Fork Spring Identification

I bought some forks off an '06 YZ450 and am working on them tonight to check them out, change the oils, and re-spring them.  I have Race Tech .50 kg/mm springs in my WR forks that I put in about 9 months/30-ish hours ago, and my original thought was to put the stock springs back in the WR forks and throw the .50s into the YZ forks.  Then just as I started working, I thought about the springs that are already in the YZ forks - is there any way to determine what rate they are?  I only ask because although it does not appear that the forks have been apart before (based on the lack of tool marks anywhere on them), somebody did put some Enzo Racing KYB stickers on them and that got me wondering.  

I know factory shock springs usually have a paint mark on them to denote their rate, but not sure about fork springs.  Could I tell by measuring or otherwise comparing them to the stock WR .46 (I believe) springs?  


Thanks for any help.  I will post what I find in a bit.


edit: quick trip to the Enzo website reveals that if they do set up forks, they use genuine KYB springs.  Not that I think these forks have been worked necessarily, because anybody can put stickers on stuff, but just hoping to be able to ID what's in them if they have been worked.

Edited by RockerWR450

Well, the YZ spring (on the right) is definitely shorter, about 8 mm, than the stock WR spring, which tells me higher rate. Pretty sure they were a higher rate than the WR springs anyway. Total length is around 451 mm. Any ideas?

Onto RT spring removal from WR fork to compare.

Yamaha marks their springs with dots of paint or stripes or grind marks.

The Service manual explains it.


Aftermarket springs aren't usually marked in my experience.

Thanks for the reply. I didn't find any markings at all on the springs, so I went ahead and pulled the RT .50s out of the WR forks and put the stock springs back in. RT actually does print the rate on one of the coils as I found out.

Now I just need to know if I'm bleeding the IC correctly. I'm following Dave J's method as closely as possible, but the damper rod still stops with another 50-ish mm to go to full extension. He mentions 20-60 mm on his site, but if I keep pumping the rod with the assembly horizontal, it will continue dripping and that unused travel distance becomes greater, even to the point of sucking back in a bit if you do manually extend it all the way.

When it's first bled, it seems to be fine, but if I keep messing with it and it loses more fluid, it loses more travel. I thought the IC was supposed to be sealed from the OC?

Anyway, I know there's much written about this - I read a lot before starting the job and then read more and watched videos during when I ran into this issue (if it is an issue at all). I still have the first fork all apart and will read everything I can find today and figure out if I'm doing anything incorrectly.

I may just need to bleed it once, stop messing with it, and put it back together - I just don't want to set my oil level carefully and then have a little bit drip out into the outer chamber.

Eibach springs were always printed the the part number, which actually read the rate, if you knew how the number worked, but that would come off pretty quickly in use. 


The YZ spring is not very likely a higher rate just because they're shorter.  In fact, it's very unlikely that they'd be .50's unless the guy you bought them from was up around 250 somewhere.  Wire diameter is different.


There's a way to make a fairly accurate calculation:



Dw = Wire Diameter
Dc = Center-to-Center Coil Diameter
Ca = Number of Active Coils

The answer is given in N/mm. Divide that by 9.81 to get Kg/mm, or use this:


Number of active coils is how many full circle coils of wire there are between the end loops; coils that are not touching another part of the spring.


Wire diameter is the measurement that has to be accurate.  Very small changes in wire size have a major effect on the rate, so if you want a good result, be precise here.


The center to center coil diameter is found by measuring the OD of the coils at some point away from the ends, then subtracting the wire diameter from that figure.

That's awesome - thanks a lot for that formula.  I will figure out what it is when I get home later.  On a related note, if I'm 200 lbs with no gear, ~220 with gear, do you think I'll be over-sprung at .50 with the dual chamber forks?  I went .50 with the open bath forks because that was what RT recommended at the time.  As abusive as I am sometimes in deep whoops and flat landing jumps, a little extra spring rate may not be a bad thing. 


On an unrelated note, any thoughts regarding my IC bleeding issues?  Am I over-thinking/working it?  I have done everything I know to be possible to ensure all bubbles are out of it.  I just want that thing to not drip out its bleed holes and still push the rod out to just short of full extension consistently.

The fork type or design doesn't really play into what the correct spring rates are.  If you liked the bike with .50's in it before, you'll probably like it that way with the new fork, too.


As to the bleed process, I elaborated on this a bit here:


But, even if you don't get all the air out, the cartridge should not continue to expel oil on more that perhaps two successive full compressions.  The way it work is that the free piston is lifted by the oil displaced by the damper rod as the cartridge is compressed.  If there is too much oil present, the piston will rise until it clears the the bleed hole, and the excess will be exhausted.  After that, there should be no reason for the piston to be able to rise to that level unless more air or oil enters the cartridge from somewhere.  In your case, you may have a leaking seal allowing air in when the rod is extended.  The culprit would likely be the seal at the bottom of the cartridge around the rod, and might be aggravated by compressing the rod too quickly.  That would, of course, happen in use, too, but it would slurp oil from the outer chamber, rather than oil, and the excess would be exhausted on the next near-bottom stroke of the fork.  Something that needs to be fixed.  The free piston seal around the base valve stem may also be at fault.


Also, read this regarding a confusing point about reassembly:

I did read your article from the first link previously and just re-read it.  I think part of my problem may be that after I run through a couple of vertical bleed strokes (with good effects), I've tried pumping the damper rod with the cartridge assembly on its side, and a bleed hole over my ratio rite and then wonder why it's still dripping, thinking it should be completely sealed in the cartridge.  I'm not sure that some of the oil isn't just the remainder draining out from the free piston area (which I did modify with one 5 mm hole on each side, about 15 mm up from the bottom).  But the loss of damper rod travel following that little exercise is noticeable, starting at around 30 mm just after the bleed, and ending up over 60 mm. 


I did talk to Terry at Race Tech earlier, and for what it's worth, he said a few inches (which would be up to around 76 mm) was not a big deal. 


I will pull the cartridge apart tonight since it's still out of the fork and take a look at those seals.  As you said, they might be a culprit as well, since even after two full bleed strokes, I still get a little bit of oil weeping out the bleed holes.


Thanks a lot for your help with this.  I hope I can get this figured out tonight.

As long as I got my order of operations right, the measurements I got work out to a .4719 kg/mm spring rate for the springs that came out of those forks, which I believe is the stock spring rate for the '06 YZ450. That answers that - the online calculator link did not work for me, however.

I also reworked the IC that got the best of me yesterday. I focused more on twisting the compression valve assembly with more fluid (about an inch above the holes) with the whole thing at an angle and making smaller and slower movements with the damper rod while working the valve in and starting its threads. Slower is faster in this case. I have no air in them at all now, they push out with about 25 mm to go, and once I patiently let the bit from the free piston area drain out, they do not leak at all. I should be good to go.

I went with 350 cc of 7 wt in the outer, so I'll see how that works out.

Thanks again for all the help.

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