For Forks Sake!

So I last did a fork oil change about 2 years ago and 15000 miles or so hence it's time to do it again. I used 10w before and this helped with my saggy forks but thinking of increasing the weight to 12.5 , is this a good idea do you think?

Just to reiterate I am 80KG and have always cited the forks as the Swings main issue as it bottoms out on all but the smallest of bumps , drain access covers and sleeping policeman, yes its that bad check out my Youtube video if you think i'm exagertaing.

So this time I will measure the springs for the service limit as I guess after 21 years of carrying that bulk the oe springs are bound to shorten a little ......I just measured my forks for travel and this is what i found ...

Off the ground. no weight - 130mm
On the ground, bike weight -95mm
On the ground, bike and rider - 90mm

Houston do we have a problem? I'm not sure but the next time it bottoms out (tomorrow) I will measure the bottom out limit of the forks but I guess its going to be about 40mm and not much more.

I have already tried stacking some washers under the spring and probably around the 10mm so I guess I am taking away some travel for some increased compression so the bottoming out could be even worse.

the vid link, apologies for the profanity but this as before I serviced the forks..

https://www.youtube.com/watch?v=BYCUgyXfeJs

According to the service manual the fork travel is 120mm, and a reasonable rule of thumb is for the bike to use 25-33% of the travel supporting itself and you, so that would be up to 40mm of travel. If I have understood your numbers, you have exactly 40mm travel used so that's a decent start and gives 40mm of extension for the wheel to fall into negatives like dips and holes.

The spring rate plus preload is what will determine whether you bottom out or not on bumps, and you can add more preload (and lose some of that 40mm travel), or you can install stiffer springs, or you can also increase the volume of oil in the leg (or any combination).

The air over the oil inside the leg gets compressed when the fork travels and you can harness more of that compression by reducing the air volume, which will increase bottoming resistance.  The standard oil level is 97mm (forks compressed, springs out) from the top of the tube, but by way of a contrast my ST1300 specifies 62mm air gap.

Boosting the oil weight will provide some more bottoming resistance but you run the risk of harshness if you take that too far.

Here’s a link to a very informative recent discussion regarding front suspension mods you might find helpful.

https://www.silverwing600.com/t12580-fork-springs-mod-poor-mans-hyperpros?highlight=Front+suspension

I redid my fork seals a couple of years ago and used 10w oil and it was terrible... That is what the book called for but it was way too soft. I weigh in the 240 lb range. I switched to 15w fork oil and it works OK. Not great as the forks have never been the best but certainly works for me. Good luck.

In the link that Tim posted above, I had asked a couple of questions before going ahead with the Stefan Bonacasa front fork mod. Since then I've done the mod with the extra springs and used 15w Motul fork oil as advised by Stefan. I'ts made a noticeable difference. The front suspension doesn't crash into or bottom out on potholes like it used to. My Swing is now more pleasurable to ride.

cheers will source a spring or make a spacer i think, the washer in the link looks quite expensive all things considered and i guess you could get a 25 pack for the same money at a hardware store...

I bought these, I’m 260lbs, love them!
https://epmperf.com/product/fork-spring-kit-honda-fjbs-600-silverwing

K-Hill wrote:

I bought these, I’m 260lbs, love them!
https://epmperf.com/product/fork-spring-kit-honda-fjbs-600-silverwing

Would these be the same for a 2011 FSC600A? I weigh about the same and have had a couple of bottom outs as a single rider. I have no idea if the forks have been touchedby the PO. And if I am going to crack them open I might as well adjust them to my size.

OK so like I said a few days ago I managed to fit the rebound springs and replace the 2 year oil in the fork legs, first thing is that with the 300ml of oil in the leg with the air expelled I have about 55mm from the top of the tube. Not sure if there is some residue in the bottom of the leg or if the 02 legs are different in design but hey thats close enough guess.

Springs in and a washer between the spacer on top was a bit of an issue to get the screw cap back on but 4th time it caught the thread and wound on.

The ride now is firmer , harsher yes and it still clunks out over bigger bumps but a lot softer then the crash bang wallop i used to get with only the original spring in place.

I do have a few other bikes , a 96 transalp for one and although i realise the fork travel is far greater the fork tube itself is smaller and the oil has not been touched for a very long time and I get perfect travel and hardly notice the pot holes, the fork performance is chalk and cheese between these bikes.

For the money I think its a good easy mod and maybe playing with the oil height and weight will produce even better results. I would be very interested to try a SWing with the hypro springs installed so if any UK inmates are riding out in the central shires one day please let me know. I also attend big bike meets like Motogp and WSB so maybe hook up there sometime.

Cheers Peeps

cello33 I would guess at the moment according to your figures that your forks are oil bound hence the harsh ride, With the springs removed and after pumping the forks and leaving fully compressed you should have a minimum of 90mm left between the oil level and the top of the fork tube as an air gap for correct operation of damping. But..
TBH having tried the mod your talking about (I was going to do an article but)it is an improvement, but no where near as good as fitting Hyperpro springs with 20 oil(they provide). They are true progressive springs and they will transform your ride! Seriously!



Suzki AN 400 1999
Honda Silverwing 600abs 09

Be safe, be seen!