mid-valves are my problem?

[KTM-Lew]

Nothing jumps out at me? Strange deal! Are you certain you have the rebound needles inserted in the correct direction? Does the cap bottom on the rod so the adjuster actually works?

???????????? :uh: :think:

 

[Quantumcanuck]

yup, the cap bottoms out on the threads of the damper rod then I tighten the nut up to it. The adjuster has the 19 or so clicks that it's supposed to as well.

Does anyone know where I can get some mid-valves for this bike? I'm sure it's the band around them, I can't see anything else causing the problem.

 

[soulmate33]

I read a post here from someone who installed gold valves on his bike. Initially he converted the mid valve and said that the bike blows thru the stroke too easily. He ended up putting the mid valve back which made a big difference.
Do a search on it: gold valve, mid valve, etc.

 

[Quantumcanuck]

yeah, I could see how adding the compression stack back on the mid-vale would drastically increase compression damping but it'll do nothing for my rebound, which I have no control over.

I can't believe all the trouble I am having just trying to get a mid-valve piston band. I'm so tired of the bike, its no fun to ride at all because it's a nightmare to man handle all the time. The front end is retarded. I've been trying the entire summer to get this problem sorted and I can't. I'm tired of spending money on it to get fixed and nothing fixes it. I could have bought a pair of good used forks from **** at this point :(

It's not the compression valve and it's not the cartridge valve... what else could it be????

 

[marcusgunby]

You seem to be going around in circles, you sure mx tech or others like race tech dont sell the piston rings?? also try 7.5wt oil, it maybe all you need?? it seems you are thinking too much and doing little.

 

[Quantumcanuck]

Well, I have had the cartridge valves rebuilt, the forks rebuilt and have replaced the compression stacks with Gold Valve set ups... how is that doing too little?

Anyway... I believed from the begining that it was the seals around the pistons, for many reasons, so I will try to replace them with something. If there is nothing I can find then I will get rid of the bike. It aint worth all this hassle.

Thanks

John

 

[marcusgunby]

john sorry to sound harsh, its just i think you have got a issue with the piston rings, and until you try something we wont know for sure, i know a set i have valved recently are way soft for the setting they have, so i think the forks vary from bike to bike, the 7.5wt oil would make a difference if you have bad tolerances and make it act like a normal fork, you could try one leg in the garage with 7.5wt and feel if its different to the one with 5wt?

 

[Pete Payne]

Have you tried resizing the mid-valve piston ring ???? You can do this , once your fork is disassembled , cleaned and dry,by heating up the cartrige tube for a minute . Put the mid-valve at the toped out position , heat up the middle of the damper tube(all the way around ) with a propane torch for a minute then push the mid valve piston past the hot spot a few times and let it cool .

 

[Quantumcanuck]

I have tried heavier oil weights all summer. they help a little but come far from solving the real issue. The effects of the shim stacks and damping circuits are being negated and in order to get the proper damping curves I need to get the whole system working properly. I agree with you that it seems oil is blowing by the piston bands. In fact, i'm very sure it is.

J

 

[Quantumcanuck]

Have you tried resizing the mid-valve piston ring ???? You can do this , once your fork is disassembled , cleaned and dry,by heating up the cartrige tube for a minute . Put the mid-valve at the toped out position , heat up the middle of the damper tube(all the way around ) with a propane torch for a minute then push the mid valve piston past the hot spot a few times and let it cool .

Wow, this seems to be a revelation. How did you come to know this?

So heat will cause the piston band material to expand and take the shape of the cartridge tube?

How much heat? Not red hot I suspect.
Will I feel the band expanding as I move it past the hot spot?

Whatever else you can tell me about the process i'd really appreciate it.

John

 

[steve125]

The Chunk knows suspension! Thats pretty much a 1/2 of what he does all day. ;)

 

[Quantumcanuck]

Oh, I'm sure he does. Just that one post has made me see that he knows his stuff. I just want to clarify the process before I botch things by doing them wrong. I'd also like to know if that's what they do in the factory to size the bands in the first place, or something like it.

I'm very excited that he used the word resize and not reseal. It's not the mating surface I am having problems with, it's the size of the band. I'm sure it's letting way too much oil fly right past it negating the needle circuits all together and rendering them useless.

I'd also like to know if he has seen this happen before.??? :)

Thanks

John

 

[Pete Payne]

I have had to do this on older units . It seems to be also a wear issue of the I.D. od the cartridge tube . I have seen it slow down the rebound noticably , due to better sealing. I would only use a propane torch and heat it for about 1 minute all the way around the tube. Then pass the piston past the hot spot a few times , back and forth , and let it cool .

Sometimes you can tell if the I.D. of the cartridge tube is worn out if you push the piston through the tube and pull it and you have a noticably different amount of drag in sections of the stroke.

Also as Marcus noted you can make a new piston band out of a shock piston ring and cut it to size , Normaly the shock piston ring is thicker and will help sealingin the worn area.

 

[Pete Payne]

One other thing you could do is to set the tube up in a set of V-Blocks with a dial indicator and see if there is a slight bend in them or if they got a pinched area from being chucked up in a vise.

 

[Quantumcanuck]

Perfect :) Now I don't feel so discouraged with this bike.

I did the heat method last night. It seems to have decreased the amount of side to side play I see when the mid-valve is as far as it goes into the cartridge tube and from the bottom I use a small screw driver to wobble it from side to side. We'll see this weekend if it has made a difference and I'll keep you guys posted.

I don't think there is any wear of the cartridge tube i.d. It feels pretty consistant from top to bottom.

I really like Marcus' suggestion of gettting some shock piston bands and cutting them to fit. I would just have to make sure they are the same height from top to bottom and the length I could tailor to the mid-valve diameter myself. I just measured it and it is exactly 5mm in height. I will start to call around and see what I can find.

Alright, I'm off. I will keep you guys posted.

Thanks

John

 

[Quantumcanuck]

I broke down tonight. I took a brand new exacto blade and very carefully cut up 2.5mm, then over 6mm, then up the last 2.5mm. Now the piston band can expand to the proper size to seat itself. I reassembled and checked the rebound from full out to full in. Major difference. There is actually damping now and I actually have control over it.

My only concern is that without an o-ring underneath the piston band, it is not sealing as well as it could. Maybe under high oil pressure/flow situations the band could just get pushed back off the cartridge tube wall and let oil by. Maybe just a little or maybe a lot, beats me but it would certainly lead to inconsistant damping.

There is no groove machined in the mid-valve to accept an o-ring. I'll have to find some other way to keep the piston band forced outwards. There isn't room under there for much though.

Atleast I know for certain that what I thought it was all this time is actually the problem.

Supposed to rain this weekend :( Hopefully I'll be able to gt out and do some testing.

Cheers and thanks for the help guys.

John

 

[Pete Payne]

On the WP's mid - valve piston the piston band has a stepped cut in it and there is no oring underneath the band either. I suppose I could machine a groove in the piston to accept an oring.

 

[Quantumcanuck]

Hmm..... well if it's good enough for WP then it should be fine for me :) I'll see how things go this weekend. I'm just relieved to have made progress with the help of you guys and this board.

J

 

[Quantumcanuck]

Because of the rain i was only able to hit the local sand pit around here. There is a rather large jump in there and I was purposely coming up short in an effort to make it bottom out. I wasn't able to do it even though the front is soft feeling so I guess cutting my piston bands to allow them to expand a little was a good idea. there is now also a noticable amount of rebound damping as well.

However the bike feel kind of wallowy when i am going over bumps fast and corning a little at the same time. The bike seems to get loose on me. what is tis a sign of?

Thanks

J

 

[marcusgunby]

Sounds like you just may need a few more clicks of compression, sometime 3 more clicks can make it perfect.Maybe try a tad more rebound as well maybe one click.

 

[Quantumcanuck]

yeah, even though I was having a hard time getting it to bottom it still felt too soft everywhere esle.... hopefully I can make the track thursday and do some testing.

J

 

[Quantumcanuck]

I'm still having issues with the mid-valve piston band. I can't get them seperately without dropping 1000 for 2 cartridge assy's and that's not gonna happen. I have tried the key type piston band and it has definately helped but because there are no o-rings underneat oil is still getting by.

Does anyone know what years KYB use the same diameter mid-valve assys? I'm going to just oreder some and put them in my forks and get rid of that wierd one peice piston band style.

Anyone?

Thanks