KR1-S Cartridge Fork Conversion

Wheels, shocks, forks, frame
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Mohawk
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KR1-S Cartridge Fork Conversion

Post by Mohawk » Mon Jan 18, 2016 2:37 pm

I've just converted my KR1-S forks to cartrige type with rebound damping.

Unfortunately I forgot to take pictures, but the process is fairly simple, but I had all the parts lying around, so decided to give it a try. So here's how it goes.

(EDIT - Jus found this, has some pics viewtopic.php?f=11&t=12896)

I used VTR1000 chrome stanchions, caps & cartridges, which I had left over from another project. I also used VFR800 springs & valves to get better damping rates & fitted these to the VTR1000 compression rod to add rebound adjustment.

There are only 2 issues with this setup & that is the h***a cartridges use a M8 bolt to secure them to the base of the lower alloy slider & the KR1-S uses a larger steel bolt (M12 ?,I didn't measure it) that screws into the steel at the base of the damper rod. The second is that the h***a cartridges will NOT fit through the KR1-S stanchions, its close & they could be bored out but that is NOT reverable & the inner bottom of the KR1-S stanchion is deeper than the h***a's, so would lose wheel travel.

To get past the 2nd issue, just use h***a stanchions, I had these to hand, so no cost to me.
As an FYI the fork caps are interchangeable, I tried KR1-S. VTR1000 & VFR800 caps all fitted the chrome stanchions !

To deal with the 1st issue, I turned the KR1-S bolt threaded area down to 8mm, then cut an M8x1.25mm thread on it, this allows the KR1-S bolt to mate to the base of the h***a cartridge.

Both the KR1-S & VTR1000 springs are too soft for me, so I used a spare set of standard VFR800 springs & spacers I had lying around, these work out to be the perfect length to fit this hybrid fork, with KR1-S bottom & VTR1000 top stanchion. My thinking here, was that as the VFR is much heavier than the ZZR250 that I have the KR1-S frontend one, then they should be about right, they are around .75-.80Kg/mm compare to the VTR's .58Kg/mm (not sure what the KR1-S rate is as standard but soft to me).

The last modification was to grind the rebound damper taper on the VTR rebound rod, to be a full taper, rather than the limited stepped one they have as standard. You can read about it here http://www.vtr1000.org/phpBB3/viewtopic ... 31&t=29710

So cleaned & bolted it all together then added fork oil & set the air gap at 135mm & added the fork caps. Refitted the forks & front wheels etc & it all looks good. One advantage is the VTR stanchions are 54mm taller than the KR1-S so I can now mount my SV650 bars above the top yoke, which fixes the clearance issues I was having with the clocks & tank :)

I'm fitting a KR1-S swingarm to the ZZR at the mo, so can't report on the ride quality yet, but will do as soon as I have the bike back together.

Enjoy :)
Last edited by Mohawk on Sat Jan 30, 2016 8:07 pm, edited 1 time in total.
Half a KR-1S, well the front anyway :)

dmac
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Re: KR1-S Cartridge Fork Conversion

Post by dmac » Sat Jan 23, 2016 8:17 pm

Good info there,

Looking forward to seeing how it rides.
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Professor
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Re: KR1-S Cartridge Fork Conversion

Post by Professor » Fri Jan 29, 2016 11:29 pm

The KR1S std fork springs start at about 0.6 kg/mm and are progressive or dual rate.

Are the std VTR1000 fork springs straight rate? they might be ok for a light rider on the road, maybe you could measure the outside diameter and length for us, too soft anyway for most people.

The VFR800 std springs are listed as being 0.74 so should suit a heavier(very heavy if for normal road use) rider, maybe 115kg?
Race use might suit about 97kg rider?

h***a RS250 springs might have suited but are no longer available new
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Professor
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Re: KR1-S Cartridge Fork Conversion

Post by Professor » Fri Jan 29, 2016 11:42 pm

Maybe if you ever take the VFR800 springs out it would also be handy to know their size, unless you made a note of their dimension
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Mohawk
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Re: KR1-S Cartridge Fork Conversion

Post by Mohawk » Sat Jan 30, 2016 12:18 pm

Yeah the reason for using the VFR springs is I'm 100Kg with gear & the ZZR250 is a bit heavier than the KR1-S.
It's one of the sweetest steering bikes I've ever ridden.

The VFR springs have a free length of 382mm, minimum service limit is 375mm, they are dual wound progressive, but the second winding is quite tight, so mostly only uses the wider spaced coils.
Half a KR-1S, well the front anyway :)

Mohawk
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Re: KR1-S Cartridge Fork Conversion

Post by Mohawk » Tue Mar 08, 2016 11:57 pm

Well the cartridges are in, the bikes now also has KR1-S swingarm & VTR250 4" rear wheel. It's a Z spoke rather than H spoke like the KR1-S front, but looks identical unless you look closely, a nice matching 5 spoke pair, will take 140 or 150 section tyres to !

Some pics here https://www.dropbox.com/sh/kcg0auipynoc ... 3anya?dl=0

I've only bounce tested it & rode up my street to check all was OK, will sort out MoT next week, then give a ride report. The front feels much taughter now & the change in leverage ratio makes the front and rear feel like a really good match. Only some fast twisties will tell for sure.

Enjoy
Half a KR-1S, well the front anyway :)

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JanBros
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Re: KR1-S Cartridge Fork Conversion

Post by JanBros » Wed Mar 09, 2016 12:41 am

good job.

would like better pictures of the rear wheel, it's dificult to see how it looks now.
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Mohawk
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Re: KR1-S Cartridge Fork Conversion

Post by Mohawk » Wed Mar 09, 2016 4:37 pm

Thanks. Will have to wait till next week, I'm away for a few days.
Half a KR-1S, well the front anyway :)

Mohawk
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Re: KR1-S Cartridge Fork Conversion

Post by Mohawk » Thu Mar 17, 2016 5:24 pm

Had the bike out for a sneaky test run before MoT next Saturday & all i can say is wow, the frontend is fantastic, gone is the too soft feeling it had with full preload. Gone are the jolts through the bars when hitting bigger bumps, its like ridinga magic carpet, just sucks it all up & feels bootiful on the brakes to boot :)

I'd recommend this upgrade to anyone, probably just as good as later/other fork swaps.

The backend all works as intended, just need to sort out the front brakes as they still feel wooden, will try to get the Nissin calipers on before Saturday.
Half a KR-1S, well the front anyway :)

Mohawk
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Re: KR1-S Cartridge Fork Conversion

Post by Mohawk » Tue Apr 05, 2016 6:35 pm

OK wheel pics

https://www.dropbox.com/s/yegphtbas4cwb ... .jpeg?dl=0

https://www.dropbox.com/s/a763eyeceze2y ... .jpeg?dl=0

https://www.dropbox.com/s/6ujlprtfe842i ... .jpeg?dl=0

Enjoy. VTR wheel is Z section where KR1 is H section, but you'd never notice unless you look very closely.
Half a KR-1S, well the front anyway :)

Mohawk
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Re: KR1-S Cartridge Fork Conversion

Post by Mohawk » Tue Dec 27, 2016 9:52 pm

Just to update that the handling is great, bumps are controlled much better than with the damper rods. And of course the cartridges damping can be tuned to own requirements either by using a suspension specialist or RaceTec gold cartridges if you fancy DIY.
Half a KR-1S, well the front anyway :)

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