YZF Suspension Midvalve??



80 replies to this topic
  • DaveJ

Posted November 05, 2001 - 10:12 PM

#21

Motoman,

Well, I know what that over-the-bar feeling is like.

So what sort of work did they do on your collar bone?

Any surgery, or did they just set it?

DaveJ

  • Scott_F

Posted November 05, 2001 - 10:41 PM

#22

Garrett, I'm about the same size and weight as you. The furthest I jumped my 426 was about 120'. I overjumped, flat landed and didn't get hurt. It is for these situations that I highly recommend the bottoming cones vs the bumpers. I strongly believe that they improve the last two inches of travel.

I recommend you run bottoming cones, 90-100mm oil height, stock springs, stock midvalve and base valving first. Then modify those stacks to learn the effect. After you have gone as far as you can with that, then try gold valves.

You say you want to learn all about suspension tuning, and changing one thing at a time is the best way to learn. One of the best things you can do is to watch a local suspension guru tear them all the way down and reassemble. You will learn A LOT before attempting it with no previous experience. If not, then get a video. Also, you will need to buy some tools to do the work properly.

I agree with everything John Curea said in his first post. It was very well stated. He is also right about a total teardown to check for wear and damage. But I do disagree with lighter springs. My God man, you are jumping 140'!!! You do not need softer suspension.

  • John_Curea

Posted November 05, 2001 - 12:49 PM

#23

DaveJ

The only problem with installing bottoming cones is that you will be increasing damping in the worst area- the high speed circuit. You have to understand that the cylinder valve (what you call seal head) has a shim stack inside that is very linear in design. It doesnt flow oil until you have a high speed hit, then it blows off, softening the hit.
When you replace this cylinder valve with a bottoming cone (which does not have a high speed circuit)you increase the high speed damping (spelled harsh)because you just removed the high speed damping of the CV. In order for the bottoming cones to work well YOU MUST soften up the high speed circuit on the base valve to compensate. They are not just a direct replacement for the cylinder valve, there is much more to it.

Yamaha has actually changed the high speed circuit in the '01 426 cylinder valve, can you guess which direction they went?

Dont get me wrong, bottoming cones work really well in certain circumstances, BIG hits , missed timed jumps, flat landings etc. . 90% of the time the elastometer(bottoming bumpers)works much better. On a slow speed bottom, bottoming cones offer almost no resistence(spelled damping). The shaft speed has to be pretty fast in order for them to work. If you think about it, if the shaft speed is too slow through the bottoming cone, it will easily displace the oil in the lock providing little or no damping.

The main office of MX-TECH has done alot of research with the engineers at Mobil before they ever tried this fluid. We blend this with a velacite product to lower the overall weight a little. But as we stated somewhere else on TT that fluid viscosity directly affects LOW speed performance, the additional low speed damping that this fluid produces(which would actually be a plus in motomans huge air jumps)can be tuned out with the clickers. The clickers as we all know primarily affect low speed performance.
No reason to contact KYB on this matter, we already have a huge amount of testing with positive results and very satisfied customers.....

As far as the headshake goes, we basically have two types, gas off deceleration headshake and gas on high speed head shake. When motoman is blazing at 65mph and his front end starts shaking it is usually because the front end is too stiff. When the front tend is too stiff it is easier for the front end to displace the rotaional mass of the spinning front wheel to the side than it is for the suspension to absorb the hit. This is a direct result from him using too stiff springs for his weight.

Just for thought- Decelleration headshake is usually because the front end is too soft and the front goes too far into the stroke, sigificantly tightening up the bikes geometry.

As far as spring rates, going to the factory teams might just suprise you. Pastrana was running a progressive fork spring starting at a .34 rate !! If I put that in a customers bike, he would probably launch it right back at me !!
The factory riders have some pretty wild set ups, have you ever noticed how soft RCs shock is, it seems to flatten out on the smallest stuff on the course. His forks are rumored to be very stiff. I dont really see how taking those spring rates and applying them to the average rider would do any good.
I think you might have gotten motomans weight (168#) mixed up with someone else posting on this thread, there have been a few different readers posting there weight.
Even if motoman was running pro level SX, I wouldnt put him on anything stiffer than a 4.6 in the fork.


I hope this helps
John

  • motoman393

Posted November 05, 2001 - 12:52 PM

#24

Man I appreciate all the replies on this topic guys...and this info really helps alot! But it seems everyone has their preference/opinion on the midvalve removal and the installation of the gold valves (The same thing is true for people who prefer richer/leaner jetting, or preference of regular/synthetic oil)!

I like what Scott F said (and he makes a good point)

I recommend you run bottoming cones, 90-100mm oil height, stock springs, stock midvalve and base valving first. Then modify those stacks to learn the effect. After you have gone as far as you can with that, then try gold valves.

I think I should stick with the stock valves/stack until I learn what the shims do etc on the handling and characteristics of my bike! Then if I am not quite pleased with the results I can goto the gold valves (makes sense financially to change what I have now instead of spending $160 for gold valves).

Scott F,
Do the bottoming cones go in place of the blue bumper at the top of the fork? or at the bottom of the fork? I always get a loud "clunk" whenever I land real hard or come up a tad short on a jump...I'm assuming the bottoming cones help aid this right (hints the name bottoming cone duhh?) What bottoming cones would you (or anyone) recommend? And what is a good price for a pair of them? And Im sure the installation is not challenging right?

BTW I have completely taken apart forks a few times...including the internals for proper cleaning (I did this after I broke my bike in) but I never messed with any of the shims/valving, etc. (so I am not by any means a expert at suspension...but I understand the basics of how it works) I am going to do all the suspension work myself so feel free to give my any suggestions or "tricks of the trade"! I already have a seal driver, damper rod holder, and an air impact wrench (and all the normal tools) and these have worked on all my previous fork seal jobs. What other "special" tools do I need to buy?

You also mentioned about changing the valve stack on the stock unit. What is you current valve stack set up? In order to change the stack do you have to buy new shims or do you just move the existing ones around (I havent looked closely at the stack before so I dont know exactly how it works, so please excuse my lack of knowledge) It is amazing how much I have learned just by reading on this forum (and dirtrider.net's suspension forum) the last 3 days. I really appreciate all the help! Thanks,

Garrett

  • DaveJ

Posted November 05, 2001 - 01:35 PM

#25

John,

The problem with the factory seal heads, (aka cylinder valves) is that they fail. Worst case, one fails and the other keeps working. Since they are not serviceable, there's nothing you can do.

Since they fail at various degrees, dialing the suspension via the low and high-speed stacks for the two forks is nearly impossible.

So yes, I agree that it is required that the high-speed circuit be modified, but at least you get an environment that offers tuning consistencies.

As for the application of bottoming cones, you'll need to take a few hard hits before you realize the benefits of these over the stock bumpers.

The bottoming cones also offer less response snap or bounce back after a hard hit, which keep the body from launching into or over the bike. You may want to test a set out and see what they feel like.

As for headshake, I think we may need to understand the difference between what starts it, what keeps it going, and what stops it. Normal bar movement (like a bar smack) will increase with stiffer forks, but this is very different than then oscillation that he is speaking of. If the bike is not able to cancel itself out, it usually means that there’s a forward weight shift (usually corrected by increasing rear sag) or the forks themselves or not consistent. Aka, one fork is working harder than the other. That comes from years of tuning on the road circuit; so if I’m missing something as we convert to dirt, let me know.

As for spring weights, I'm not sure where you get these numbers for this style of riding unless you're really putting the load on the hydrualics of the forks.

As for Pastrana using a .34 progressive spring, that's not a fair comparison since this is the initial weight of initial movement. You'll have to inform us what the concluding weight is before that becomes a valid point.

Lastly, you'll need to let us know why you guys are so adamant about using the ATF stuff. Is this a cost reduction issue or did you find that the properties of ATF were better than off the shelf fork oils? (I'm not bashing you, it's a serious question...and I'm really curious).

I've tried a lot of oils and have yet to find anything exceeding the KYB oils distributed via Enzo.

Thoughts?

DaveJ

  • MX_Tuner

Posted November 05, 2001 - 03:01 PM

#26

I think you'll find with John the only right way is his way.

  • DaveJ

Posted November 05, 2001 - 03:26 PM

#27

MX Tuner - That's kind of harsh.

I'm sure he's open to discussing this case a little further. There's always something to learn.

  • John_Curea

Posted November 05, 2001 - 03:46 PM

#28

Hey Tuner
You make me sound like the "its my way or the highway guy" !!! LOL

Nothing could be further from the truth, I absolutely love working on and discussing suspension. I got so wrapped up in suspension work that I left USairways after 12 years as a Jet Engine mechanic to pursue my dream.
I was just trying for you to substantiate your claims (more so than just saying midvalves "suck"). I love a good debate, and suspension is a great topic. If you or any one can generate a good arguement against what I am saying, by all means go ahead. I am very open minded.
I have a whole different reply that I am starting on another browser, I tell you guys, I love this stuff.....LOL

This thread has consumed the better part of my day, you gotta love it.

John (wayne) LOL!!

  • John_Curea

Posted November 05, 2001 - 04:55 PM

#29

Dave
Why do cylinder valves fail? Is it from distorted shims or contamination ?have you ever had one apart?
They are rebuildable, very carefully remove the shoulder, an easy job on a lathe. The ones that I have seen that failed , did so because of contamination. Once apart, an easy clean job, upon re-assembly just make sure sure you provide enough preload on the shim stack to make it work but you dont want too much or the CV will not sit properly on the shoulder of the cartridge.
More and more, suspension work is moving away from the average mechanic with a set of hand tools. Have you ever worked on a PDS, I tell you these things scare most suspension tuners. They are actually a thing of beauty, but the bleed pump WP reccomends to service them cost 1500.00 !!

You go on to state that if one CV fails it throws the fork out of balance. Have you ever seen a 'Zoke? where one leg handles all of the compression and the other all the rebound ??!!And they have a wimpy little axle connecting them. They work just fine offroad. I think your road race mentallity is cool, but it doesnt really apply offroad.
In a road race enviroment, you even have to factor in the side load on the front end when you have the brake rotor on one side only during heavy breaking, and these bikes have big beefy axles.

On the topic of Motoman needing heavy springs to handle the big jumps, if we were tuning for big jumps only, I would agree, but what about 90% of the rest of the track? How many times have you heard "The race is won and lost in the turns", if we valve and spring for big jumps, what happens to Motoman everywhere else? he would suffer in the turns. Alot of times we look at little bits of information and forget to look at the big picture.

If you look at the top ten riders in the country, they are catching huge air and railing turns you say?? Yes, but they are timing thier jumps perfectly, and when they dont.....look out.

I see where you are going with your headshake reply, but again I think that more applies to a road race enviroment.

As far as Mobil 1 ATF, it rocks....cost effective, hardly..especially when you look at how we blend it and have to stock other fluids. On the performance side, all I can say is too be open minded and give it a try, if you want I will send you some Dave.
We went on before about the slightly heavier fluid increasing low speed performance. As we stated elsewhere, a shimstack and piston are nothing more than a variable metering orifice. Oil viscosity has less affect with a larger port opening (as in a highspeed hit) and more so with a small opening (as in a low speed). This is why a slightly heavier fluid will improve low speed performance and make the clickers more adjustable. Because as we know clickers affect primarily low speeds.

I hope this helps
John

  • Drehwurm

Posted November 05, 2001 - 10:43 PM

#30

Servus John,

Have you ever seen a 'Zoke? where one leg handles all of the compression and the other all the rebound ??!!


I might be wrong, but I was of the oppinion that both legs of the Marzocci's featured comp AND reb damping, only adjustability was limited to either leg. Apart from that, I think that your point is valid.


motoman393:

For what it is worth, I had a 98 WRz400 with Gold Valves (midvalves removed) which I loved for its plushness. Now I have a KTM520EXC with a MX-Tech setup where I mainly concentrate on working with the midvalves, and again I'm very satisfied with it. The point? If you want to do it right, have your suspension setup by someone you trust and use this as a starting point for your own experiments. You'll save a lot of time and hassles, believe me! I can recommend both, MX-Tech and Race Tech.

BTW, 4 weeks ago I broke both my collarbones on a bike where I'm very satisfied with the suspension - nothing can save you from rider error :)

Michael

[ November 06, 2001: Message edited by: Drehwurm ]

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  • MX_Tuner

Posted November 06, 2001 - 01:59 AM

#31

Not trying to be harsh but it seems obvious John is of the mindset that only his way will work well. Discussion is good. Trying to beat it into everyone that your way is the only way ain't a discussion.

And look back at what I wrote about the midvalves. I didn't say they sucked. I said "I" thought they sucked. I've had much better luck disabling them. Why put words in my mouth? Everything I post here are personal experiences. That's all. Just like with you.

[ November 06, 2001: Message edited by: MX Tuner ]

  • DaveJ

Posted November 06, 2001 - 08:08 AM

#32

John,

So yes, I have rebuilt the cylinder valves before, but what a pain in the butt when you want or need to rebuild these things on a regular basis. And you're right, most YZ owners don't have the tools now required.

Besides, I like the tuning and service simplicity of the bottoming cones, and of course, the bottoming effects. At least try a bike with them and see what you think.

And I agree on your theory that the race in won in the corners, but still, that's a very soft spring. Perhaps the progressive approach offers the best of both worlds.

And thanks for the offer on the ATF, but I'll stick with the KYB juice. I've grown partial to it.

I'm sure in the advanced arena there is not a single rider with the same fork set up.

Good to learn from others.

Thanks again for all the great posts.

DaveJ

  • DaveJ

Posted November 06, 2001 - 08:49 AM

#33

Motoman,

I'll sum up my opinion, and perhaps others can do the same. From there you can decide and experiment with each approach.

Modifications to the valve stack - I think for everyone, this should be on the list of things you should be able to do. It's relatively easy and can be done with little effort once you get the hang of it. Understand the configuration of a two-stage stack, note what you had and what you changed to. Gather up the stacks of what others are using and the style of riding they do. This is truly the one thing that can make a big difference. Besides, quick mods can be made with little disassembly to the fork.

Springs - My thoughts are to go with a minimum of .47. This is what I run and I'm the same weight as you. I feel this is also warranted for the corners as well, especially if you are moving at high speed. However, a progressive spring may be worth a try. For the rear, I run a 5.6 at a sag of 100mm. However, keep notes on preload and sag settings both front and rear. This based on my theory that a bike should be suspended around its center of gravity. In other words, the front and rear should average out to work nearly equal.

Mid-Valve - For SuperCross use, keep it in. However, if you want to keep the fork finely tuned, you may have to flip or replace its shim stack on a regular basis. I think I have found that they fatigue over time with heavy usage. At least be aware of this. For trail riders that are dealing with the pain of high compression movements into the hands and arms, pull this out, but not without replacing the factory seal head.

Bottoming cones - in my opinion, it's a must have. As mentioned, these offer outstanding hit performance, and will even aid with keeping you on the bike during the rebound cycle. Not to say this would have saved you, but it may have helped. I also like the fact that they don't use a shim stack in them, making the fine-tuning of the bottom valve stack easier. Takes some work to put them in, so plan accordingly.

Ultra-adjusters - if I was racing pro, I would not use these. But for quick changes for those of us that do trail and track, they are worth it. They offer both external low and high-speed compression settings. They work very well, but many complain that fine-tuning can only be done with stack changes. Keep in mind, that you still have to vary stack changes to get something close to what you want, but at least you can vary the ride with a screwdriver. I use C-Cycle and they provide a stack sheet to use with their adjusters, for all levels of riding. Requires a 30mm socket (or was it 27mm) to install and remove.

Fluid - I can't go with the ATF for a collection of reasons, but it sounds like it really works for many. Of all the brands I have tried, the KYB O1 via Enzo Racing is the best. I would have to assume that if use a thicker oil, the stack would have to be adjusted accordingly. Keep this in mind if you change oil types mid stream.

Fluid level – this one it up to you. Try different settings. With the bottom cones, I run 100 to 120mm.

Fork coatings - I experimented with titanium nitride on my road bikes and had great success. The biggest concern is finding a shop that is good enough to do large parts. I have also done this on the dirt bike, and have been very pleased with the results of low speed friction reduction and seal longevity; however, I have heard that titanium nitride can effect the metallurgical values of the metal. Seldom do I see this done any more in the off road circuits so perhaps this is why.

Other mods - Many in the past spoke of polishing the compression rods for a smoother operation. On this particular bike, the rod has a coating that is rather soft. If you have to polish any imperfections in it, do so with a very fine cloth. If the metal can be seen, the rod needs to be recoated or replaced, (and the seal head bushing as well). However, polishing of the fork tube is recommended. Always make sure to remove any water spots after washing.

Lastly, always run Loctite on the valve stack assembly and rebound assembly. And seal all drilled holes in the cartridge tube if you install the bottoming cones. If not, they leak.

Again, take notes, pay attention to the details, and work meticulously.

Hope this helps.

DaveJ

  • John_Curea

Posted November 06, 2001 - 05:31 PM

#34

"Again, take notes, pay attention to the details, and work meticulously."

Excellent advise, from the work that I have seen around the industry, if you do good quality work (leave no sharp edges, no plier gouges or ,god forbid, vise grips), you will be 80% ahead of most of the work being done.

This has been an excellent thread, I have enjoyed it, good replys from ALL.

Take Care, John

  • Scott_F

Posted November 07, 2001 - 12:28 PM

#35

For the most part, DaveJ and I are on the same page. Dave, I found that when drilling out the seal head dimples, if you use a small drill bit, like around .125", leakage is not a problem.

When it comes to low and high speed impacts, we all have our opinions. Here's another: Some jumps landings are low speed events and some are high speed events. A low speed landing is one where your touchdown perfectly matches the landing slope, and you get that cloud nine pillow soft feeling. Is anything better? Then there is the high speed impact landing, such as landing short on a double or tabletop, or overjumping and flat landing. These mistakes cause the suspension to collapse at a very high rate of speed, often leading to harsh bottoming.

For those who go big (or are big), and are not perfect, the bottoming cones can save your wrists or even prevent crashes and injuries. If they do prevent some HS damping under those circumstances, then that's a good thing. The cones have to be tried to be believed, and I believe most works forks still use them. Dave, did you know you can buy slightly oversized bottoming pistons for stock cones on non-bumper forks?

  • DaveJ

Posted November 07, 2001 - 02:08 PM

#36

ScottF- I've been wondering where you were.

Replacements for stock pistons? Do you mean the ones you cut to remove on the compression rods? If this is the case, I would assume oversize means longer.

As for leakage out of the compression tubes, on my....ummm...second set, I drilled with a smaller drill and never went through the metal, therefore never making contact with the factory seal head.

Months and many rides later, I found that some of the holes where blown out. Perhaps I still removed too much metal or need to run my Locktite a bit lower. Must of been one of those high-compression landings. Some of the holes were very small, so do check this on your next tear down and let me know if I'm still drilling too deep.

And now that I have your attention, are you toying with something red in your garage these days?

DaveJ

  • John_Curea

Posted November 07, 2001 - 07:59 PM

#37

Scott, Dave
On the topic of removing the cylinder valve. Relieve the peens with a 6mm end mill, go 1.35mm deep. A set up in a lower end drill press with a vise will work just fine. 1.35mm deep removes just enough material, without going into the threads in the cartridge.
Add heat with a propane torch to melt the loc-tite. You can make a device from hard wood to hold the CV. Remove the metal spring seat first, to get the pattern.
If you happen to trash the threads, use a replacement '96 honda cartridge assembly (about 87.00 retail from honda)it is way cheaper than buying directly from yamaha. Although the '01 CV is valved alittle differently.......no big deal if you are installing the bottoming cones.

Good Luck , John

[ November 08, 2001: Message edited by: John Curea ]

  • John_Curea

Posted November 08, 2001 - 03:55 AM

#38

Dave
I beleive what Scott is referring to about the oversized pistons is the O.D. of the piston. We use a larger (OD) bottoming piston in the Showa applications, provides more resistence to bottoming.

John

  • Scott_F

Posted November 09, 2001 - 10:26 PM

#39

Right John, for Showa and Kawasaki KYB.

As for the peens, I drill a small hole clean through the cartridge tube into the cylinder valve/seal head. I don't care since I won't be reusing it. Then I loosen the locktite with a heat gun and a dead blow hammer. I lay it down on an anvil and firmly tap it around the circumference. This does not hurt the tube since it is kept round by the head. If the holes are small, they do not leak because they are covered by the bottoming cone threads.

  • motoman393

Posted November 13, 2001 - 02:21 PM

#40

Hey guys,

One more quick question...

While I am taking my forks apart I am going to go ahead and replace the fork seals (I bought them today from my local Yamaha stealer...I mean dealer LOL). They are not worn out or leaking but they are 1 yr old, and since I am taking the forks apart, I think I should replace them! I have heard of people shortening the springs by 3 mm around the dust seal and oil seal (to make it seal better, thus reducing leakage) Does this increase stiction, or prolong the life of your seals? What do you recommend? I take very good care of my seals, I lube/and clean them after every ride (this is why they still are good after 1 yr of hard riding)!

Also the shock takes US-1 5 wt oil...but approx how much oil does it take? I bought 2 qts, will this be enough for both the front forks and rear shock (for a complete disassembly)? Thanks for your feedback! Later,

Garrett





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