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Another USD fork Conversion Complete w/ pic

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Just got my bike all back together and the the snow has melted. Can't wait for the mountain roads to finish melting so I can get out and really sort the front end!

 

Thanks goes out to Ron @ RSW racing for hooking me up with his sweet lower clamp that lets you use the stock XR stem to do the conversion.  Ron is a great guy, if you guys are looking to do the conversion don't hesitate to call and talk to him.

 

The forks are off a 2004 CRF250R. I bought the entire bike locally for $500, motor was complete smashed to pieces, looked like a stick of dynamite went off in there. Sold what was still good on Ebay, actually made money on the fork upgrade.

 

I totally rebuilt them all new bushings and seals, and did my first attempt at a revalve.  Spoke to quite a few folks and did a lot of reading before I started the revalve.  I haven't touched the mid valve yet because I want to see how it feels with the changes I have made. I was able to get out and hit a few rock gardens, the forks just soak it up. I think I am close to something that works well on this old Pig.

 

If you have any questions shoot me a PM I will be glad to try and help out.

 

 

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Looks good.  These 47mm showas are good for learning because there is so much info available online.  One recommendation is to be festidious about cleaning all the grinding grit from inside the base valve stem where you had to grind off the peen.

 

What base valve stack did you try?  I'm running .47 rate springs from a 450R; I think the 250R forks have .45 rate. I'm currently:

 

Base valve

30.1 (x12)

21.1 crossover

28.1

26.1

24.1

22.1

20.1

18.1

16.1

14.2(x2)

 

Midvalve

20.1(x3

17.1(x4)

float - .25mm

Edited by heart_of_darkness

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Something to be cautious of is fork overall length.  These USD forks are longer than the stockers, so have to be installed very high in the triple clamps to maintain normal steering geometry.  The concern is that when bottomed the tire may hit the underside of the fender before the forks bottom internally.  One way to test is to reassemble the forks without the springs, then install everything back on the bike.  Without springs, it's easy to cycle the front wheel through its travel to check for fender contact.  It's also a good time to check the position of the axle relative to the right fork's boss to eliminate fork binding.  If the hollow hex end of the axle is even the tiniest bit mushroomed you must grind off the high spots so that the axle will slide through the right fork leg lug.

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Nice,,Semi finished mine as well. I'm going to pull them again shortly and sort a few things out,,Think I have too

much oil in them,,kinda stiff. One of the legs is also a bit spongy compared to the other,,not sure whether it's the repaired damper rod one

or the other normal fork, Need to strip them down for a look. Not difficult to use the 600 stem,,Shim top and bottom and

press it in..Nothing more needs doing unless you are trying to use the stock 600 wheel and speedo drive..An axle needs modding

for that..Cost me 150 for the completed job,,axle included and I came away from my engineer/brainbox with another 600 frame and disc

brake swingarm,,Can't complain at that deal..

Edited by Horri

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Slight update with mine, Stripped them down today and replaced the oil in both chambers,,this time correctly. Difficult finding

an explanation of doing both chambers on the net. Severe lack of info though I did find one explanation and managed to figure

the procedure out. The CRF450 manual is totally useless for the operation.,forget that sucker entirely..All very well explaining how

you do the seals all over the net (that parts easy) but useless if you don't explain the bleeding off of air from the inner chamber and

the filling of oil into the different chambers correctly or well enough..Problem I have now is I think I smashed my used bottom stem

bearing a bit much getting it on when I first installed it to the stem..Bearing appears gone so I'm going to try and tighten the top up

a bit more tomorrow. If that fails to take out the wobble/flex that's there now I'll have to get a new bearing to fix it..Off the entire shebang

will come again..Joy joy..

Edited by Horri

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Slight update with mine, Stripped them down today and replaced the oil in both chambers,,this time correctly. Difficult finding

an explanation of doing both chambers on the net. Severe lack of info though I did find one explanation and managed to figure

the procedure out. The CRF450 manual is totally useless for the operation.,forget that sucker entirely..All very well explaining how

you do the seals all over the net (that parts easy) but useless if you don't explain the bleeding off of air from the inner chamber and

the filling of oil into the different chambers correctly or well enough..Problem I have now is I think I smashed my used bottom stem

bearing a bit much getting it on when I first installed it to the stem..Bearing appears gone so I'm going to try and tighten the top up

a bit more tomorrow. If that fails to take out the wobble/flex that's there now I'll have to get a new bearing to fix it..Off the entire shebang

will come again..Joy joy..

 

There's an easy way to test if the inner cartridge is correctly filled and bled.  With the cartridge assembled (base valve screwed in), compress the damper rod completely and then let it extend back out on its own.  The rod should extend smoothly and all the way out.  If it doesn't, there's still some air trapped inside.

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How far up over the top clamps are you setting the fork legs? 

I've only done one test ride with mine but I have them set at the second line down from the top of the forks,,20mm or

so protruding through the top tree,,Seemed to track fine to me at that..bit higher through the top tree may be slightly

more responsive for tight riding.

Edited by Horri

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There's an easy way to test if the inner cartridge is correctly filled and bled.  With the cartridge assembled (base valve screwed in), compress the damper rod completely and then let it extend back out on its own.  The rod should extend smoothly and all the way out.  If it doesn't, there's still some air trapped inside.

Yep..done all that,,Seems ok now..Ordered a new bearing,,picking it up later today. The stem was kinda loose after my

test ride the other day (possibly just a bedding in issue) so I tightened the nut below the top tree a bit and it seems to

have removed the wobble/flex signs of a bad bearing..Test ride will tell me whether it's good for a bit or whether I'm going

to have to pull the trees and stick the new bearing in..I'll at least have the new bearing so if the issue persists off they'll come..

Edited by Horri

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How far up over the top clamps are you setting the fork legs?

Hold the new and old fork side by side, aligned at the axle hole. The extra length of the USD fork is how much should stick above the triple. USD forks of different years are different lengths, so there's not a set answer.

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Thanks, I have 2007 crf450 forks with one line at the top. Had it set there, about 5 mm I would say. 
Moved them up another 12mm, so about  17mm in total. First test ride today...

I also need to mount my new rear shock, my current is pretty much worn out and has a massive amount of sag...


Update 
Measured for top of cap nut to top of clamp = 25mm. Drove to work and felt really good. Will probalbly go down to 20mm when I get the new shock mounted. 

Edited by no66

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The 2005-2007 forks are 6mm or 7mm shorter than the earlier forks.  Then the 2008 forks are another few millimeters shorter yet.  The later year shorter forks are slightly preferable for not needing to stick up above the triples as much. 

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Due to a lack of knowledge on the net,  I feel a documented write up  coming up in your future  ;-)

Slight update with mine, Stripped them down today and replaced the oil in both chambers,,this time correctly. Difficult finding

an explanation of doing both chambers on the net. Severe lack of info though I did find one explanation and managed to figure

the procedure out. The CRF450 manual is totally useless for the operation.,forget that sucker entirely..All very well explaining how

you do the seals all over the net (that parts easy) but useless if you don't explain the bleeding off of air from the inner chamber and

the filling of oil into the different chambers correctly or well enough..Problem I have now is I think I smashed my used bottom stem

bearing a bit much getting it on when I first installed it to the stem..Bearing appears gone so I'm going to try and tighten the top up

a bit more tomorrow. If that fails to take out the wobble/flex that's there now I'll have to get a new bearing to fix it..Off the entire shebang

will come again..Joy joy..

 

 

 

 

 

 

 

 

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Hmmm..Yes..Could be a slight problem with my attempting a write up as I'm not totally sure on whether the inner 

chamber with the damper rod is ok to be upended before you put it back into the outer chamber. I'll have to ask my

engineer friend a few more questions on that part as I didn't upend the forks at all when refitting the center. Made the job

a bit more complicated than I think it should be..Had the fork legs hanging from a tree at one stage to avoid my upside down

confusion with the central damper rod section. (No garage nor vice so the tree had to do the job),,Truth be known.. I still don't totally understand the

double chamber oil change system that clearly..I managed it best I could with my limited info..They are certainly a strange

sort of system the twin chambers but once I have it totally down pat you can expect the usual.. :blah:  if anyone needs to know how it's done. :)

Most important part is the pumping of that damper rod to clear any possible air from its workings..Rest,,straightforward info from what's out

on the net already regards changing the seals..

Edited by Horri

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Hi Guys, a noob here.

I just picked up an '88 NX650 Dominator. I would like to swap out the OE front end and have found a few references to CR500 front ends. Can anyone point me to a previous post with info regarding a swap on my model of bike?

If not, does anyone know if the NX650 shares frames/parts with other models like XR650 or similar that I can follow someone's previous build.

 

Oh, I'm also looking to change the rear shock for something a little more capable.

 

Thanks!

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Once the inner cartridge is bled and assembled, the last step is to fully compress the damper rod (screw the long nut thing onto the bottom threads to provide a stop at full compression.)  That will purge any excess oil past the base valve.  You then need to upend the assembly to pour that purged oil out of the drain holes at the top of the cartridge body.  Once all of that is done, there's no problem inverted the assembly or even twirling it like a batton.  It is standard practice to invert the fork when attaching the base bolt at the very bottom.

 

There are several youtube tutorials for these (or equivalent KYB) forks.  RockyMountain has a decent video.

Edited by heart_of_darkness

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Hi Guys, a noob here.

I just picked up an '88 NX650 Dominator. I would like to swap out the OE front end and have found a few references to CR500 front ends. Can anyone point me to a previous post with info regarding a swap on my model of bike?

If not, does anyone know if the NX650 shares frames/parts with other models like XR650 or similar that I can follow someone's previous build.

 

Oh, I'm also looking to change the rear shock for something a little more capable.

 

Thanks!

 

If the NX has the stem steering stem/ bearing arrangement as the other XRs, the only CR500 forks that are bolt on are from a 1989 model (I think).  I think the CR250 forks from that year are the same. 

 

Any other year requires conversion bearings or conversion steering stem or conversion triple clamps.

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Once the inner cartridge is bled and assembled, the last step is to fully compress the damper rod (screw the long nut thing onto the bottom threads to provide a stop at full compression.)  That will purge any excess oil past the base valve.  You then need to upend the assembly to pour that purged oil out of the drain holes at the top of the cartridge body.  Once all of that is done, there's no problem inverted the assembly or even twirling it like a batton.  It is standard practice to invert the fork when attaching the base bolt at the very bottom.

 

There are several youtube tutorials for these (or equivalent KYB) forks.  RockyMountain has a decent video.

OK..Sounds like I may still be doing it wrong..With the damper rod section removed from the center and oil drained off I filled the damper section

with the required amount of oil for it then purged the system by pumping the rod. Once that was done in went the top end clicker part and into the

outer chamber that lot went and all the nut/bolt crud and clicker was installed to the bottom of the damper rod/outer fork leg section..All this without upending

the damper section at all..Then I filled the outer chamber with it's required oil and buttoned up the top end of the fork..Any issue you see there..???

 

Part I don't quite get is that the inner damper section has holes in the sides of the chamber that I guess allow oil or something to flow between the two chambers.

If you up end that central section when putting it into the outer surely all the oil you've put into the center will flow out the holes and consequently

out of the center damper section....I'm confused on this??/,,Does having the top clicker short valve type thing in somehow prevent the oil coming out those holes..??

If not I just don't get the point of filling the damper section only to have the oil you just put in all come out those holes and go into the outer chamber

or out onto the ground as the top monster nut is not secured to the outer chamber at that point..Makes little sense to me that..

Edited by Horri

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Check out the CRF450R forum, spifically the DIY fork rebuild thread. There are some good diagrams there.

 

The top clicker thingy is the "base valve." It has some O rings that seal the inner cartridge oil inside.  Those vent holes on the top are for purging out any excess oil or air that was left after serviicing.  I don't think there's any mixing of the inner and outer oil during normal operation.  Othewise, as you noticed, there'd be no point to the twin chamber design.

 

You're right that it's possible to reassemble the fork without inverting it.  But, because the cartridge oil doesn't folow out, there's no reason not to do so.

 

PS I'm a fan of shade tree mechanicing, especially if the tree is actually used.  But remember that it's important with suspension to keep the internals spotlessly clean.  Even a tiny grain of grit will trash the seals and bushings and grind through the anodizing.

Edited by heart_of_darkness

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