KDXRIDER.NET

Hey all
So I went for the first ride the other day with the 49mm showa's from a 99 rm125 and while it tracked very well and was awesome on the whoops it was pretty harsh and I had some serious arm pump buy the end of the ride. Some of that pump may have been the first ride thing but the forks were only using about 2/3 of their travel.

I did a little rip n tear today and looked at the compression assembly. It has the valve with shims which rides in the rod inside the spring. Also I saw a second chamber above the valve where the oil goes after the valve. This chamber has a piston with a spring above it that I think compresses when the fork is in it's last 3rd of travel. It seems to me that it's for big hit dampning.
Does that sound right??
I removed the piston and spring and also 2 of the large shims from the valve from each fork leg and now it feels like I'm actually getting some sag, both static and with me on it. It also feels more linear in the travel until the last 3rd where I just can't push it anyway. I think with the shims out that my clicker will work better for me as it was all the way soft before anyway.
So does this sound resonable or am I way off here?
Cheers
fletch

It sounds like the spring rate is too high. Changing springs may put you in the hunt without mods.

I have the DRZ units, and the springs are about right for me for HS training. And at 230# I can't quite bottom them out when I push them hard. I haven't really started working on fine tuning them because I need to take the ice screws off and I have been busy rebuilding my kid's bike from the frame up.

I am not that familiar with the internals but I know the RM units have a relatively small compression valve. Your shim adjustment may be the right thing to do to get the ride you want. Keep us posted.

Thanks for the reply gsa102. Seems our lives are paralleling as I just took off the ice tires and just finished a good overhaul on the kids pw50!

I did a bit more reading and it seems the piston spring combo is to stop cavitation of the oil in the upper chamber. It's akin to having bladders in the forks from what I understand.
I think you're right about the springs though. they have .40's in them now and I can go as low as .39's according to racetech's site but am not sure if that's a big enough jump. Racetec's site says .47 for me! I think not...

My concerns with the piston removal is 1. cavitation. 2. that the oil may spill out of that chamber when the bike is on it's side.

Does the bladder set up on the kx's if removed allow oil out of the upper chamber? Or does it remain sealed up and contained??

Fletch - You haven't mentioned your weight. Since RaceTech is recommending .47s, I'm assuming you are over 200?

Do you have a picture of the piston you removed?

Did you hit any jumps and only use the 2/3 travel? If so, about how high were you jumping?

I'm about 185
A general pic of the same type of fork, the piston is inside the cylinder directly under the top caps.
http://www.supermotoaus.com/showthread.php?t=6576
No jumps for me, I'm not a jumper but some good whoops and harder rock hits.

I don't have experience with Showas, but it sounds like you are describing that you removed the piston from the base valve. If that is correct, you shouldn't ride the bike until you can put those back in.

I'm about 190 and was able to bottom out my KX forks with .44 springs (the online calculators suggested the .44) on little 5 foot jumps.

For your weight, you don't want to go with a lighter spring. If anything, you need heavier springs.

Springs hold you and the bike up, valving is determined by the type of riding you do. Having too light of springs can actually cause a harsh ride b/c the forks are riding too low in the stroke.

Put the pistons back in and try a few things before spending money on new springs.

What oil level are you running? Too high of a level can cause a harsh ride and prevent the bike from using all the available travel. I would try running the minimum oil level and see if that makes things better. You can always add oil and re-test.

What about your midvalve? Did you make any changes to that? The MV contributes a great deal to the performance of the forks. So small changes there can have a big impact.

If you are not doing any kind of jumping, I wouldn't expect that you'd be using up all the travel. I think it is reasonable that 1/3 would be left if you are hitting whoops and rocks.

Only recently have I used heavier springs (.48's) and I really like the difference they make.

Ok I'll do that. I can leave the 2 shims out of the base valve though no?
The piston's are easy enough to put back in but how do I access the midvalve???

I'll try the forks with the minimum oil levels with the piston's in and leave out the 2 shims. I'll report after that ride test.
Thanks!

Just trying to confirm which piston you removed. This is a base valve from KYB forks, but should look similar to your Showas. You would definitely need to put the piston back if you removed if from this part of the forks.



Removing some large face shims shouldn't be a big deal. Removing other shims can have a more dramatic impact.

Had the forks been revalved or where they stock? If the nut was still staked or peened on then they are stock. If they have already been revlaved, you may want to see how far from stock you already are. Making changes to an already modified stack may make things worse.


The midvalve is on the end of the cartridge rod. These are KYB forks, but again should look similar. The midvalve is on the left hand side of the cartridge rod. Once you have the base valve out, the cartridge rod slides right out.

Yep that's the piston so I'll put it back in. The forks have been revalved at some point as the peening was ground off. I know exactly where those valve shims go and can put them back in if needed however my compression was already dialed right out and was still too firm in the tight stuff.
I'll check to see if the midvalve comes out as easily on the showa's as the kyb's. I see that the kyb's also have a much larger base valve.

Thanks a lot Tedh. I hope others can learn here too.

Does the bladders on the kx forks do the same thing as the springs/piston combo shown above? Just cause I hear of some disabling them and am wondering if doing that can cause cavitation?

At this point I'd suggest you do some research on your forks before you go any further. There are little things you need to do when pulling the forks apart and putting them together. Like wrapping the cartridge rod threads with teflon tape before you remove them, bleeding the cartridges of air, etc.

I'm not sure how much info is on this site about those forks, so you may want to try TT.

Another important thing you need to do is document exactly what shim stacks you have in both the base and mid valves. You also need to measure the float on your mid valve. Then you can compare those to the stock stacks to see exactly what you are dealing with.

Pulling shims from a modified stack is going to be hit or miss. For all you know, you current stacks are too soft and that is causing the harsh ride.

The one thing I've consistently read is that no valving modifications can compensate for an improperly sprung bike. As I mentioned before, I think your springs are already too soft and can be causing the harsh ride. An RM 125 is a lighter bike and intended for a lighter rider. Those .40 springs seem too weak for your combination now.

Ok, Tedh
I've been researching the forks but info's a bit tricky as they were only used for a couple years. I do however have a rm manual that has the tear down and re-assembly info although it doesn't delve into the valving at all.
I have taken a leg down to the midvalve and it's in stock configuration. I'll count and measure what I have in the bv and compare it to stock if I can find it. I am re-installing the pistons and springs above the bv's and am not monkeying with the mv's yet. I was looking at them though and I think from what I've been reading that I have a check plate on one side and the rebound shim stack on the other. The rebound stack appears to have 3 large shims across it and that's it but I'm not grinding off the peaning to see for sure. Tell you what though, I'll take some pics.

Wait, upon closer inspection the mid definitely has shims on BOTH sides.
Pics

Am I right to think that the bottom pic is the rebound stack and the second last pic is the mid compression stack?

Fletch wrote:Am I right to think that the bottom pic is the rebound stack and the second last pic is the mid compression stack?

Correct. And said a different way, the shims closest to the nut are rebound and the shims furthest from the nut are compression.

Ok I changed the oil (obviously) on that side with some 7.5wt I had around. 325ml is the min for the fork and then filled the cartridge chamber to spec. I'll see how it goes using the clickers.

With so few shims on the mid compression side, what is the purpose there instead of shifting the compression duties to the base valve? The rod is much harder to pull up (rebound) than compress.

There are a number of posts on TT that explain the role of each component far better than I could do. The mid plays a huge role than what you would expect just from looking at it.

When you get a chance, pick up some 5 weight oil. I think you'll like it better for the woods.

I'll check it out and report back, again thanks Tedh for the help. I'll start shopin for some 5 wt too.