Easy USD front end for KR1/1S

[RickNC30]

I`m not sure if this has been suggested on here before, if so I`ve missed it -

A simple USD conversion for the KR1/1S is to use ZXR400`H` model yokes. These have the same stem dimensions as the KR1 and fit straight on using the standard ZXR bearings and seals - the steering stops are in the right position, the only modification required to fit later model fork legs is to bore the bottom yoke where the legs fit through from 50mm to 52mm - this is a half hours work for any competent machinist.

Once you have bored the bottom yoke you have a front end which will take either ZXR400L forks or, better still, the ones from a ZX636 B1H (2003/4) or C1H (2005/6) model which both use the excellent 4-pad Tokico radial brake calipers. The fork legs from the ZX636 are the correct length to match the KR`s chassis geometry.

The combination of components that I`m using in my build is C1H fork legs, calipers and discs with a B1H wheel (interchangeable with the later model) which is a 3-spoker and matches my RGV VJ22 rear pretty well. Handlebars and radial master cylinder are from a late model GSXR600 and I`ll be using the mudguard from a ZX-10R as it is smaller and less clunky looking than the ZX-6R unit. I have modified the forks to suit the lighter bike by changing the springs for stock RVF400 NC35 ones (which drop straight in) and the oil for 2.5W instead of 5W.





I`ll post more photos as I get further on with the build...

Rick

[JanBros]

it's been done before, and the yokes of the 400 have been discussed many times.
I to have ZX6 forks in mine.

but keep the pics comming, we love to see a built from fresh

[RickNC30]

OK, that`s good -

I`m fairly new here and the only one I had seen was using ZXR400 `L` yokes which required a lot of modification.

I`ll maybe put a bit of a build thread in the Projects section as I go along...

Rick

[JanBros]

at the top right, there is a search option. if you type ZXR400 yokes, you get 6 pages of search results

search.php?keywords=zxr400+yokes

[500bernie]

Hi Rick,
Like Jan says, keep the photos coming, and check the lock stops as most were modified to reduce the extent of movement.
Cheers
Bernie

[RickNC30]

Ref the lock stops, I have around 30mm clipon/tank clearance and it looks OK at this stage but if I find that there are master cylinder/fairing clearance problems later on I`ll just apply the usual solution by drilling & tapping the stop blocks on the yoke and fitting M6 bolts which will both reduce the lock and make it adjustable - I`ve had plenty of practice with this kind of stuff.

Hoping to have this chassis on its wheels over the weekend - need to get the 1S swingarm shimmed up correctly into the KR1 frame first, then I can finally bolt up the frame/suspension and move on.

[JanBros]

forgot to say : ZX6 springs are too stiff in a KR, certainly for road use.

[RickNC30]

You didn`t read my post carefully - I have swapped the springs for standard RVF400 ones which have the same dimensions as the ZXR springs but are around 0.7kg/mm instead of 0.9kg/mm. I have changed the oil to 2.5W instead of the standard 5W in the first instance but if that doesn`t work as well as I expect then I wiil get K-Tech to build me some custom valving.

[500bernie]

Hi Rick
I have NC 30 fork tubes and internals on my KR1S and they are great.
I have a comparison table of the NC30 and standard KR1S springs, I will see if I can find it.
Cheers
Bernie

[RickNC30]

Standard NC30 springs are progressive (multirate) with quite a soft initial rate which results in too much suspension travel being wasted in sag on the 400 but I imagine that they would work pretty well on a KR1. On NC30s I usually change them for single rate springs of between 0.8 & 0.9kg/mm depending on rider weight and usage.

[JanBros]

You didn`t read my post carefully

indeed I didn't

[kinkyfreestyler]

Like what you've done so far ,keep up the good work

I was intreasted in what your all saying about springs,I have fitted the zxr400l forks and found the springing way to hard ,after speaking to maxton they say the original fork carries a 7.5 rate spring and they have offered me a lighter rate to see if that helps !
So when I try them out (lets be honest ,it'll be spring ! before I can really try them ,wet roads etc.. ) I'll let you know the result !
I also dropped the fork oil weight and lowered the oil height by 15mm (about 30ml ) and that made a differance.

look forward to seeing your progress

[RickNC30]

Ref ZXR400L forks - I have used them on NC30s and in that context they are undersprung and have too much compression damping so you will certainly need to reduce the damping if you are using them on a 250. Increasing the air gap obviously reduces the pneumatic component of the fork springing so that will help. What weight of oil are you using now?

[RickNC30]

Continuing the build - we have wheels...!



The front is actually from a Hornet, simply because I had it in my spares stash, I already make an adaptor kit for it to fit the ZXR forks and it uses the same discs as the NC30. Powdercoating is the gold that Subaru use on Impreza wheels, done by Aerocoat (who also did the gloss black frame), discs are Arashi waveys.



Rear is a 17" RGV250 unit, fitted using an adaptor kit made to the spec that`s posted in the archive on here, Talon sprocket, wavey disc.



Shock is a Nitron R2, suspension linkage uses BDKs jack up arms. It`s probably common knowledge on here but fitting the 1S swingarm to the KR1 frame requires more than just boring the pivot holes for the larger diameter bolt. Because the KR1 uses metal cap type grease seals and the 1S doesn`t, you have to shim the ends of the bearing inner sleeve to avoid `squeezing` the frame when you tighten the pivot bolt (0.5mm each end did mine) and then shim the swingarm itself to control the sidefloat (1mm each end in my case). Shim sizes are 20 x 28 and 28 x 40 respectively - you can buy them on ebay from a supplier called `Screws City`.



The finish on the swingarm is vapour blasted and then clear anodised, which didn`t come out exactly as expected but I think I quite like it - it`s a kind of satin finish mid-grey, looks very like mag wheels do when they been stripped for recoating. Good BS potential, though - `nah mate, it`s the factory race kit magnesium swingarm...`

Now I just have to work out how to get it off that bench without giving myself a hernia...

[kinkyfreestyler]

I COVET THY REAR WHEEL

LOL