Fork Spring Change - quick question

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Fork Spring Change - quick question

Postby Jeb » 10:07 pm Dec 11 2006

I'm getting ready to install some stiffer fork springs (thanks Wibby!!) and noticed the 0.40s are gonna be about 7mm longer than stock (assuming stock length is right.

Should I reduce the spacer length by the difference?

Also, I've seen the suggestion, more than once, to increase fork oil viscosity a bit - I remember 7W. Thoughts?
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Postby Colorado Mike » 10:17 pm Dec 11 2006

from my experience , increasing the oil viscosity was a bad thing to do. changing the oil was good though. My springs were much longer than stock, so I can't help you there, I unded up going with my own preload spacer that was dramatically shorter than stock.
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Postby canyncarvr » 12:42 am Dec 12 2006

What you should do is set your spring preload to a reasonable amount. That is the point, what the preload is, NOT how long your spacer is.

Unlikely to be more than 10mm, unless you're trying to correct an incorrect spring rate or make up for too many desserts.

The OEM preload is ridiculous..about 35mm.

My preference on the OEM forks (forks that I could adjust preload on) was 3mm, oil at 115mm. You can fairly easily experiment with both to find what works best for you.

If your forks are apart and you base valve is stock, take a couple of 24mm shims off the top of the stack..that rec based only on hearing that everyone that's tried it likes it.

If you have a question about preload, please ask.

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Postby saddletramp » 12:44 am Dec 12 2006

I just started my fork re-buld today, I am putting in some .40 out of a 04 CR 400. They measure 21" my stock springs were 18.5" well, one was a 1/8" shorter. Fredette recomended 10 mm of pre-load for my weight 190#. I figured I would cut a 10 mm spacer out of the stock one but after some research I think you can pre-load the spring during assembley without the spacer.
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Postby Mr. Wibbens » 12:59 am Dec 12 2006

huh? :?
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Postby Jeb » 06:22 am Dec 12 2006

I'm OK with the concept of preload, I'm just not well-versed on the fork internals . . . OK, I'll admit it - 'don't know a darn thing about the forks . . .

Shim "stack" - where in the world is it? Not in the picture below presumably -

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Postby canyncarvr » 11:19 am Dec 12 2006

Re: 'I think you can pre-load the spring during assembley without the spacer.'

You could if your spring was long enough (ie: too long). :wink:

Otherwise, that is why the spacer is there.

This talk of cutting the existing spacer....why? If you want to mess with the metal aspect of it, you're welcome to. Otherwise, 1" schedule 40 PVC pipe is the material of choice. Easier to work with, cut it in a miter box or with a mitre saw, table saw.

The base valve? It is indeed 49116 in the BuyKaw diagram...but you won't see it in the above (when you post a link, it's a good idea to check it to make sure it does what you want it to do).

It's in the lower left corner here:
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Postby Mr. Wibbens » 06:26 pm Dec 12 2006

I think somebody (other than me) needs to tell these yayhoo's how to correctly measure their preload :wink:
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Postby canyncarvr » 06:43 pm Dec 12 2006

No need. A search for 'fork spring preload' will get them lots of information.

Maybe even this!

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Postby Mr. Wibbens » 06:47 pm Dec 12 2006

better than nuttin' :wink:
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Postby saddletramp » 08:55 pm Dec 12 2006

Thanks for the help, forks are back together topped off with Kayaba enzo 1 fluid I have no idea what weight because it does not say on the jug I am sure I will be happy with the upgrade. I also bolted on some mini hi-bends, p.c.2 with guard, 607 reeds and worked on the jetting :supz: :grin:
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Postby canyncarvr » 03:07 pm Dec 13 2006

Jeb started this thread. How YOU doin'? :wink:


'Topped off' doesn't mean topped off...right? What preload did you decide to try for starters?

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Postby saddletramp » 04:22 pm Dec 13 2006

Kawie tech said 625 cc's so I went with that, with 1" spacers. It looked like you (carvr) just did this same conversion so I figured that you new what you were talking about
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Postby canyncarvr » 06:42 pm Dec 13 2006

Ha! That's funny!!

On so many levels....

The 1" is the DIAMETER of the pipe, NOT THE LENGTH OF PIPE YOU CUT!!

The preload is a PIECE of 1" diameter SCH-40 PVC that you cut to the preload YOU desire.


I'm sorry...the juxtaposition of parts of things said over years of time that had to be juggled to come up with, 'Use a 1" (long) spacer for preload' (for a 545mm spring!!!) is pricelessly hilarious!!!

And...I haven't just did this conversion..unless 4-5 years ago is 'just'.


OK...I've caught my breath from guffawing...

If your spring measurements are correctly stated and the spacer you used is indeed 25mm, what you got is 40+mm of preload. I didn't check the math..suffice to say you're WAY OFF!!

That's worse than the OEM spacer!!


Where that will really be a problem is, you're not using 21# springs no more!!

You have NO free sag..probably no RACE sag on your forks. It's going to be terribly rough, you will have NO control in corners, the front end will be a very very bad POS...and that does NOT stand for Point Of Sale.

Actually, you didn't say what you weigh. If you're 320# or so, you might be OK. :blink:

Take them apart. That will include draining the oil you just put in.

Take out/off the spacer and the two cupped washers. Reassemble. Thread the cap all the way down on the rod. It does not have to be tight, but it does have to be snug. Don't worry about the jam nut, but don't let it interfere with the cap going on all the way. If you take the cap off as most do, the rod will be jammed at the bottom of the rod threads, so it shouldn't be a problem.

So...you have the spring and the cap on the rod..no spacers or washers. Pull the cap and fully extend the rod. Don't worry about the tube. Measure the space between the top of the spring and the bottom of the cap. For sake of argument, let's say it's 25mm. Measure the flange of both the cupped washers..let's say they measure 3mm.

Those washers are going to take up space in the final assy, so you SUBTRACT their thickness from the measured value. That gives you...what?

22mm.

IF you cut a piece of the PVC to 22mm, you will have zero preload.

Sooo..preload will be whatever is longer than 22! A 32mm piece would give you 10mm of preload.


All of the above is considering that you have springs that fit in your forks.

You said your springs measured 21.5". That's 546.1mm in my book.

Again, IF your figures are correct, you would have 15mm preload if you assembled the fork with NO spacer...and NO washers!!

No spacer isn't a problem. No washers is.


What we have here is failure to communicate!!

But you DID figure correctly. I DO know what I'm talking about.

Cheers!

**edit**
Yanno..actually it will probably be just fine..the springs coming out of a CR400 and all. As long as they are out of an '04!

Oh no....I can't breathe!!! :shock:
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Postby Jeb » 07:59 pm Dec 13 2006

'Think I'll make the swap tomorrow evening, maybe Friday; I'll go with the PVC cut to provide 10mm of spring persuasion. Then I'll go beat it up some this weekend - 'gonna be NICE on Saturday!

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Postby saddletramp » 10:57 pm Dec 13 2006

Geeze, breathe already. Good thing I didn't brag about how great my new springs handled I really would have looked foolish :oops: I should have read more carefully. I ended up with a 7mm spacer with the stock washers should put me at 8 or 9 mm pre-load or so. I had about 7mm of sag when I sat on the seat, is that about right?
Thanks for the post Jeb good timing. :mrgreen:
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Postby canyncarvr » 11:41 pm Dec 13 2006

I left all my math homework at the shop :? ...but I think a 7mm spacer will still give you over 20mm preload. Again, that is based on the stated 21.5" length of your spring which doesn't sound right.

Race sag for forks (loaded..you on it) runs more like...uh...I always forget. Somewhere around 30-40mm I think. I sure this isn't a correct number! At 7mm, you have too much.

I can tell you this: (personal story time) With my XR springs in my OEM forks, their was a considerable improvement when I changed from a 10mm preload spacer (not a 10mm spacer...a spacer that got me 10mm preload) to 3mm preload. The bike stopped crabbing on rut edges and tracked a whole lot better. It actually went where I pointed it!

Remember there is NO rebound control on the OEM forks outside of oil viscosity. So...if you're too tight on the front end, when it comes time to rebound..you won't have very far to go.

The 'add x volume' of oil thing isn't a good idea. The amount of oil needs to be determined by measuring how far down inside the tube it is. 100mm is the general rule of thumb, but you will be happier with 115mm. imo and all that.

Do that with the spring out, fork collapsed, no bubbles (make sure your forks are bled before you check the level). Use a large animal syringe (from your local feed store) and a piece of tubing to remove the excess oil to reach the desired level.
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Postby saddletramp » 12:05 am Dec 14 2006

I only had 2mm from top of spring to bottom of cap, so.. 1 washer went in flange down inside spring=1mm + 7mm spacer + another washer flange down into spacer=9mm minus 2mm = 7mm pre-load, that was with the tubes still in the bike, bike on a stand. Not sure what visc. fluid is it just said enzo-1 kay. cart. forks .
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Postby IdahoCharley » 12:34 am Dec 14 2006

On our stock KDX forks with XR400 springs I used PVC spacers of about 8.5 mm as I recall to give us a preload of about 5-6 mm as I recall from memory. Preload sound to me to be in a workable range.
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Postby saddletramp » 01:01 am Dec 14 2006

Yeah, I did some searching and it seems to be about right. I need to clarify that the springs were out of a 04 XR 400R not CR. And I found the correct way to measure sag.
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