Fork and swingarm swap: will these brakes stop this crazy thing?

[Spider John]

After staring and an XS650 frame and engine sitting around the shop being neglected, I recently did some horestrading and ended up with it plus a stripped down KX125 with complete front and rear. I'm confident that the forks and swingarm are WAY overbuilt and more than sturdy enough for my application. HOWEVER, I'm not so confident that brakes mean to stop a small bike in the dirt aren't going to explode the first time I try to haul it down from speed. Thoughts? Are aftermarket rotors meant for the KX much of an improvement? Other options? Trying to keep this as low-budget as possible, not that brakes are anything to skimp on.

 

[Spider John]

FWIW, the swap was pretty straightforward. Tapered roller bearings for the KX stem/ XS neck are readily available. Need some swingarm bushings with a slightly smaller i.d. but the width and length are perfect. Clearance for the rear brake pushrod is tight, but I should still be able to mount the KX rear master cylinider inside the frame. Looking at the feasibility of using the monoshock, otherwise I'll add some lower mounts to the swingarm.

 

[Spider John]

Moving forward with the monoshock, we'll see where this goes.

 

[I am Carbon]

I would think the brakes will stop the xs just fine. Probably stop the thing better than the oem brakes will. Just my opinion the front brake looks to be 4 piston can't tell about rear. If you are going to use the kz rear wheel I would make sure that you can get a sprocket that will work for you. some where in the 30 to 34 tooth range

 

[Spider John]

Hey, thanks for the response. On lookout for the right sprocket. Converting to 520 and upping the front to 18 since the smallest rear I've found so far is 36. That'll at least get me up to stock, though I'd prefer higher.

 

[I am Carbon]

if you can't find one go to rebel gears they can make you one
I had a weird rear wheel on my bike when I bought her and the smallest sprocket I could find was 38 rebel gears made me one with 32 tooth If memory serves it was around $65
I see they can make you one down to 30 tooth

https://www.google.com/url?sa=t&rct...=PowxLehNT0Mmg4N06XE06Q&bvm=bv.80642063,d.eXY
this link is for catalog http://www.rebelgears.com/images/34397_RebelGears_2012_Catalog.pdf

 

[Spider John]

Haven't had much time to work on it but progressing slowly. Running 18/36. Got the lower monoshock mount located and everything bolted up so I can locate the top mount. Smaller rear sprocket is limiting range of articulation with the fat swingarm. Not sure how much initial sag I'll have but the plan is to have the chain just barely touch the top of the swingarm while unladen, then lift off once loaded in order to maximize the usable range before the bottom hits.

 

[fredintoon]

Hi Spider,
FWIW except for being 1/8" narrower 520 chain is the same size as 530 chain so 18T puts the chain perilously near the shifter shaft either way and I got the gnaw marks in my shifter shaft to prove it.
I've seen dirt bikes with nylon rubbing blocks to keep the chain off their swingarms, perhaps you could look at doing that for your conversion?

 

[gggGary]

 

[Spider John]

Only one I have on my phone at the moment.

 

[Spider John]

Ok, found this one too, shows the grafted lower mount from the Kaw.

 

[gggGary]

 

[Higgo62]

Is the swing arm the same length as the original yam one? I like the look of it and would like it for a project xs I'm working on, but would like one a bit longer than stock.

 

[Spider John]

It's about 3 inches over stock.

 

[ZAIN DIAZ]

Bien jajaja casi lo mismo que hice yo,
bien hecho

 

[Spider John]

Yes, the 18T front is indeed frighteningly close to the shifter and the clutch rod. Time will tell I suppose.

 

[db1337]

Hey there, those brakes have enought power. The problem is the rotors are very thin and don't handle braking needed on streets. They're made for hard braking for a very short time on a MX track. With the heavier bike and frequent braking from higher speeds, you'll quickly see the issue. That's why everyone changes rotors on supermoto bikes. The stock rotors get glowing hot and warp very quickly, even at casual supermoto speeds. I thought I could skimp on my supermoto bike, but on the 1st lap on a VERY small kart track the front rotor was toast.

 

[Spider John]

Ah, my concern exactly. It looks like some of the aftermarket rotors may be heavier. Most are just petal or other designs which may actually be even thinner.

 

[Spider John]

Floating or solid? Oversize or just heavier?

 

[chizler62]

Doubtful those brakes will like you. You will not like them too much either. But, you'll get by.
OMG....the rear fender looks like a tampon string hanging off the back...shorten that grab handle etc...lol
Kidding aside.....you did change the motion ratio of the rear linkage a ton between changing the wheelbase, rake,trail,weight,etc and especially the top shock mount by laying the shock down more. This will change the anti-squat making setting sag difficult but not undoable. Which with the added weight of the motor may be good. Also take an account the Head Tube angle change and from 70 to ?
Does the nose dive heavy when slowing down?
Does the steering seem "lazy" at slow speeds?