YZ USD Forks on a KDX

Questions and comments about converting to beefier forks..
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Jeb
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YZ USD Forks on a KDX

Post by Jeb »

I've nearly what I need for the YZ forks install on my 220 - they're gonna work fine!! 'Hope to get things put on next weekend - waiting on fork guards and 7/8" bar mounts to arrive:

'98 YZ125 USD Forks: KYB 46mm forks, no "bladder". Bottom clamp stem hole matches KDX bottom clamp stem hole. Stems are very close to being the same length so additional spacers will be minimal or not needed. There's about 0.075" gap between KDX stem and YZ upper clamp hole that will be resolved with shimming. MX-Tech rebuilt my inner cartridges. I removed 6 24mm shims out of each base valve to bring the total to 4-24mm, 1-22mm, 1-20mm, 1-18mm, 1-16mm, 1-12mm (all 0.5mm thick, 8mm ID). I replaced the seals/wipers/bushings. Everything cleaned/flushed and put back together. I've got 5wt fork oil with 100mm level to start with. Currently I have the stock springs - 0.41 kg/mm.

'96 YZ250 wheel: Nice wheel purchased off of ebay with a gold Talon hub. Bearings feel good.

'02 YZ250F axle: Fits great. I'll need to make up a small spacer but axle fits the forks and the wheel.

I assembled the forks/axle/wheel and tried on the KDX caliper - fits great!

I'll need to fab a steering stop much like what others have done, pretty straightforward.

I'll have to be creative on mounting the fender as the holes don't line up, but I've got some ideas . . .

I'll be doing some stem swapping this Friday - we've got a press at work so that comes free!!

I'll have pictures / methods / costs on the site in time
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Post by 2001kdx »

Good report. It's good to know the yz forks will work well. Makes ebay life easier.
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Jeb
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Post by Jeb »

'Got things finished up today. Overall, things worked out pretty good:

Took 5 tons to press out YZ stem, 10 tons to press out KDX stem. Steering stem required slight knurling to press-fit nicely in the bottom clamp. Wish I couldv'e gotten a picture of the knurling - the shop did a really nice job.

Ended up putting in a couple of flat spacers in. If I need to raise the tubes in the clamps a little more I have room for some more spacers if needed. I used three pieces of 0.025 shim stock to fill in the gap between the stem and the top triple clamp hole.
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Right now the tubes are "raised" about a half inch. Found some aftermarket bar clamps for standard-sized bars - not bad!
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Used a reasonable facsimile of the steering stop others have used - works fine!
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Lightspeed makes some great USD fork guards for the older YZ forks. Rather than route the front brake cable down the front of the guard and around the bottom of the fork, clamping is provided much like the '05 YZ forks. The '96 wheel came with one of those Talon hubs. Need some new tread in the front, though.
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I used all of the triple clamp KDX hardware used to mount the front brake guides as well as the headlight. I added a piece of relatively thin aluminum angle (Home Depot, used for screen doors/windows) to mount the bottom of the headlight to the YZ bottom clamps (still a little rough, I need to clean it up a bit). I was able to use the KDX hardware to mount the top of the headlight because the top clamp was aftermarket (the pinch bolts on the stock top clamp are oriented on the side of the clamp so this is not possible in that case)
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KDX caliper works with the YZ fork / wheel. I did have to add a couple of washers to the bottom mounting bolt because it's too long - I'll replace it with a shorter bolt in time.
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I gave it a little test ride in the woods after the pics, can't wait to really put it to the test. I likes!! 'Seems a little harsher than the KDX forks on the small bumpy stuff but I haven't dialed anything in yet. However, it swallows logs, feels cushier on landings, and turns sharper & more accurately despite a worn tire.

Worth mentioning: I noticed a distinct feel (i.e. great hookup) with a brand new Pirelli MT16 (110/100) and RB power despite loamy woods conditions - cool!!

Bottom line: this era of YZ forks work just fine in the KDX!!
"No farmer ever plowed a field by turning it over in his mind" -George E. Woodbury

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Post by FRYSPEED »

Its great to see Talon hubs on a KDX.I live 6 miles from the factory so picking up my sprockets is easy!I have fitted KXF250 forks on the front of my 90 kdx and fitted the kdx front wheel.But a Talon hubbed KXF front wheel would be so sweet!!! :supz:
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Post by Indawoods »

A1 conversion Jeb! :supz:
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Post by IdahoCharley »

Nice conversion and write-up.

FWIW - If you need to soften up the forks and are not using within 25mm of full travel try removing some oil from the forks first. 100 mm air gap is pretty tight and I believe ~ 120-130 level is more common for woods riding.
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Post by kawagumby »

Just something to think about...

I'm using a 99 yz triple with my kx forks and it looks identical to yours. You might want to keep tabs on how the front end works in slick stuff, I've found that the handlebar location is a bit too far back to make a quick easy rider transition to load the front end (it is further back than the kdx location). At a ride last weekend in mud and frozen ground I had several major unpredictable washouts...coincidentally, a fellow rider had a 2001 YZ and the triple had the handlebar location a good 3/4 inch further forward. Sooo, I'm planning on getting a later version to move my bars further forward.
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Post by Jeb »

Thanks for the suggestions, guys - great stuff!!

IC: I bet I'll end up removing some of the oil as you've suggested, 'might try it tomorrow before I go riding. I will end up on the track with my youngster from time-to-time so, on the other hand, the bottoming resistance from the higher oil level might be a good thing. If I understand subtanks correctly, that might be a good "have your cake and eat it too" scenario. With oil level something like what it is now, I could close the needle valves when on the track, open them when I'm in the woods. Given how pricey the subtanks are, though, I might try to fab the subtanks out of PVC like one our members did. May not need it, though - I don't exactly air it out an awful lot on the mx track, so removing some oil may be all that's needed!

Kawagumby: One option I have with the aftermarket bar clamps I bought is the offset. Right now I have the offset pointed back, so if I experience the same problem I could try to rotate 'em and see if that helps. I'm guessing it's a 1/2" to 3/4" difference. I did notice some slight understeering a few times - not bad though - and was wondering if it meant I needed to raise the forks in the clamps a tad more. Or maybe it was me!! Thanks for the heads up, another thing to consider as I dial things in.

This afternoon, my son and I took our "new" bikes out on a farm we ride in sometimes. Perfect place for both of us to get use to the changes - him a genuine racer (RM65), me the RB mod & forks. A lot of wide-open, smooth sailing as well as some rough terrain/jumps behind a dried up pond, and a small stretch of woods (pretty flat but the slow-moving, gnarly stuff all over it) . . .

I have an entirely different bike!

*The first time I went airborn off of one of those jumps I was bracing for the bike's reaction and . . . almost nothing! Those forks sucked up the blow - talk about bringin' a smile to my face.
*I started hitting some of the stuff there and in the woods and these forks absolutely swallow that stuff. MAJOR improvement.
*Maybe I was just elated to be riding the bike after working on it like I have, or maybe the turning just improved like 10-fold. I was worried that between a slightly elevated rear end (the new Pirelli did that) and the slightly elevated front end from the forks that the center of gravity would worsen handling (I'm 3/4 higher now) - boy was I wrong. I turn faster and more accurately.
*It is a tad rougher in the bumpy stuff at slow speed, though - I'll probably give removing a little of the fork oil a try.

And, ooohhh geez how could I forget to mention - the power on the bike is absofreakinlutely awesome
*The powerband is strong but comes on so controllably.
*I get great pull throughout the RPMs. I also get a sweet hit - it starts before the KIPs and extends right through it!
*It's like having a mild-mannered 250. I can be seated in the cradle, no clutch, and very controllably lift the wheel in the first three gears just about whenever I want to and how I want to - that is an awesome thing. I had the front wheel come off the ground in 4th a couple of times :shock: (but not in a vicious manner). And there's more at the second sweet spot!??? I might go looking for it tomorrow (yes, we ride again . . .).
*Terrific "launch" power - when you really want to go it's there with some clutch. From a near standstill after a tight turn I could snap it into second, give it a bunch of throttle with a nice jab of the clutch could be in KIPSville quickly. Do it again really quick w/ third, more KIPSville - yeah, there's DEFINATELY more power in those mods . . .

Not a smidgen of a regret for the money & time spent on these mods - so very much worth it.

The youngin' had a day, too. Man, when he got on the pipe he was cookin' - that little yella' thing would move. I spent some time behind him and when he opened it up he would pull away from me and be kickin' up a dandy rooster tail! He's handling things quite well out on the open. He started to get brave behind the pond until he hit the powerband just right coming off the face of one of those jumps :shock: . He didn't lose it, but it woke 'em up a bit! Won't be long, though, and he'll start mastering it, I'm awfully proud of him!
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Post by canyncarvr »

This is real old-hat stuff...but don't overlook the simple stuff. Maybe it's only me that does that...but I decide to ride a setup for awhile to see how it works here, there and other places...then don't get around to fine tuning it.

I'm very guilty of that with clickers..I set them..they seem fine (or I'm just used to them), then it 'occurs' to me that I haven't really done any bracketing for test purposes...and I find a whole new being lurking a few clicks away.

I've done that more'n once......... :oops: ..and yet again just last weekend.

Repeat for emphasis..or simply agreement..buy I'll bet you will like 110-115mm a whole lot better than 100mm. DO put that on your list of 'Things To Do'.

Thanks for the info!!

Happy Riding!

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Post by dirtykdx »

Okay, you sold me on the idea.

I started asking around for any late 90s or newer MX forks. Well, 3 days later I get someone that makes me an offer. $85 + shipping for a set of 99 YZ 250 forks and triples. Combine that with an *bay wheel and axle, and I should be pretty much ready to rock on it.
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Post by Jeb »

Dirtykdx - your "deal" doesn't sound bad at all. If you look on *bay right now there's several rigs available, with or without the clamps (which are also very available), including this '98 set:

http://cgi.ebay.com/ebaymotors/98-YAMAH ... 2922QQrdZ1

The newer ones obviously are going for more.


____________

Many thanks for the suggestions from IC, kawagumby, & CC. At this point I'm at a 110mm level, rebound clickers are 8 clicks from "slowest" setting and the compression clickers are 3 clicks from the "softest" setting - things indeed are easier on the old shoulder sockets (and I've still got plenty bottoming resistance). Ride is considerably plusher. Weather permitting, I'm going to start over bracketing rebound then get the compression clickers dialed in again. I need to fiddle with the AS on the carb as well as I found-lost-found-lost the SSS (but that's for another forum!)
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