small nugget on AC Sanctuary’s website and another small piece of the puzzle on KzRider. These specs apply to the Z1/Kz900/1000 but the Kz650 is of similar design and geometry so maybe the same is applicable.



I put my shocks in the general location of where I want them and lowered the rear support that was holding the frame up. The bike sat on its own for the first time. This allowed me to find the true rake and get a close measurement for trail.






Comparing AC Sanctuary’s info and the FSM for the donor Zx6R, I’m sitting pretty close to where I want/should to be. I measured an offset of 42mm for the Zx6R triple clamps.


Later, Doug

I’ve been looking for a decently priced Zx6 fender. But there was only a three year production run, so just finding a fender is a little hard. Again, I rummaged through my spares and found a cut-up early Cbr900RR fender. I sat it on the tire and I think it’ll look fine, but will need a set of mounting brackets.



Next up was trying to come up with a mounting solution for the headlight. The Kz has ears that slip over the fork tubes and are sandwiched between the triple clamps. The Zx fork tubes are 41mm and not 36mm and along with different triple clamp spacing meant the stock Kz setup would no longer work. I didn’t like any off-the-shelf aftermarket solutions so I started thinking. I had a Kz900/1000 LTD headlight bracket for another project. It uses the gauge bracket studs to mount it to the upper triple. Unfortunately, when I held the bracket up to the forks in the approximate location, the neck mounted steering lock interfered with the bracket.

Next thought was a Zr7S bracket as Zrx owners use it for round headlight conversions so I found one. It uses the brake junction mount on the lower triple, but it wasn’t tall enough.




I had one last ditch effort before making my own was a first gen Ducati Monster bracket. I bought a used one from eBay and it showed up a couple days later. It’ll take a little bit of work but it’s more adaptable than the Zr7 part and is aluminum so it’s pretty light.





Later, Doug

Having found a headlight bracket, the mount for the bracket and gauges was up next. I started with a piece of 2x6x0.375” 6061 bar.




The Monster brackets uses a couple pins on the upper triple to locate it. I didn’t want bolts showing so I blind tapped some M6 holes and threaded in some 16mm long set screws.




Knowing that the new bracket may work, the rest of the Zx ignition mount had to go. After a trip to the band saw, followed by a belt sander, followed by some files, and finally followed a mouse sander and I had a smoothed out upper triple.



Later, Doug

Continuing where I left off… (Long post ahead.)

I took care of the headlight bracket part of the plate, so next up was the gauge mounting portion. Some drilling, some boring, some shaping, and sanding and the plate was finished.






Now on to the gauge mounting. The stock triple has a couple rings with a taper on each side for cone shaped rubber spacers.


Cut four pieces of 1” diameter aluminum round bar and started making swarf. I made the bushings so there would be a small gap when the two steps are 3/8” apart, which happened to be the thickness of my mounting plate.






I did a quick test fit on the gauge bracket with the rubber cones and it looked like they’d work.



I made the bushings so they’d be a light press-fit into the plate, so welding wouldn’t be needed.





To be continued on second post…

Later, Doug

And finished!






And with the headlight bucket held roughly in place.


Later, Doug

Not quite how I would have done it, but it does look much more professional without the hose clamps, safety wire and zip-ties that I would probably have used.
Nicely done.