Swapping to XR 400 fork springs

[Darryl K]

I have had a set of stock XR 400 springs sitting in my garage for a year now and finally have the time to swap out my stock '96 KDX springs with the heavier XR units. I seem to remember reading something about making spacers out of schedule 40 PVC but a forum search has produced no info on the subject.

Anyone have any info at all on making the swap to the XR springs?
Thanks,
Darryl

 

[wibby]

No info eh? Here's a couple I found:

http://dirtrider.net/forums3/search...d=305546&sortby=lastpost&sortorder=descending

http://dirtrider.net/forums3/showthread.php?s=&threadid=46249&highlight=xr400+springs

 

[canyncarvr]

If the question is, 'Can you use PVC pipe to make a fork spring preload spacer?' the answer is, 'Yes.'

You don't need a whole lot (of preload). 3-5mm will do. ..assuming the spring is the correct rate in the first place (for your bod).

From an earlier post:

From CDave (3-3-03):

It’s the 1996-99 0.38kg/mm XR400 springs that are interchangeable and commonly used in 1995 to 2003 KDX200/220s.

From racetech:
'96-99 xr400r 43mm showa .38
'00-02 xr400r 43mm showa .40


'H' model kawi spec:
'00 200 kdx 43mm kyb .35

So..they'll fit for you if you're around 160-180# or so (gear added). Depends on your riding style and stuff.......;)

 

[Darryl K]

Thanks for the input guys.

Truthfully, I do not remember what year XR these springs are from. I bought them from a guy in a 4 stroke forum for $25-shipping included. But the reality of it all is that I weigh 210lbs in street clothes so it is unlikely that even if the springs are .40's they will be ideal. The other side of the coin is that I am riding a '96 with stock springs and has likely never had the fork oil changed either. I figure this swap will kill two birds with one stone and while maybe not ideal, will HAVE to be a noticable improvement!

 

[Braahp]

They WILL be ideal.

 

[John Harris]

The Honda springs are not only stronger but longer than the KDX stock ones. Thus you need to cut your PVC for the proper preload you choose. Be sure the two spacers are the same length. I think you may want about 10mm or 1cm of preload. This translates into a spacer of about 1.5 inches if I remember. To say it another way the Honda springs are longer than the stock springs--hense the stock spacer is too long. You can choose to cut down the stock metal spacer rather than use pvc if you choose.

 

[canyncarvr]

-10 from the math department! :debil:

There be 25.4 mms/2.54 cms in an inch, so 10mm be around 7/16s inch. ;)

To each his own....I'm not arguing someone else's choice..but, I found 3-5mm to be a great big fat improvement over 10mm on my bike with the .40 XR springs.

....but then, my street clothes don't weigh so much, neither! (I'm 175-180#)

 

[Darryl K]

Thanks to all, especially Matt for the spring/oil change info on his website. I got the new springs in and used a 10mm spacer. I also changed the oil( 550 ml of 7.5 weight). It was a surprisingly easy task! I even put new Pivot Works seals and bearings in the front hub while I had everything off.

I took a little spin around the neighborhood and noticed a huge difference immediately. It stays up in the stroke better,with much better bottoming resistance. My neighbors Rotweiler even felt more like a hitting chihuahua, I used to bottom hard on him before. :-)

 

[John Harris]

CC you and I are confusing fellow readers. We are talking about 2-3mm of preload and 10 mm of preload vs whatever that might work out to as the total length of the spacer with the XR 400 springs. As I recall even if I used only 3mm of preload that the length of the spacer would be over 1" long. I agree with your math that 10 mm approx equals 7/16 inch and always has. Spacer length is determined to be the distance from the top of the spring with the washer installed to the bottom of the screwed down fork tube top plus the amount of the preload.

We agree that spacer length often is as individual as jetting. Whatever works for you and your KDX.

Cheers

 

[KnoxKDX]

I really loaded mine up when I changed them out...I took a pipe cutter and only cut about an inch and a half off the stock spacers. But I weigh about 210 dressed out.

 

[ChuckyBoy]

Darryl K - I'm laughing my a$$ off!

I'm curious, have you found that S12's or 756's hook up best on Rotweiler?

Just wondering!

later,
Chuck

 

[canyncarvr]

John:
You are absolutely correct. I missed it.

Apologies tendered. I am lucid on the difference between preload and spacer length. I spedred too fast (and too unwell to boot!)

BTW, my comments re: one measurement being better than the other were in regard to preload, not spacer length. And, absolutely true, preload is largely a matter of personal choice.

Thanks again!


Hell. I wondered why the 'john harris' posts I've read before have always been so exact and correct and informative, so HOW could he miss this?

Well, cuz he didn't miss a thing. I did, though.

Thanks for the correction.

 

[m0rie]

Quote>

From CDave (3-3-03):

It’s the 1996-99 0.38kg/mm XR400 springs that are interchangeable and commonly used in 1995 to 2003 KDX200/220s.

From racetech:
'96-99 xr400r 43mm showa .38
'00-02 xr400r 43mm showa .40


'H' model kawi spec:
'00 200 kdx 43mm kyb .35

<End Quote

I've got a 89 KDX 200, RaceTech's calculator shows it as having 43mm kyb shocks on it as well. Is there any reason that the XR springs wouldn't work in it as well? I was think a pair of the 96-99's would work great for me, i'm about 170lbs with gear, but was concerned about them working in my bike.

-Maurice

 

[canyncarvr]

I'm not familiar with the '89, but the racetech site gives enough information to make me wonder.

For example, the '89 is a damper rod type fork, it seems, as they (racetech) sell emulators but not valves for that bike. The buykawi site shows a valve on the bottom of the '89. I am nonplussed.

That doesn't make a whole lotta difference springwise..but I wonder about the spring length. The 'H' series takes a 3647 (.35 stock) series spring and the '89 takes a 3750 (.29 stock) series.

That's a big difference in spring rate for an interchangeable spring.

I didn't pursue the series differences, but I would certainly wonder about their being interchangeable.

Sorry. That's of little help.

Good luck!

 

[m0rie]

I'd noticed the differences as well. I'm sure that a stock replacement spring from a 96-04 KDX would work perfectly in my forks, Race Techs spring calculator shows both series of forks as using the same replacement springs with a 472mm length. So the question would be if the 89-95 forks can accommodate the additional length of the stock XR 400 springs. I'll dig some more in the forum search and see if I can find anymore info, but failing that there's a set of 97's up on ebay so I'll try and snag them and give them a try.

On a side note, do you ever come over to the coast to ride CC? I'm in Crescent City about 1.5 hours out of Medford in CA.

-Maurice

 

[KDX200Kev]

m0rie,
I have heard the 96-2004 KDX fork springs work really well for pre 95 KDX. The XR400 are way to stiff for pre 95 KDX. I would imagine you could pick up a pair of used KDX 1995-2004 fork springs cheap on e-bay or for that fact on this board.

 

[m0rie]

That doesn't make (much) sense to me. Why would springs that work fine in one fork be too stiff in another? Both Race Tech and Fredette recommend the same springs for all 89-04 KDX's so it would seem that the issue would be length not stiffness. The stock 89-95 KDX springs are only .29 vs .35 for the 96-04 springs. That would be an upgrade over the existings springs but still would be under sized for my weight, unless i'm missing something? The XR 400 springs that i'm looking at are the 96-99 ones (.38) and would be a much closer match, provided they will fit in the forks.

-Maurice

 

[KDX200Kev]

I believe you are correct, the length of the XR400 spring is the issue. I am just conveying what I have heard from others. The concern I would have would be if the XR400 spring length would allow for the proper preload adjustment. I will be interested to read if the XR400 springs work in your forks.

 

[m0rie]

Well provided I can pick up a pair of XR400 springs i'll swap them in and let you know.

-Maurice

 

[89kdx200rdr]

standard fork springs are 496 mm on the 89 so they are longer than the 95 and up springs. whats the length on the xr springs?

 

[Matt90GT]

Originally posted by KDX200Kev
m0rie,
I have heard the 96-2004 KDX fork springs work really well for pre 95 KDX. The XR400 are way to stiff for pre 95 KDX. I would imagine you could pick up a pair of used KDX 1995-2004 fork springs cheap on e-bay or for that fact on this board.

What scientific equation do you base your great knowledge on here?

We have them in a set of 86 forks on a 83 KDX200. Great units there! Ideally they would be about .01-.02kg stiffer, but much better than the stock units that bottomed just sitting on the bike!

 

[Matt90GT]

The spring rate is going to depend on the weight of the bike, rider and conditions. so what works for a 250lb SX guy will not work well for a 150lb wood rider.

know what I mean?

The idea of the XR springs is that they are cheap and up the rates to where they should have been for more people 160-190lbs on these kdx bikes.

 

[m0rie]

The XR400 springs are 530mm in length.
Stock 95-04 KDX springs are 470mm.

Matt90GT -

Thats good to hear that 86 forks will work with the XR400 springs, looks like I shouldn't (hopefully) have any problems swapping them into my 89 forks.

-Maurice

 

[KAY DEE EXER]

I think 570mm- ish ??? Im not 100% sure but someone will correct me if im wrong...

Happy New year to all and be safe !!!!

 

[canyncarvr]

570mm-ish is OK...if your error factor is +/- 40mm! ;)

A US honda spring from the above chart will run around 530mm. I say 'US', cuz there is at least one note on this board from an aussie that said the honda springs HE got were much shorter.

I'm assuming that is a US/other issue. Maybe the springs he got were just wrong.

Mine weren't (wrong). They came from mx-tech, they were in honda wrappers complete with big red wings. They were 532mm. Two oil changes later and they are still 532, btw.

A .35 being way too soft on the 'H' model, it doesn't seem sensible that everything else between the two forks is the same...but the '89 is .29. That would be so far off base as to be just plain silly.