Cylinder Valves

[PMK]

Terry
Yes this is the type of setup I was refering to, a ball, seat, spring check valve for partial cartridge filling during compression. The setup could be positioned in place of the cylinder valve but obviously not in the cup area of the bottoming control device. The small jet would also allow some filling but as JW stated emulsified oil will flow more quickly than solid fluid, therefore the jet would tend to try and bleed off any cavitation emulsified fluid trapped between the upper catridge gland and the midvalve / rebound pistion assembly. This could also allow tuning via tension, ball mass, diameter, and quantity of jets and check balls. Also with reciprocating movement and moderate flow, contamination would be reduced at the seat.

In further persuing the piston port area issue and the terminal fluid velocities. Do you have the data on fork compression velocities that you would like to share?

It's possible that JW is correct in that orifice area is not a limiting factor, and since many pistons are cast and machined so that the point of pressure is not round as in a drilled hole, the pressure is placed across the entire area of the port edge, thereby changing the contact point and fluid pressure centerline.

The issue still remains though that if cavitation exists on the rebound and the check plate cannot fill without emulsifification of the fluid the midvalve will still be driven thru emulsified fluid on the next impact, however by purging the cartridge at the upper end at least there is some form of venting and recirculating the fluid. This can also hold true in regards to the base valve and refilling thru the lower checkplate, but again it can at least have a flow path.

PK

 

[Jeremy Wilkey]

Originally posted by PMK


It's possible that JW is correct in that orifice area is not a limiting factor, and since many pistons are cast and machined so that the point of pressure is not round as in a drilled hole, the pressure is placed across the entire area of the port edge, thereby changing the contact point and fluid pressure centerline.
PK

Yes that's the case exactly.. If you look at the Honda CBR fork pistons this is not what they are doing and Terry's point is valid... But that has more to do with the fact that want a steep damping force line with a very shallow tail. The shims offer very little control of area, only a very stiff characteristics followed by almost unlimited area.. Good for road race by some intentions..

Ohlins was going for a version of this plus what I was speaking too earlier. With there newer generation stuff.. What's interesting as even with such small holes we are not to Velocity X valving yet..

In other words as you pointed out, I use orifices with a port, the port controls low to mid area relationship, and the "jet" produces enough force to create excess deflection, and accelerated area growth for less high speed. Ohlins is doing the same thing.. Only to a more radical end..

It amazes me how many potential twists we have in this equation, finding the limits is a long and tedious process..

Great topic..

BR,
Jer

I'll be out doing some riding and PR in AZ with John Lakivich.. Looking forward to what happens till I get back..

 

[PMK]

JW
As you've stated unless I misinterpeted, you are using delta P for low to mid deflections and an impacting flow to assist in bending the shims for higher flow rates. If this is true then the best way for orifice area is derived fom stroke velocity with a calculated fluid flow from the cartridge. This will provide the minimum size to prevent a regulated flow thru the orifice and then this value needs to be increased by a given percentage. No?

So back now to Terry or even JW. Have you folks evaluated and compiled fork velocity data? And if you did was it compiled using soft valving to allow a huge blow thru of travel as this would provide an extreme to base from?

PK

 

[terry hay]

PWK
We could well calculate this whole thing mathmatically. Fork travel could be measured in metres per second (distance over time). The cross sectional area of the damper rod would provide a means for calculating displacement. We would need an accurate port area measurement. Then we could calculate fluid velocity using a simple nozzle discharge formula. Other factors also come into play. Fluid bypass from the cartridge etc. And this is where it gets difficult.
Some factors we should also keep in mind regarding fluid dynamics. when pressure is applied to a fluid, that pressure is equal and undiminished in all directions. So pressure is applied to all areas of the cartridge, valve ports, shims, bushing clearences etc. Any size orifice affects fluid flow. In other words a trickle of water flowing through a 3 foot pipe is still influenced by its dimensions. So yes any port dimension will have an effect on fluid flow (damping). Any orifice will also create a loss due to friction. Remember back to our old damper rod forks when we relied specifically on orifice dimension to provide all our damping. Granted the fluid flow was greater but the holes weren't exactly small. How much influence is generated I guess is the question that begs to be answered. And if it can't be answered it should at least not be ignored. Unfortunately when we start disecting this far we begin to get into the "splitting hairs" area and tangents become all to common. If you wish I can supply you fork velocities from data collected from our testing with Craig Andersons CRF450 at the White Bros. SX track and a discharge formula which will provide hours of entertainment.
Regards
Terry

 

[PMK]

Ahh but Terry, a base line needs to be first setup or how would anyone wild card guess and know they haven't created a flow restriction in the orifice itself. Granted there are bypass losses that would be difficult to calculate and as you stated all orifices will create some type of dynamic friction. But if the velocity is known, in a value that can be calculated, (cm/sec or other), and most would need to assume for calculations, that the leakage is zero, it would then put an end to the smaller orifice is restricting the flow resulting in a damping spike. This is one area that many folks feel they need pistons with huge ports, no one has ever come forward to say you should have this much orifce area, after that it's almost like porting a cylinder, there is a lot of things that work, some that don't, and everyone is promoting what they offer. (This is in general and not attacking you or anyone, you need to beleive in what you do). The entire orifice size issue is not unlike people buying a free flowing exhaust for the car, just sometimes you can put pipes on so big it goes pop, pop, pop instead of vrroom.

In regards to a damping "stick" fork, the method was easy and when done reasonably they would ride well for the terrain that was being ridden. When one understands that these were basically an entirely stepped free bleed system, the thing was critical of orifice area and placement. As said these relied heavily on orifice restriction and internal leakage. And some of these forks work very well today for the average rider. (mx not sx)

No I don't need to be entertained with data. I just would almost like it laid to rest about the large orifice / small orifice issue, especially if the present oem forks don't realy have a flow restriction problem. As it stands, it's the port shape and oil jetting impact velocity combined with the obvious stack makeup that get your end results, and if you test and offer one setup, and someone else offers another and both arrive at the proper end result, I suspect most folks wouldn't know how it worked just that it's better. Besides I'm sure many if not everyone that's decided to valve on there own to their own specs knows how bad it can get, or rewarding. I can't go further without a way to analyze and aquire data that can be evaluated so you boys will need to run on your own. I'm fairly confident in the theroy and op's and at this point it's good to see the veiwpoints and confidence of each in their systems.

This post started as an invitation to you from ktmlew about cv's and strayed a little. I suspect it should head back that way.

PK

 

[marcusgunby]

Heres the latest CR450f forks piston(thanks thomasw) hows that for a large port??these seem to be praised as the best working std forks ever released.

I find its a rearity for mxers to want to spend the extra on aftermarket pistons.So i work with std.

 

[terry hay]

PK
You're absolutely right. We have digressed, which was not intentional but I guess we just ran with it. Back to the CV. My conclusion to replace the valve entirely was a decision based on testing with various options with the CV in place. I believe that if yamaha re-released their 96 fork internals in modern guise it would be considered a leap forward. (Recirculating cartridge - 48mm tubes)
Terry

 

[marcusgunby]

All the best threads digress:) or should that read are 'degressive'

 

[KTM-Lew]

Hey. all.....keep talking and thinking....as the kids say "it's all good'!

 

[PMK]

Marcus,
Not to head back to the non cv subject but for a moment I shall. I suspect that with a pressure cartridge, the delta P across the shims needed to be maintained, therefore more area is needed?. In short terms the ics pressure is opposing the fluid pressure created by displacement of the rod and a restriction thru an orifice type piston may have a difficult time to give consistant shim flow.

PK

 

[terry hay]

You know what the really funny thing is ? With all our theory, ideas, concepts or flatout bullsh-t. No matter what we think is right; if the customer doesn't like it, we've just wasted our time. Thats right! At the end of the day its personal preference that is the underlying factor. We can set up ten identical bikes the same way for ten riders of equal weight and ability. We may find that 5 will love it. Two may say it's too hard and two may say it's too soft. One may just simply not like it at all. It's what you're prepared to do next that determines wether you are a good tuner or not. Will you argue the point? Or will you give the guy what he wants? There is little point in telling the tenth guy that the first five loved it. At the end of the day we start with a stock machine and hopefully we end up with a well tuned bike that creates customer satisfaction. How you arrive at that point is not as important as the fact that you got there. But it sure is cool discussing this with you guys. Hopefully we will all meet at Jeremys place for his seminar, have a couple of beers and take the piss out of him and all in sundry. Enjoy your week end guys.
Regards
Terry

 

[svi]

Originally posted by Jeremy Wilkey
Guys,
So yes many times less damping appeals to some and smaller leverage means more stored energy for equal deflection etc.etc.. (BTW SVI I'm all about digressive but we can talk about that later.)
BR,
Jer

AAHH digressive, music to my ears, been using digressive set ups for a while now and really like them. Plenty of feed back and good adjuster range at low speed whilst soaking up bumps like nothing else. I have found though that it takes some riders a long time to get accustomed to it because they say if the bike is not pounding them hard they can't really tell what it's doing.
For these riders I've been working with Velocity Dependant Pistons, again you get good low speed and a digressive mid range but can really crank up the high speed to increase the feed back at the higher shaft speeds.

 

[couchrider]

Originally posted by svi


AAHH digressive, music to my ears, been using digressive set ups for a while now and really like them. Plenty of feed back and good adjuster range at low speed whilst soaking up bumps like nothing else. I have found though that it takes some riders a long time to get accustomed to it because they say if the bike is not pounding them hard they can't really tell what it's doing.
For these riders I've been working with Velocity Dependant Pistons, again you get good low speed and a digressive mid range but can really crank up the high speed to increase the feed back at the higher shaft speeds.

 

[couchrider]

SVI
I know this is off the subject, but It caught my eye. I have seen the word "Digressive " alot I did a search on this. Just about every site that deals in suspension, has the word" digressive", but none explain it, and how it differs from conventional dampaning
Can you explain "digressive set ups" and "velosity dependant pistions"

Bob

 

[svi]

Hi Bob,
Download this manual it will give you all the information you need, if your on dial up it takes a while but is well worth it.

http://www.penskeshocks.com/8900%20Motorcycle%20Manual.pdf

 

[couchrider]

SVI

Thanks for the info on this. Alot of this stuff is a little over my head.
So standard digressive valving is nothing other than a tapered stack. according to the diagram on page 20. But it seems to me that I am missing something here, Maybe not, just a feeling

Bob

 

[Jeremy Wilkey]

Bob,
Your missing something! This is a hard topic not for the faint of heart. Do some searches and come back in after you have a little more background.. Or posibly someone on here might help you get more up to speed..

BR,
Jer

 

[couchrider]

Jeremy,

First I know that I am not up to speed, probably never get to the level as yourself and others, but can't blame a guy on trying.
I have done a search on this "Digressive" issue. (every site uses this term)
From what I know of so far is that all dampaning in certain respects is progressive in nature and this is were I am getting confused
Are you guy's talking of digressive in terms of how a stack is built or is this digressive in terms of dampaning.

 

[Jeremy Wilkey]

We are talking in terms of damping force as a function of speed!

 

[svi]

Couchrider,
Digressive relates to the increase in damping force relative to the increase velocity. If the damping force rises by the same amount proportional to the increase in velocity it is said to be linear. If the rise in damping force gets less as the velocity increases it is said to be digressive. The force is still rising just at nothing like the same rate.

 

[Jeremy Wilkey]

SVI,
Have you ever pondered how you might create and regulate a "true" digressive system? I've spent some time thinking about this... To actually ride such a bike would seem bazzare I think...

BR,
Jer

 

[svi]

Are you talking about a complete digressive system in terms of damping alone or wheel rates as well. My experiences with digressive damping systems are that up to a certain point they work really well but then the feel goes. With some kind of blow off system it should be possible to control the digression which in theory would give a far better ride platform but feedback is essential to quick lap times.
In terms of wheel rates I'm all for progression, do PDS systems with a linear spring go digressive or does the natural rising rate of the inclined unit counteract this to make it linear or slightly progressive?
I'm thinking a combination of digressive damping and wheel rates would have you riding around on the bump stops.

 

[KTM-Lew]

Bump

 

[bclapham]

kind of ironic this one came back to the top again. i just rode my 01yz250 again today and after spending a few weeks on a showa clad bike, the yz is just terribly harsh. problem is, i am running out of shims to take out.

i am interested to hear what midvalve setup anyone has had sucess with- i am running something like 27.1(3); 25.1; 22.1; 20.1; 18.1; 16.1; 14.3 clamp......with 1mm lift and a really light BV and they are still nasty. i ride really rough fast tracks so if anyone has any good experience then i would be pleased to hear- also, has anyone got a link to the RT CV replacement- a soft, mushy fork would be a bg step forward right now- at least it would move.

 

[terry hay]

Bruce
Time to put my money where my mouth is. I will send you a set of Cylinder valve replacements and appropriate valving if you are prepared to install them exactly as I state and post your results. The product is of my creation and works extremely well to overcome the misgivings of the yz forks. You may have to take your cartridges to RT in Corona and have the parts installed but I will organize for this to be done at no cost. E-mail me your address.
Regards
Terry