Fork Spring Swap

K

kkmann

contributing rider
Joined
Feb 3, 2021
Messages
15
Location
Tellico Plains TN
Finished up the fork spring install this morning and made a 100 mile ride! SOO much better, smooth, consistent action. Springs are Race Tech S3732 series, 0.85 kg/mm. RT recommended 7mm of preload, so that took a 30 mm spacer (they include tube spacer material, cut to fit). You can see the new springs are shorter than the original ones, which do not have any spacers installed with them. One oddity, I had to cut one coil off the new springs. You can see on the end on the table the coil diameter suddenly decreases, so it's too small to fit. Thought that was kind of weird.

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this pic shows the new springs are just long enough to get to top of damper rod, but the fork cap screws on there, and so the spring is 23mm "too short", hence a spacer is needed.

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Sag is excellent now at 37 mm rider sag (26% of travel), whereas OEM is was 69mm for me. This pic shows what rider sag is now.

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Here's a couple pics from my ride today. You can see in first pic what the max fork travel was so far about 50 miles in, and that included pretty bumpy paved roads, dirt/gravel/rocky roads, popping over a few rocks, a 3-4 inch log, etc. So really happy with fork living in middle of travel with good consistent action. I've now removed all compression damping and I'm at only 2 or 3 clicks of rebound damping (from all the way out).

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I was going to put in better seals and wipers anyway, but my right fork leg was already leaking by 300 miles so glad I had that planned. The SKF set for WP 43mm forks fits perfectly. New fluid is Amsoil Shock Therapy light (5#).

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You'll need some "special" tools. I made a 45 mm hex wrench for the fork caps (left over Al plate). Fork caps are not on tight, you don't need a "real" wrench. Had to make another jam nut "wrench" for the damper rod (22mm, wrenches that big are too thick). And I had to take one of my 2-inch PVC pipe seal drivers and heat it up with a heat gun to make it a little smaller for the 43mm forks.

IMG_8008_HEIC-L.jpg
 
I've been wondering how much travel the front fork really has. Any chance you measured that?
And does it have a soft bumper at the end?
 
No bumper, unless it's really minimal and internal to the lower section of the damping cartridge. But when the inner rod hits bottom (like its' sitting in the first pic above) it's solid, it's not the least bit bouncy like there's even a little bit of rubber. The fork tubes will meet all the way to where the wiper meets the bottom of the lower leg, but I doubt it will stroke that far, it's limited by the distance the damper rod will move. I didn't measure that while I had it apart, that would have been easy tho, doh! Race Tech has the stroke value at 142 mm, which I seem to recall reading someplace else too.
 
I've also seen 142mm in the manual... but I've found I haven't gotten near that, so I've been wondering if it is correct. The most travel I have seen is around 125mm.
I know the rear travel is limited to significantly less than advertised by the rear bumper.
 
Vintage Veloce said:
I've also seen 142mm in the manual... but I've found I haven't gotten near that, so I've been wondering if it is correct. The most travel I have seen is around 125mm.
I know the rear travel is limited to significantly less than advertised by the rear bumper.
Click to expand...
It's because the final rate is so stiff (and doubly so for such a light small bike), that's basically the "bottom"
 
kkmann said:
It's because the final rate is so stiff (and doubly so for such a light small bike), that's basically the "bottom"
Click to expand...
Yeah, that makes a lot of sense from your picture of the stock spring! The stock spring has a lot of tight coils that can bind up making it much stiffer. Great info!
 
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I am getting ready to do my springs now that the garage is above freezing...

When i open the cap and then take the screw out of the bottom, the cartrige slides out, right?

Then the springs just slide off the cartrige and the new ones can be put on in their place.

Or is their someting I missed?
 
BISavage said:
I am getting ready to do my springs now that the garage is above freezing...

When i open the cap and then take the screw out of the bottom, the cartrige slides out, right?

Then the springs just slide off the cartrige and the new ones can be put on in their place.

Or is their someting I missed?
Click to expand...

Mostly right. The fork cap must be unscrewed from the top of the damper rod, the jam nut is that silver aluminum "nut" you can see at the top of the spring in pic 2. It's actually attached to the black plastic inner bushing as a unit, they screw on to the damper rod as well. So you gotta hold the jam nut to break the cap off (they aren't "that" tight). That's why I made the 22mm slot wrench out of plate aluminum, my 22mm wrench was too thick.

With both the cap and bottom bolt (which is quite the odd size at 7mm hex (Allen key)) it's always better to "break" them with the forks clamped into the triple clamps. Way easier than trying to hold them in a bench vise. After that it's just easy hand disassembly.

Of course the springs will have and need a little bit of preload, so you will have to muscle them down far enough to get to the jam nut. Luckily it's not that much of a struggle with fork springs.
 
Now when replacing only the springs & oil and not the seals, only the top cap needs to get opened, and the cartridge can stay inside, right?
 
BISavage said:
Now when replacing only the springs & oil and not the seals, only the top cap needs to get opened, and the cartridge can stay inside, right?
Click to expand...
True. It might be easier to take the cap off and replace spring with the cartridge out, but there's plenty of working room leaving installed. However, if you get to the point you are changing oil because of age, I'd certainly take the cartridge out so you can clean the inside of the fork tubes better, there will be gunk at the bottom.
 
I figured that since its only 1 year old with 8k miles i would do the just springs and oil now, and by the next maintenance/oil change at 2 - 3 years of age I would take it completely apart.
 
kkmann said:
Finished up the fork spring install this morning and made a 100 mile ride! SOO much better, smooth, consistent action. Springs are Race Tech S3732 series, 0.85 kg/mm. RT recommended 7mm of preload, so that took a 30 mm spacer (they include tube spacer material, cut to fit).
Click to expand...

How much do you weigh?
 
So, I did the front springs today.

Walk in the park.

Couple of things to note; as kkmann pointed out, a normal wrench doesnt work so I bought a cheap one which of course was very thin, thin enough to fit. Next, needed to enlist some help for putting the caps back on.
Also would like to point out that grease for the seals made me say "wow" because of how much difference it made.

The cheap wrench can be seen in the middle.

20210320_223200.jpg
 
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