mid-valves are my problem?

[Quantumcanuck]

This is the deal :)

I have a 2003 KX250. I have zero control over rebound or compression damping. I sent my cartridge valves to MX-Tech and they rebuilt them. It was thought they were contaminated or had a warped shim in them. They found a warped shim in one but they noticed it had scratch marks, like from a screw driver, on it so I'm not sure if I did that when I was in there messing about or the local shop did it by mistake.

I reinstalled the cartridge valves and made sure everything else was super clean before reassembly. Filled them up with 5wt at 120mm and went for a ride. Same thing. I was blowing through the travel so easily and the front was bouncing right back. No damping either way practically.

Somebody suggested my compression stack/valve assy's were at fault. I figured I try and see what I could do (again) so I bought and installed Gold Valves. The instructions highly suggested that I convert the mid-valves to check plate style so I did. I built up the base valves exactly like the instructions said and put 'em back together and went for a ride. A little different feeling but still not right and still no control over damping with either adjuster. All the way in or all the way out, makes little to no difference.

So now I am back to thinking it's my mid-valve piston bands. They are one continuous solid piece, not like the broken type that look like they just wrap around the mid-valve that I see in ads on the net. The are made of very hard material and have the look of smooth cardboard to them. I can also get them to move back and forth a little while they are in the cartridge tubes so I really don't think they are sealing tightly against the walls. I can actually see light on the other side a little if I lightly push the valve to one side. I think the combined slack around the piston band is much more than the area made by backing the rebound needle out.

So... I'm wondering if there is supposed to be a teflon coating on these bands that may have been worn right off some how or if they are just messed up in some way? I did winter ride the bike for a season a couple years ago. Maybe that did something to them.

Sadly I can't purchase just the mid-valve assy's, they want me to buy the complete cartridge assy's and that ain't happening. I'll go buy another bike before I drop that kind of coin on this thing.

So does anyone know if my piston bands are worn? Are they supposed to be rock hard and have a brownish finish to them? I thought they would have coated them with teflon.

I am also thinking about buy piston bands from an '02 model. Maybe I can ditch the ones on my mid-valves for some new '02 ones and see if a better seal does the trick. That's assuming they'll fit of course :(

I know one thing. I hate my bike because of the forks. It's a chore and a pain to ride it fast at the track and cornering is crappy as well because of the poor action of the front. My buddies 2000 CR250 feels so plush and controlled compared to my bike and as plush as it feels and can't get it to bottom. That's what I want.

Any ideas?

John

 

[marcusgunby]

It sounds like you must have some blow by the piston ring, they are hard and brown looking so yours sound normal, it doesnt sound normal to have light passing by the piston ring however, one other thing to consider is the 03 has a cylinder valve, this is designed to let air escape from the top of the cartridge to give more consistant damping, maybe yours has gone soft -this is common on the YZ type kyb with a CV.RT make a block off kit for the yz fork but i would not advice using that idea.


The only idea i have it too source a new piston ring, mx tech should be able to find one of similar size, you can even cut them to size if they are too long.You just need the right height and thickness.

 

[Quantumcanuck]

Thanks for the fast reply.

My only concern with using the broken type of piston band is that I think there is supposed to be an o-ring underneath then as well. I see other mid-valves have a cut out for the o-ring to go on first before wrapping the piston band around. I'm not sure but I don't think my mid-valves have an o-ring sitting under the piston bands. I'm worried that trying other type of band without an o-ring under it would cause it to not work properly. I'm wondering if my mid-valves even have that groove machined into them for an o-ring.

As for the cylinder valves, those are the cartridge valves that MX-Tech rebuilt for me so they are good. I'm never sure what they are called exactly.

What are those other piston bands made out of that you can just cut them? And why are mine hard like rock? Different style now or something?.

Thanks

John

 

[Quantumcanuck]

Oh, and I almost forgot to inquire about this.

On the Gold Valve website it has specific instructions for my bike and kit. It says:

"Replace Mid-Valve o-ring with check spring provided. Convert Mid-Valve to Standard Check Valve. Remove piston ring from cartridge seal head."

What does "remove piston ring from cartridge seal head" mean?? I didn't see anything that looked like a "piston ring" on or near the seal head. And what's a seal head anyway?

I called them numerous times and no one ever answered the phone so I finally did what their machine asked and left a message with my question and my phone number. That was 2 weeks ago and no call back. I even emailed them asking them the same question and no response to that either. I won't ever be dealing with Race Tech again .

I gotta say, Jeremy at MX-Tech you run a proper business. It was so nice dealing with you and your company the first time that I'll always be going back to you guys. Customer service really does make a massive difference.

 

[marcusgunby]

I think they are refering to a older model that used a o ring to preload the midvalve shims.That was in 2000-2002.

I wish i could help more but i have never removed the piston band myself so i dont know whats under it.

If mx tech have done the CV then you must have blow by?

The piston bands appear really hard until they are removed.


The piston ring on the cartridge seal head is the white ring at the top, it disables the bladder when you do this.

How about taking them to a local suspension dealer/tuner for his opinion?

 

[marcusgunby]

Had another idea.One easy fix would be a 7.5 or 10wt oil.

 

[Quantumcanuck]

The only guys I am told are good in town here already had a go at it and they didnt make any difference. I'm gonna think about it for a while and see what I come up with. I can't blow anymore coin on it. I'm back in college again.

 

[KTM-Lew]

Who assembled the forks? I'm assuming you are sending parts out for inspection and then assembling them yourself? Sounds like you neeed to send the complete forks to Jeremy and let him see whats going on. This stuff isn't that hard to figure-out......

I'm guessing to have the rebound mid-valve piston flipped over or something like that? Does the KX use the 2-piece piston like in the Yamaha? I really doubt the piston seal is worn-out enough to completely make the rebound clickers inoperative. Something is assembled incorrectly IMO.

 

[marcusgunby]

They are a single piece piston, i have a friends, his is valved stiffer than mine, yet its alot softer and bottoms alot, i think they vary alot in production.A thicker oil would offset any blow by IMO.

 

[KTM-Lew]

I believe MX-Tech sells the sealing band for the piston. You cut the old ones off and heat the new ones in water then slip them on. Once cooled they shrink to fit. On rebound the oil has to go thru the valving, bleed (clicker), or leak out the top of the cartridge thru the bushing/CV, right?

It amazes me that some people make this stuff so difficult. He should be able to tell if the cartridges are producing damping when they are being bled?

Sorry.....I guess I need to take a break from this stuff........

 

[marcusgunby]

They may well make some damping but not enough.

 

[Quantumcanuck]

When I bleed them during filling they produce a noticable damping effect on the damping rod as I push and pull it, but against the force of the springs pushing against them they don't produce nearly enough damping.

I have changed the the base valves with Gold Valves, the cartride valves have been rebuilt (bushing, seal and shim each) and the mid-va;ve has been converted to check plate style as per Gold Valves instructions. The stiffer shim stack is at the bottom of the mid-valve and the check plate is on the top (I hope that is the way it's supposed to go). If I remember correctly, the check plate on the base valve faces upwards.

So, with these listed items either replaced or rebuilt, what else is left? All I can see that would cause loss of damping control in either direction is the piston band around the mid-valve.

These particular bands on my KX are rock solid and can be rotated around the valve itse;f with my fingers. I wondered how they got them on in the first place but after reading the post about them expanding in hot water then shrinking again, it makes sense to me now. They certainly can't be pulled off the way they are now.

So, I have no idea. No one I talk to has seen the piston bands wear but what else can cause my problem?

 

[russ17]

I have changed the the base valves with Gold Valves, the cartride valves have been rebuilt (bushing, seal and shim each) and the mid-va;ve has been converted to check plate style as per Gold Valves instructions. The stiffer shim stack is at the bottom of the mid-valve and the check plate is on the top (I hope that is the way it's supposed to go). If I remember correctly, the check plate on the base valve faces upwards

The way I read this it seems that you might have the check plate rebound reversed. The rebound stack will go on top were the nut threads on to the rebound post. the compression or check plate will go toward the bottom of the rebound post. The mid is not like the base valve in regards to the check plate placement.

Russ

 

[Quantumcanuck]

lol... I'm getting confused. The end of the rod where the mid-valve is located points downward. So I say that the multiple shim stack is at the bottom of the valve and rod (the nut side) and the check plate is at the top of the valve (facing upwards).

Is this correct?

John

 

[russ17]

Correct

Rebound stack is on the nut side

 

[KTM-Lew]

Ok....glad you didn't take my post wrong! Maybe your mid-valve conversion is the problem? Can you post some pics online of the rod/rebound piston assembly?

 

[Quantumcanuck]

I wish I could but the digi-cam is on the bum.

Thing is, I have been having this problem since after I got it 2 years ago. Changing to the gold valves and making the mid-valve check plate style has made a diffrence. A good difference? I'm not sure, it's just different feeling.

I just pulled a leg apart and when I had the cv tube out with the base valve removed, I pulled up on the rod to get any remaining oil out from above the mid-valve. As I did this a shower/spattering of oil came flying out the bottom. Thing is, I had little resistance pulling the tube up leading me to beleive the oil was just blowing by the piston band and not actually passing through the shim stack.

I'm going to order some piston bands for an '02 KX250 and put them on. I think they are the open type that get wrapped around and lock together at the ends (like a piston ring). I picture that type of band always sealing up against the innner cv tube walls no matter what.

 

[KTM-Lew]

Ok? You are convinced that is the problem.....guess it won't hurt to try it! Good Luck!

 

[KTM-Lew]

So this problem existed from new?

 

[Quantumcanuck]

No, I distinctly remember a very noticable difference when a friend told me the front was too stiff (I was a total newbie, first dirtbike). He proceded to turn the top clickers out, how much I can't remeber. I went for a ride and all of a sudden the front end felt springy. So, this memory is leading me to think that I should feel (even see) a noticable difference in rebound from full in to full out. I don't, nothing changes. And nothing changes on compression either; full in to full out makes no difference.

So in my mind oil is getting by too easily some place negating the damping shim stacks and adjuster effect. The base valve is brand new so that can't be it. The cartridge valve has all new parts in it so that can't be it.

What else is there that would make my front end have so little damping and no control over it either?

Thanks guys

John

 

[russ17]

Push down on your rebound rod to see if the reb needle is moving freely. You should be able to push it down with your finger and it should return. also the little o-ring on the needle might or could be damaged. Just suggestions to look at
It would be nice to post some pics.

 

[Quantumcanuck]

I have tested both compression and rebound needle circuits with forced air. Full in doesn't let any air pass through and full out lets it all go through. The rebound needle springs and o-rings are in good shape. The rod is loaded and is pushed back after I depress it with my thumb.

I'll work on getting pics.

JOhn

 

[Quantumcanuck]

I looked on the forum for posts but there doesn't seem to be anyway to add pics to my posts. Is this the case here?

I have made pics. Where can I put them so all can see and help?

Thanks :)

John

 

[Quantumcanuck]

OK, I found this putfile site. Here are all the pics I made with my cam. They are not crystal clear but I think they are good enough. Anything else you guys want to see just say the word and it's done.

Thanks :)

John

http://putfile.com/pic.php?pic=10/27607585863.jpg&s=x1
http://putfile.com/pic.php?pic=10/27608032033.jpg&s=x1
http://putfile.com/pic.php?pic=10/27608040392.jpg&s=x1
http://putfile.com/pic.php?pic=10/27608042562.jpg&s=x1
http://putfile.com/pic.php?pic=10/27608044173.jpg&s=x1
http://putfile.com/pic.php?pic=10/27608051966.jpg&s=x1
http://putfile.com/pic.php?pic=10/27608053997.jpg&s=x1

This last pic is of the cartridge valve shim. I'm just showing that it is flat and in good shape.

Also how many people are familiar with the piston band that I have? It's solid as a rock and doesn't have a break in it. It's nothing like the ones I see advertised on certain web sites.

 

[Quantumcanuck]

Is there anything wrong with the valves from what can be seen in the pics?