Project Growth Spurt: building a KX100 for a small adult

[sixstringsteve]

Many won't understand the point of this build, but that's ok. I've tried many different bikes in search for the perfect trail bike for the stuff I like to ride, and I haven't found the perfect bike yet. So I decided it's time to build the perfect bike. I enjoy projects and I enjoy fabricating.

I wanted something light for the technical steep, rocky goat trails I like to ride here in Utah. I have a trials bike, but it makes the trails TOO easy. I'm a shorty, (5'6", 28" inseam, 165 lbs) and I only ride trails and trials (no MX, no desert). So i don't need more than 10" of travel, but something like a CRF230 is too heavy, bulky, and low performance. So I've decided on a KX100.


Pros:
- plenty of power (~25 rwhp)
- great seat height
- super narrow seat/tank (makes it easier to touch the ground)
- super light (150 lbs w/o gas)
- fantastic suspension and brakes
- very cheap
- 2t zip: fun to ride
- plenty of aftermarket. These bikes haven't changed in the past 12 years, and they share many parts with the kx80/85s as well.


Cons
- wheelbase is too short (50.8" wheelbse)
- rider area too cramped
- wheels are too small
- fork angle is a little too slack



Plans for this project

- keep it light. I'd like to stay as close to the stock 150 lbs as possible, but I'm thinking 175 lbs is more realistic.
- 18" rear wheel with a trials tire (maybe even a tubeless trials wheel)
- 21" front wheel (possibly with a trials tire)
- wheelbase stretch: 2" on the swingarm
- 2" frame stretch (behind the head-tube)
- flywheel weight (still undecided)
- low gearing
- steepen the head tube angle a degree or two (still undecided)
- larger tank
- add a light
- lower the foot pegs
- bigger bars
- possibly make it street legal (still undecided if I want to do this)


Anyway, feel free to follow along as I tackle this project. I'll have a lot of questions, feel free to chime in with ideas/suggestions, I'm all ears.

Here's what I'm starting with: a clean low-mile 2000 KX100.

 

[sixstringsteve]

I rode the kx100 today and had a blast on it. I'm learning the powerband on it, and it really has PLENTY of power. It's tough to stop mid-hill and get rolling again, but it is possible. The cockpit was cramped, but more than anything, the wheelbase was too short. So I'll definitely be stretching it, and I can't wait to go up to 21/18 wheels.

A few pics from the ride last night:

 

[sixstringsteve]

I placed an order with Steahly today and ordered the following parts:

- lighting coil
- voltage regulator
- Hi, low, off, kill, switch
- 8 oz fww

Based on my weight (165) and my riding skill (or lack thereof), he recommended an 8oz flywheel weight. Any more and it'd lug too much with my heavy butt on it. He said that if I were a better rider, I'd probably prefer not to have a fww. So until I become a better rider and learn to slip the clutch better, I'm going to fun the 8 oz fww.

Steahly had some great advice for making my kx100 more trail-friendly. He recently built one up for his daughter, and he said the two biggest advantages for her came from decking the cylinder .001 and adding a 10oz fww. Based on his suggestion, I'd like to get the cylinder decked at some point for an increase in low-end.

 

[sixstringsteve]

First order of business is to put an 18" wheel on the rear. There are a few issues here.

1) an 18" wheel won't fit in the swingarm; it needs to be extended at least an inch
2) if the swingarm is lengthened, the brake line will be too short
3) I haven't checked yet, but I don't believe the kx100 swingarm is wide enough for a 4" trials tire
4 the rear hub is a 28 spoke. I can't find any 28 hole 18" rims.
5) if I have to use another wheel, it's going to be too wide to fit in the kx100 swingarm


I think the solution is to find an aluminum swingarm, rear disc, and 18" rear wheel from another bike and graft it into this one. The key will be to keep the weight down. I could easily see this adding 10-15 lbs if I pick the wrong swingarm or wheel.

 

[SportSawyer]

Just save up some money and buy a new Ossa Explorer:

NEW OSSA EXPLORER
http://www.trialmag.net/trialmag/article/5749/NEW+OSSA+EXPLORER

The 2012 OSSA Explorer
http://www.lewisportusa.com/ossa_explorer.htm

EXPLORERS TO BE ARRIVING (in US) BY EARLY JUNE
http://www.ossaworld.com/LearningResources.aspx

 

[sixstringsteve]

those are very cool, I've had my eye on them. Even I could afford the $7200 price tag, I don't think I could ever justify spending that much on a motorcycle.

I also love the idea of the KTM freeride 350, that bike would be a blast for the type of stuff I like.



I figure I'll be into this bike less than $2000 in the end, and it'll still be pretty light. Plus I need another project to work on, and building another rockcrawler is just too expensive

 

[sixstringsteve]

I just ordered a Polisport H4 headlight from Caleb @ Anarchy Motorsports. I ran this headlight on my last hybrid and I absolutely love it. The only minor complaint I have is that it pointed down a bit too much, but that's easily adjusted.

 

[sixstringsteve]

Did a little more research today. I called buchannan's, and though they don't sell a 28-hole rim, they do sell an 18" non-dimpled rim. For $1.19 they can drill the rims to match my hub. So that's about $35 per wheel just for the drilling, plus the $240 for the empty hoop. Plus the cost of spokes and putting it all together. So that's out of the question.

That means I NEED to find an 18" wheel/brake/swingarm from another bike (unless I can find a rear wheel that has the same brake mounting as my kx100).

The good news is that the kx100 swingarm is plenty wide and should fit an 18" trials tire no problem.

 

[Cascadia]

I just ordered a Polisport H4 headlight from Caleb @ Anarchy Motorsports. I ran this headlight on my last hybrid and I absolutely love it. The only minor complaint I have is that it pointed down a bit too much, but that's easily adjusted.

I'm thinking about getting one of these. Is anything else needed to hook it up other than the stock plug? My bright also isn't working and I don't know why. I wonder if it would work on the new light.

 

[sixstringsteve]

I got some parts from Steahley Offroad last week.

- lighting coil
- voltage regulator
- Hi, low, off, kill, switch
- 8 oz fww


First off, I had to pull the flywheel.

 

[sixstringsteve]

The KX100 already has the mounts for the lighting coil, which is nice. Unfortunately the coil didn't come with the screws to attach it, so I had to get my own. For those who care, they're a M4-.70 x 25.

Next up was the installation of the FWW.

It was very straightforward and easy to do.

 

[rholbrook]

What? Thats it? Did you fire it up and try the extra weight out? Come on Steve, I know its mothers day and you just got back.

 

[sixstringsteve]

It's still in pieces.

I've got to get the headlight installed, then I'll take it for a quick spin around the block tonight. With AF Canyon half open, I plan on riding this Thursday, but I'm going to be on the trials bike rather than this.

 

[Rot Box]

Hey thats pretty cool! I like how the lighting coil is its own separate piece.

 

[sixstringsteve]

Anyone have any bright ideas of how to feed the yellow wire through the plastic hose that houses the other wires? I'm thinking of cutting a little slice every 5" or so, but that's a pain and lets dust/water in.

 

[thefirstzukman]

Just sleeve the whole thing with heat shrink. Go to mcmastercar and find some heat shrink with a high shrink ratio that is close to the sleeve that is there now.

 

[rholbrook]

Can you fish some baling wire or a hanger down through there then pull it back through?

 

[sixstringsteve]

I just placed a hefty order with Caleb today:

- IMS 2.4 Gal Tank
- new shrouds
- Skid Plate
- Radiator Braces
- 2 rear trials tires (one for my trials bike)

 

[Chevycrew]

Use one of the existing wires to pull through a piece of twine, then use the twine to pull the original wire plus the new wire back through.

 

[sixstringsteve]

Time for an update. My Anarchy order arrived the day after I placed it:

- IMS tank
- 18" Michelin tube type rear trials tire (plus a tubeless one for my trials bike) - this is for the future when I swap to bigger wheels
- skid plate
- radiator guard
- new shrouds since the pre-2001 bikes only came with one radiator shroud

I got most of those those installed, along with my polisport headlight:

Headlight still isn't wired.