An Unholy Union III: WP 4860 USD Forks on an Airhead

[bgoodsoil]

I'm getting 134mm.

[One Less Harley]

OK I went outside and looked at my old G/S front end and looked at the steerer tube, for the inner race on the steerer tube spacing is 137mm. The outer race distance would be less. So my original guess is wrong.

[Renner]

136.8mm between outer race seats on an early /5 frame.

sorry for the delay, had to tear it down.

D'oh!
205'd while wrenching

[igormortis]

Just pulled the forks and steering stem.

I get a measurement of 137mm without pulling the races.

Hard to tell for sure without removing the races, since they have a taper, preventing a solid stop to measure against.

Bike is a 1985 R80 Mono.

[igormortis]

Argh. Me too.

Originally Posted by Renner

sorry for the delay, had to tear it down.

D'oh!
205'd while wrenching

[AntonLargiader]

My notes (for an R65 frame I think) say 131mm between bearing seats.

EDIT: full notes:

The BMW head tube is 131mm between bearing seats, putting the inner races of the steering head bearings that same distance apart. The EXC stem allows the inner races of the KTM bearings to be 151mm apart, but the 7mm shorter stem (59401033000) from the smaller bikes should reduce that to 144. Machining the stem from 29mm down to 28mm lets the bearing drop down another 10mm, to 134. A spacer can take care of the rest, although that would raise the front of the bike. Furthermore, if the tubes are raised fully in the lower triple, the upper triple will not go down the extra 7mm, so we'd be gaining 7mm of height.

[Airhead Wrangler]

Hot damn. A lot can happen during the ride home from work. I'll update the drawing tomorrow. None of this changes much, everything still works fine. Woo.

[bgoodsoil]

thanks!

[Airhead Wrangler]

OK, 137mm seems to be the consensus, but Anton's measurement of 131 is a bit troubling - maybe chalk that up to being an R65 frame. 137mm seems to jive well with R-Dubb's design, specifically the length of the steering stem.



This measurement is more in line with what Anton was talking about - the bottom clamp just barely staying within the bottom clamping area. Only 3mm to spare here.

[Airhead Wrangler]

Let's change gears and talk about brakes:

I'm not sure what happened since the last time I bought a brake rotor, but apparently somebody decided that all brake rotors from now on should look like goofy ass ninja throwing stars, something a 17 year old might buy at autozone for his juiced up honda hatchback with a huge muffler.



Anybody know of a good quality regular old ROUND brake rotor for KTM dirt models? Ideally, something larger than OEM KTM and floating.

Does anyone know about compatibility of dirt model, LC4, and LC8 rotors? They look like the same bolt pattern and diameter. They don't seem to have any lateral offset. Anyone tried switching them between bikes?? I plan to use the stock caliper and MC of a 2006 250SX-F.

[jbcaddy]

Originally Posted by Airhead Wrangler

Let's change gears and talk about brakes:

I'm not sure what happened since the last time I bought a brake rotor, but apparently somebody decided that all brake rotors from now on should look like goofy ass ninja throwing stars, Anybody know of a good quality regular old ROUND brake rotor for KTM dirt models? Ideally, something larger than OEM KTM and floating.

Does anyone know about compatibility of dirt model, LC4, and LC8 rotors? They look like the same bolt pattern and diameter. They don't seem to have any lateral offset. Anyone tried switching them between bikes?? I plan to use the stock caliper and MC of a 2006 250SX-F.

those new style rotors are lighter, run cooler and when you play in the dirt, can work longer before getting jambed up with mud. Motostrano has some kits with larger rotors for supermoto that will work for you

http://www.motostrano.com/

[Airhead Wrangler]

Originally Posted by jbcaddy

those new style rotors are lighter,

They're lighter because they're half air. I'm thinking they'll probably last half as long.

[One Less Harley]

are all upside down forks from KTM 250 and up all 4860's?? What about spring rates, caliper mounts and axles? I assume they are different? Would it be better for the front end to come from a 250cc or larger and 2000 and newer? I haven't seen where this has been discussed w/ the 4860's. Just thinking of picking up a set for possible future use.

[Airhead Wrangler]

Originally Posted by One Less Harley

are all upside down forks from KTM 250 and up all 4860's?? What about spring rates, caliper mounts and axles? I assume they are different? Would it be better for the front end to come from a 250cc or larger and 2000 and newer? I haven't seen where this has been discussed w/ the 4860's. Just thinking of picking up a set for possible future use.

What's written below is MY UNDERSTANDING and should not be taken as fact. Do your own research. That said:

They started using 4860s in 2001(?) I believe and not on all models, some got the 4357s. In 2003 they did away with the 4357s and changed the axle size on the 4860s from 20mm to 26mm. In 2007 they switched from what they call a single chamber design to a dual chamber (what the rest of the world calls cartridge forks). I can't remember which models from 2007 on got the closed damping cartridge (only SX models?). As far as I know all the 2003+ 4860s use the same 26mm axle except for the 950/990 adventures which use a 30mm axle. From everything I've read all the 4860s have the same caliper mounting arrangement. Steer clear of the supermoto models as they appear to be unique in a lot of ways and are incompatible with a lot of parts that all the other models share. Also, the 950/990 adventure models have longer uppers and shorter travel than the dirt bike models. The 640 adventure had forks that as far as I can tell are identical to the dirt models with the exception of optional dual discs.

In short, the 125-525 SX, XC, EXC, models 2003-2011 are identical externally (length, travel, caliper mounts, axle). The SX models (I think) from 2007 on have closed cartridge internals.

[igormortis]

Originally Posted by Airhead Wrangler

ninja stars

Have to agree with you there. Have you considered the HE discs?