Machined my own shock piston

[protraxrptr17]

I got tired of having to order a whole piston from Elka everytime the seal gets worn. I always take the new one and modify it before I put it in anyway. I never have one on the shelf when I need it. I've been wanting to make my own anyway. I used seals from an automatic transmission. I can get these seals for almost nothing anytime I need them. I usually mill out the bridge between the compression ports on the stock elka piston, but my o-ring grooves are peeking into the ports, so I left it in there for more support. I wanted to make square looking ports kinda like an Axis, but I was in a hurry. I'm going to make a few different kinds and see which one works best.

[protraxrptr17]

I put two seals IDK if it'll help durability or not.

[mitch-#4yfz]

looks good. really cool

[Colby@C&DRacing]

The problem with the wear band design on the elkas is that they are not allowed to expand far enough. This leaves a very weak seal on the shock body and allows for blow by. Protrax that is an interesting design are you going to hard anodize the piston?

[protraxrptr17]

No, but I was going to ask you about that. Why are they hardened? The only reason I see is because of the shims vibrating against it. I was thinking about trying it like this and perfecting my design and then sending them out for hardening when I'm happy with the performance. Do you see any short term problems? Got any suggestions on port design? Those ports look kinda hacked up because I don't have a CNC mill yet and I didn't have time to do it on the old manual (I gotta ride tomorrow:eek: ). I just did it with a die grinder while I was waiting on something else. I can turn out the blank piston in just a few minutes on my CNC lathe, so I can afford to try a few different designs.

[Colby@C&DRacing]

The piston looks good. Your right the hardening is for face wear from the shims. They will work for now raw. As for the design it may be a little restrictive for your needs on the rebound ports.

[TNT]

I dunno how shock shims fit up or wear but we anodize aluminum aircraft parts in the proximity of fluids and solvents to prevent corrison. Just curious what alloy of Al did you use protrax? 7050?

[protraxrptr17]

Colby, this is for the rear. I'm gonna really try to do something different on the front to get more rebound flow. This should be OK on the rear because it's basically the same as the Elka???? Actually the holes are a touch bigger. ANy ideas on what I should do to make it flow better? I didn't take picks f the other side, but I ported the rebound about the same as the comp.

TNT, Its just 6061. It's probably not the best for this application, but it's what I had laying around.

[number52]

I wouldn't recommend the round hole design like elka uses at all on the compression side. You will be chasing your tail trying to get it to flow properly if you use any more than a .15 shim then a crossover shim next to the piston. You should have plenty of flow on the rebound side though as it is now. You're moving in the right direction with the Axis design in my opinion. And remember that it's not the size of hole that directly effects the flow that the valve shims control either.

[TNT]

Protrax get some aircraft grade 7150, 7175, or 7050 more common no need to hard anodize it if your billet size is less that 3" your ST grain direction vertical(LT is length less compression more tensile but is weaker meaning the length of the billet stock block), will not need hard anodize for surface friction. try it. Used for major wide body al MAJOR aircraft frames and Pressurized BULKHEADS that see 1000s lbs of load in compression. Buy it cad plate if you can, or passivated for al/hyd fluid corrosion but that will only happen after 5-10 years so machine it bare and use it you'll be fine. :D

Listen machined al or ti is all about grain direction lots don't get this machine 90 degree to the extruded grain ST like you did, extruded plate less than 3inchs is the best strength. Extruded block or "plate" or "billet" , machining itself cold works provides HUGE strength with the right machinable allow, 7 series!

6061 is good for welding but lacks compression properties and friction coefficent compared to 7XXX, 7 series will cost a little more.

Good job machining impressed!! :D

[TNT]

If you want to see the compressive mechanical properties of 6061 vs 7050 let me know and I'll post them or just take my word for it.

Terry :D

[protraxrptr17]

I used 4" round for this. I have never thought about the grain direction. Which way would it be? I know 4" is alot bigger than what I needed, but I have a 8' drop from a job:D

I just came up with a way to cut rectangular holes without a super small endmill and taking a bunch of time. I think I'll drill a starter hole and then grind a HSS tool blank into a broach the shape of the finished hole. I can make a fixture to hold it and locate and then I can make the holes in a matter of minutes instead of hours. I can port them with the die grinder again. Its raining here today, so I didn't get to try it out. :mad:

After thinking about it, the o-ring groove getting into the comp holes may be beneficial. There is an o-ring under the hard plastic sealing ring. Under compression, the oil should go behind the o-ring and push it and the sealing ring out against the cylinder wall. Kind of like a compression ring in an engine. Agree?

[TNT]

Yeah that extruded bar your using has the grain in the direction it was extruded so your good for compression.
Sounds like a good idea, think what your saying is you'll build a milling guide tool to make square ports, drill as big a starter hole as possible then use a small mill cutter to clean it up square.

I'd speak to the rest but not a shock guy have not seen the o-ring and plastic part fit up. Got time take some pics or show me a diagram I'll try and give my .02.

I need to dig into shocks some day too busy with sealants and ECU's right now. :D

[protraxrptr17]

You are right about drilling th starter hole, but the custom tool will be pressed thru the piston to cut out the corners of the round (drilled) hole. To cut it with an end mill, I would have to use like a 1/16 oor something to get the corners cut out. Very tedious with the machine I have. It's pretty big and has some slack.Too cumbersome to runa tiny end mill. Plus, this would be much faster.

[motardracer]

Certainly not as much fun, but you could just buy the Axis pistons, if you like their design, and machine them for your piston band to fit.... Just a thought....

[dustin_j]

Originally posted by protraxrptr17

After thinking about it, the o-ring groove getting into the comp holes may be beneficial. There is an o-ring under the hard plastic sealing ring. Under compression, the oil should go behind the o-ring and push it and the sealing ring out against the cylinder wall. Kind of like a compression ring in an engine. Agree?

I was thinking the same thing.

Colby, what are your thoughts on this? I would also be interested to see what your CNC pistons look like if you wish to share them.

GT Thunder has pics of their pistons on their website you could check out. I also have pictures of Santo Derisi's Works replacement pistons if you're interested.

Sweet project! Too bad you're so far away, I'd love to help with R&D:cool:

[Colby@C&DRacing]

I have some pics of the pistons we use on here some where I will try to find them. I have never seen a wear band that is pressured from behind with fluid but it could work.

[protraxrptr17]

It's prolly not necessary, and I didn't intend it to end up that way, but it may help.

I would love to see some different pistons. I worked on some PEPs once that I want to see again. Seems like they had fixed orifices and check balls instead of shim stacks. Am I dreaming that?

[Colby@C&DRacing]

No you weren't dreaming the older PEP front shocks were made with WORKS shock parts. They used an orifice style damning system.

[protraxrptr17]

These were prolly '06 models. I guess it worked pretty good, but it's hard for me to understand how restricting the flow like that could make for a smooth ride. Maybe they worked better for standard travel setups with a big motion ratio.

[duke416ex]

I was curious about the axis piston as well. I hear a lot of people say they can't get enough flow froma n elka shock to replace the pistons with high flow. After removing the checkballs do they still not have enough flow? Just curious, pitons look good, wish I had the equipment to try something like that.

[protraxrptr17]

Can't use an axis piston. They have a bigger hole where they mount to the shaft. I think the OD is different as well. My stock Elka piston worked pretty good after milling out the bridge. The only check ball is in the jet in the end of the shaft on rebound adjust shocks. Doesn't really do much other than stick and cause the shock to pack up. I chunked mine loooong ago. I also took out the rebound adjust in the rear (fronts never had it.) I broke a rear shaft once. I always ran it full soft anyway, so I just made a solid shaft for extra strength. (the adjustable ones are hollow)

Whats your take on this Colby? Am I crazy for getting rid of the rebound adjuster? Everytime I get on my buddies bikes it feels like they are packing up and the tires cant follow the ground. I know there has to be a stopping point, but it feels like the faster the slow speed rebound, the better. What trade off is there by running it super limp like that and letting the shim stack do it's thing?

[Colby@C&DRacing]

Rebound adjustment is nice to have in the rear to dial in the shock for changes in unsprung weight and even track conditions. But it can be a problem since most people run there low speed rebound way to slow because when they do the push test it just sames like slow is in control. You are right most of the time faster is better. The AXIS and FOX shocks use a SAE tubing size while the elkas are metric

[dustin_j]

Here are some pictures of Derisi's high flow pistons. They were out of an older set of Works shocks he converted (my brother-in-law bought the quad used). He also shows a 5 port piston on his website.

His pistons look like they should flow well, whereas the Elkas have some flat spots that would push rather than direct the flow of oil. The rebound bypass is also between ports in the piston, rather than through the shaft.

[dustin_j]

Compression Shim Side

[dustin_j]

Here's a picture of GT Thunder's High Flow Pistons (off their website). I'm still amazed at how large these ports are. I'd be interested to hear peoples' opinions on these (and other) piston designs. I would think the more flow, the more valving control.

Does anyone have any other piston pictures to compare?

[TNT]

I'd like to see a cross-section through that large port. I looks like a venturi shape, now if it is that could explain the large port effectivness more flow through a venturi creates a low pressure area....does that make shock sense?

In machining terms it does not look like the ports on right were cut by 3 axis but rather 5. One on left looks like conventional 3 axis milling like protrax is doing.

[number52]

You are all missing a very important feature of a shocks piston and how it effects the valving characteristics. It's not all about the hole size (although this does effect some of the characteristics of the low speed circuit). I will try to round up some pictures and see if you can tell the differences! If you're planning on making your own pistons then you need to know each characteristic and why it does what it does or you will be chasing your tail!

[protraxrptr17]

Originally posted by TNT
I'd like to see a cross-section through that large port. I looks like a venturi shape, now if it is that could explain the large port effectivness more flow through a venturi creates a low pressure area....does that make shock sense?

In machining terms it does not look like the ports on right were cut by 3 axis but rather 5. One on left looks like conventional 3 axis milling like protrax is doing.

It can be done with three axis. Its done by interpolation with a ball end mill. It just goes around and around the shape of the hole taking off very little material until the desired shape is reached.

[protraxrptr17]

Originally posted by number52
You are all missing a very important feature of a shocks piston and how it effects the valving characteristics. It's not all about the hole size (although this does effect some of the characteristics of the low speed circuit). I will try to round up some pictures and see if you can tell the differences! If you're planning on making your own pistons then you need to know each characteristic and why it does what it does or you will be chasing your tail!

Let's do it.

[TNT]

Originally posted by protraxrptr17
It can be done with three axis. Its done by interpolation with a ball end mill. It just goes around and around the shape of the hole taking off very little material until the desired shape is reached.

Yeah your right called Hemstitching.

So tell me low speed compression, our PEPs don't have it. Baldwin said it's not that effective on most shocks. Our Elka's thats true. He told my boy we can change our "stack" ...which he didn't understand and is going to call him back. He wants more dive/body roll in corners...I assume Balwin meant spring stack and crossovers?

You guy's agree that LS comp is not effective in most shocks, spring control is better? THese PEPs are the best shocks he ever rode and he's tried them all. What gives?

[dustin_j]

Originally posted by protraxrptr17
Let's do it.

I'm with protrax. Let's talk pistons number52!

TNT, what is your crossover gap? Measure the distance between spacers for your lightest spring (not the zps spring) with your boy standing on the footpegs. Increasing this gap will give more dive/body roll since it delays the "crossover" in spring rate. I'm not sure if this is what Baldwin was referring to as "stack."

[protraxrptr17]

I don't use any knobs. I run mine full soft. Maybe I'm wrong, but I feel like the knobs are there for the average owner to play with and maybe see a VERY small change. THe only thing I can feel when I mess with the compression knobs is a rough ride. I think if you have a problem you need to go inside the shock or do something with the springs, knobs are for rider preference. Whatever the rider likes. Just my opinion.

[number52]

I'll try and get some piston pictures up soon. Just been busy lately, I mean ALWAYS!!

What shocks are you running that you don't see a difference in the compression adjusters?

[protraxrptr17]

It's not that I don't see a difference, it's that I don't see any GAINS. I haven't found a situation where turning in the rebound or compression did anything other than make the ride stiff. That's just my personal preference. I like all the knobs full soft on any bike/shock I have tried. If the shocks didn't feel right, knobs didn't help. What I'm trying to say, is that the knobs seem to do nothing more than slow down the reaction speed of the shock. Call it what you want, high speed, low speed, whatever, they only seem to make a difference at the VERY first part of shock movement. If the shock doesn't move fast enough one direction or the other when the tire hits an irregularity on the ground (a hole or a bump), it transfers to the chassis and the rider takes the impact. I think when you walk up to your bike and push down or pick up on it, you should feel almost no resistance other than the springs. PEPs seem to be the only ones to feel right straight out of the box. I have watched many riders push down on their bike and watch how fast it comes back up to adjust rebound. I think that's wrong. I want to pick up on mine pretty fast. If the tires lift off the ground before the shocks top out, it's too slow. Theres no way the tire can follow the ground if it's any slower than that. Most of the time, it has to be full soft for that not to happen.

[number52]

Maybe the pep feel like you want them because they have the ZPS springs! I've felt good and bad on all shocks. There's no way that the shock manufacturer will get it right the first time every time.

I kind of agree with you on rebound. Just some food for thought: Are you fully compressing the spring before you lift up as fast as you can to watch the tires drop away? Think about how you want to control that spring from full compression and how you want it to react when its just coming off full compression and how you want it to react when it's getting closer to full extension? Do you want it to act differently at these two points and how do you want it to act?

Also, the adjusters are meant to fine tune the current valving in the shock. I absolutely agree with you on the rebound adjuster, set it and leave it due to the fact that it controls more than just rebound!

[protraxrptr17]

When the spring is fully compressed the shim stack should be controlling the rebound for the most part. I get what you are saying, but my way simulates something like going down a straightaway that has choppy bumps in it. You don't really get down into your travel very far, the shock is just working in the very first stage of its travel. If the rebound is too slow, your tires are going to skip over the hole instead of dropping in, then on the other side, if the comp is too stiff, it's going to jar you coming out. Alot of people I talk to are afraid to loosen it because they think they are going to get kicked over the bars on a jump or whoops. Exactly the opposite is true, you are most likely to get kicked because the shock packs up. Too fast rebound after full compression is a sign of too weak rebound damping in the shim stack, blown piston seal or low oil.

I'm not talking about spring resistance on the PEP's being plush. I'm talking hydraulic resistance.

[number52]

I totally agree with you. I just didn't know if you were yanking up on the grab bar or preloading the shock then yanking on the grab bar and watching how the wheels drop away. It's 2 totally different situations and they should both act differently in my opinion.

Also, those PEP's you're pushing down on you are only feeling the low speed bypass(rebound) hole in the piston working when you do that. I don't know why it would feel much different than any other shock out there except Elka due to the 1 way valve in them.

[duke416ex]

Anymore talk or pics on this? I would like a little talk on shim stacks. I have seen different ways of doing them and just curious what makes a difference.

[protraxrptr17]

Originally posted by number52
Also, those PEP's you're pushing down on you are only feeling the low speed bypass(rebound) hole in the piston working when you do that. I don't know why it would feel much different than any other shock out there except Elka due to the 1 way valve in them.

That's what I'm saying, the PEP's were the softest of any I have seen, excluding my own. I have strived to make them feel like PEPs because I feel like they have the best setup. All others feel harsh to me. Haven't tried some of the other tuners out there, such as C&D, Derisi, the HMF guy etc. I have tried some PEP's done by SF and they were to my liking.

duke416, what specifics do you want to know? There are so many ways to valve a shock. I like to use a bunch of thin shims. I usually have a couple small diameter shims just above my base shim and then resume going succesively smaller. I am self taught on shimming, so my ways may be wrong. I just keep trying until I get it like I want. Axis seems to use really simple stacks in their shocks. Maybe like six shims, all the same thickness, going smaller diameter in equal increments. I have worked on a few Axis and they were all built that way. I'm fairly sure they came from Axis that way. Not saying it's good or bad, just noting.

[duke416ex]

Well, I have heard of shims like that. I also hear 3 stage valving, 5 stage valving, different things. I read a little in dirt bike forums abotu some things they do that I was curious about. Like you say some will start with the larger diameter shims(not sure on thickness) and go smaller, thin go back out to larger diameters. I have seem some stacks that may do this a few times. They may not go back out to the largest diameter though. Just curious what affect this had.

Also, I have noticed some adjusters have stacks on them, how much does playing with those shim stacks change things?

[dustin_j]

Protrax, how thin are the shims you use? It sounds like you use a pyramid structure, and do you only put multiples on the face and large shims (ie, one shim of each diameter until you reach the largest ones)? How many stages do you use? Just curious what your testing has led you to prefer. I'm just getting started with my testing, and am curious if you would like to share any of your findings.

Duke, good suggestion. I also visit some dirtbike forums, solely for technical suspension discussions. It'd be great if we had more discussions like this here. It would be interesting if people wanted to share examples of their stacks to discuss and build upon. I really wonder if the 5 stage stack you saw was worthwhile?

I recently revalved my Elkas; they had 3 stage valving, but I replaced it with a 2 stage setup. I changed springs at the same time, so I can't compare the 2 stacks. Although, the previous setup was hydro-locking, so I drilled a bypass in the piston. My current stack is plush, but too soft at high shaft speeds. When spring/warm weather arrives I'll be testing/trying different stacks and can share more then.

[number52]

[QUOTE]Originally posted by protraxrptr17
[B]That's what I'm saying, the PEP's were the softest of any I have seen, excluding my own. I have strived to make them feel like PEPs because I feel like they have the best setup. All others feel harsh to me. Haven't tried some of the other tuners out there, such as C&D, Derisi, the HMF guy etc. I have tried some PEP's done by SF and they were to my liking.



I have to disagree with the PEP's valving being the best. (Unless you are talking about one of the shimmed pistons). In my testing they are hydro locking for a split second which takes control of the shaft speed and sends a jolt through your arms. This usually isn't felt, but can be easily seen on a dyno.



The Axis usually use 6 shims on their compression stack and 5 on the rebound stack. They aren't always the same thickness, just depends on which stack you have. They are very simple to go up to the next heavier stack. If you have 2 .008" shims and 2 .010 shims, then the next heavier would be 4 .010 shims.


I'll try to post up some different piston designs and you guys can take a shot at there characteristics.


There are many different ways to valve depending on what you're trying to achieve and you're piston design, although I don't recommend anything above dual stage valving.

[duke416ex]

So you have a shock dyno? I would love to mess with one a little. Thought of making one, but not sure if it would tell me enough info. I found some plans on making one though through a dirt car forum.

[dustin_j]

Originally posted by duke416ex
So you have a shock dyno? I would love to mess with one a little. Thought of making one, but not sure if it would tell me enough info. I found some plans on making one though through a dirt car forum.

Were these plans for using a compressed air cylinder? I found them too. Seems like it would work, but it depends on what forces would be required to simulate high shaft speeds.

Thanks for the input number52, I look forward to the piston discussions.

[protraxrptr17]

Originally posted by number52
[QUOTE]Originally posted by protraxrptr17
[B]



I have to disagree with the PEP's valving being the best. (Unless you are talking about one of the shimmed pistons). In my testing they are hydro locking for a split second which takes control of the shaft speed and sends a jolt through your arms. This usually isn't felt, but can be easily seen on a dyno

What causes the hydro lock? Very interested in this. I've noticed some unexplainable jolts in mine recently and blamed it on a worn steering dampner. I know what hyro lock is, but what is causing it on the PEP's?

I agree about more than 2 stage valving being unneccesary. I don't think we see a big enough range in shaft velocity to notice any change.

I used to write down everything I did to my stacks, but the last few times I have made a change, it has been in my trailer at the track and I was in a big hurry to get back out there, so I've lost track of what I have. I know, I'm gonna do better this year.:rolleyes:

Here's a compression stack from (I think) a '05 YFZ Walsh Elka. I don't know who built these shocks. It seemed a little stiff for me.

10x20
10x23
10x23
10x24
20x26
20x26
10x20
20x28
10x23
10x20
40x17
10x20
10x23
20x28
20x32

After looking at it a little harder and the frantic scribbling with oily fingerprints, this could have been one of my experiments. That 40x17 seems like some weird shims that I took out of a 200x rear shock. My notes suck so bad, no date or anything.

[dustin_j]

Protrax, I assume your left column of measurements should have a decimal in front of them (maybe this is assumed when listing shim stacks?). You're not alone on the poor notetaking! That 40x17 is a thick crossover, would the second stage even be used? Did this act like a high speed blow-off, assuming this means that high speed damping reaches a limit though shaft speed still increases? Please correct me if I'm wrong.

Here's a stack that came out of a pair of Elkas made for a 250r with +2 arms (info from Elka via serial number); not sure if anyone else touched them internally, but the springs (too stiff) were Elka's. These shocks are now on a 400ex with +2 arms; I changed extended and compressed lengths to match. The compression was harsh at best, and they would pack and hydro-lock like crazy! Of course I had to fix my rear end before I could tell the front was so bad.
Compression:
32 x 0.15
22 x 0.1
32 x 0.25
30 x 0.2
24 x 0.1
30 x 0.3
28 x 0.25
26 x 0.3
24 x 0.25
22 x 0.3
20 x 0.25
18 x 0.25

Rebound:
22 x 0.3
24 x 0.25
26 x 0.3
28 x 0.25
28 x 0.2
22 x 0.1
20 x 0.2

[Colby@C&DRacing]

No low speed damping and heavy springs always makes for a good ride;) . As for the lock on the PEP shock it comes from the holes in the piston limiting out on the amount of fluid they will flow. This style of piston relies on orifice style damping and uses the size of each hole to creates dampening which can work until you reach the limits of those holes.

[number52]

Here's the first piston with different compression and rebound characteristics. Let me know how you think each side will react?

[number52]

And here's piston #2 which are the same on both sides.

[protraxrptr17]

Piston #2 is interesting because it applies pressure all around the shim stack. Rebound has the potential to flow really well. The size of the holes looks kinda small. Maybe what I need for my mega-travel front end.

#1 looks kinda like GT thunder's design. Nothing really spectacular.

I would like to try #1. You got one with a 12mm bore and 45.35 diameter?:D

[BuckIRacer]

As someone who has made a living working with shocks, I always enjoy reading these forums, but I rarely comment. It's cool to see people playing around with this stuff and making up their own parts, I wish I had the time and resources to make my own stuff! As for those images, they are pulled out of the Penske/Custom Axis manuals. I'd be curious to know of people's opinions/theories on the digressive/linear/progressive damping from the pistons. Also, keep in mind, valve stack thickness comes down to thickness^3, which is why a single .15 shim is stiffer then three .05 shims.

[number52]

That is correct. I'm just trying to point out that there is much more to piston design than just the hole diameter. And the relationship of the sealing surface that needs to be payed closer attention to than hole size. It's very important to know what you are changing on these pistons because you could be going the wrong way really fast and not know why, especially without a dyno.

[number52]

Well since no one is else seems to want to take a shot at the sealing surface effects on these then here are the characteristics of these pistons.


Piston #1 The compression side is a Digressive Piston, which means that as soon as the sealing shims start to deflect it will blow off and flat line at that piston speed. And the Rebound side is a linear piston (most common) which means the faster you move the piston the slower it goes at a constant rate. But can be manipulated easier with shims.

Piston #2 Both Compression and Rebound are digressive with an increasing rate after it blows off due to orifice size. Some pistons will run 2 separate stacks.

When machining your pistons they also need to be perfectly flat because you can preload your shims causing them to be stiffer or blow off easier.


I could go on and on with piston holes, but I just wanted everyone to see the relationship that the sealing surface had on valving.

[protraxrptr17]

What makes them linear or digressive? Why would you need a digressive piston? Seems to me linear is the way to go. Is a linear design described by only deflecting a small part of the shim, and then gradually going more and more until the shaft slows?

Just guessing, but seems to me I have a kind of in-between digressive piston. What should I use on the rear? That's where I'm not happy. I have about 14 inches of travel with only about 3 inches of shock stroke. At ride height, it's only about an inch off the bump stop. It's really hard to make it ride smooth without bottoming too much. You can make it one or the other, no happy medium. I know I should scrap the rear setup and start over, but I don't have time right now. I'm supposed to be getting a Houser hybrid this weekend, so maybe I can shut this one down and redesign it to work better. I would still like to get this figured out though. I hate to let something beat me. I have a long travel linkage on it. I thought about going back to the stock linkage to try to get my ratio back closer to ideal, but that is still admitting defeat.

BuckIRacer, please stick around and post with us. Anybody is welcome to jump in here with us. All comments are welcome. We need to get better with shocks, it has been seen as a black art that only a few are blessed with from birth for too long. I know that most people don't need to mess with it on their own, but we need some new ideas. If more of us can get together on it, maybe we'll invent something new.

[duke416ex]

protrax, have you measured out the rear with the linkage you have adn which linkage are you running? I had trouble with an elka rear setup until I measured it out and had the shock dimensions set up how I wanted it.

What about the progressive pistons? I have noticed when looking for parts that I saw some for ohlins for sale. Could something like that not be used to act similar to an ohlins pds? I may be thinking wrong.

[dustin_j]

Alright, I'll take a stab at explaining linear vs digressive pistons. This is based on observation of number52's pistons and a search yielding many options from Ohlins and Penske.

Digressive pistons always have thin exit ports (is this what you'd call it?) on the outside of the piston. Therefore, when the shim lifts and deflects, the entire port is uncovered very quickly; once the port is uncovered, increasing shaft speeds does not create a significant increase in damping.

Linear pistons have larger exit ports that require more shim deflection to completely uncover. Therefore, as shaft speeds increase, shim deflection continues to increase, and damping increases with shaft speeds.

number52, could you elaborate or correct my thinking above. How do linear and progressive pistons compare? Are linear piston exit ports symmetric and progressive ports get smaller closer to the shaft (Think the oval shape you posted vs the pie shape of stock and GTThunder)?

Also, It would be great if you would be willing to share examples of where each type of piston would be beneficial. Also, we should compare two pistons of a given type (probably linear) to see what performance gains different variations provide. Either way, thank you for your contributions!

[dustin_j]

Protrax, I think your rear suspension would benefit from placing the shock more vertical. Do you have, or would it be possible to, get measurements from the left side (2-dimensional) with relation to the swingarm pivot bolt: The location of the top shock mount, the front linkage mount, and the swingarm linkage mount. Also, center to center measurements of the linkages, shock extended and compressed length, and total wheel travel.

I've been wanting to do this to my quad to see how the progression changes with respect to wheel travel. I could try to get a graph for you so we can see exactly what it's doing and maybe figure something out to help. You're right, going back to stock is not an option! haha.

[protraxrptr17]

Thanks dustin, that explanation opened my eyes to an oversight I have made.

As far as moving the angle of the shock, I dont think it will help much because of the design of the linkage. I have studied it many times. Moving it would cut travel. I want to totally scrap the whole linkage and run a super long shock. I forget my exact measurements, but I have come up with a no-link with a 26 in shock with some crazy motion ratio numbers. If I get this Houser bike and can stand to ride it for a few months, I will definitely build it.

The linkage just increased whell travel without increasing shock stroke which is really not good on a bad setup anyway. I have no idea on the progression, but it's supposed to be less than the stocker which is good. The whole rear end sucks in my opinion, but I'm trying to figure it out without scrapping it. If I do get it figured out, when i do get the new on done, it'll be easy to nail the setup.:macho

[duke416ex]

So what frame, rear end, shock set up are you using?

[dustin_j]

Zeb, I was surprised you hadn't made your own linkage. Now it makes sense, you have a much bigger plan in mind. I'd love to see the massive no-link setup; I bet it'd work great. Care to share any of the measurements or motion ratios? Will this be a completely custom shock? :macho

[protraxrptr17]

Yeah, I plan to build the entire shock from scratch. I would love to make it an external bypass, but I gotta think babysteps. I haven't drawn any plans yet, just messed around with a tape measure and some wire. It's been a while so all the measurements I had in my head have faded. I want the motion ratio as low as I can get it. Seems after you cross under 2:1 it gets really niiiice. I have proven that with my front end. :D The rear of the frame will have to extend out to about the end of where my air filter is now. One of those new Yamaha engines would make all that easier but I don't see myself gettin one of those for a while. The shock will mount at the front of the carrier. Maybe that will give you an idea of what I'm going for. I'm sure some of you see the benefit, but what I'm going for is much more variation in shaft speed that the lower ratio gives. I know linkage is supposed to be for progression, but I think it has more to do with clearance issues and ease of manufacturing. What I'm saying is, you can get better ratios with out stretching the shock mount to the back of the swingarm with linkage. The trade off is added stress to the swingarm and frame and it makes it harder understand what the springs and valving is doing (for me anyway)I wanna throw out the linkage and do it with valving and springs.




I have wanted to make my own linkage, but I can't figure out a way to make it any better than it is.

[protraxrptr17]

Originally posted by duke416ex
So what frame, rear end, shock set up are you using?

It's kind of an '01 Raptor frame, but mostly its my own stuff. Lemme see if I can find a couple pics. The shocks and linkage are Elka. The swingarm is a JRD that I had him custom make from my own measurements. Supposed to be '86 250R length with Raptor geometry. The Raptor platform isn't too bad when you get the weight off, which I did when I got rid of the giant engine.

[protraxrptr17]

Here's one

[protraxrptr17]

Front

[protraxrptr17]

Anybody feel free to comment.

[protraxrptr17]

Hope it ain't too big

[protraxrptr17]

Ha! I just noticed that's the old 525 engine. Disregard that. It's got the RF4 engine now.:macho

[dustin_j]

Zeb, your quad continues to impress me. I think you're going down the right path; I'd love to see the swingarm you end up with. By dual bypass are you thinking something similar to the Ohlins TTX, or more like an offroad truck?

What is your frame height at full extension and full compression?

What's are you using for shock reservoirs, they don't look like Elka cylinders.

[protraxrptr17]

EXTERNAL bypass, like a King for an offroad truck. You don't need no damn linkage if you have that.:D

Full extension is about 15 1/2, full compression is about an inch.

I just bead blasted the stock reservoirs. They aren't really Elkas anymore so I wanted to make 'em look different.

[dustin_j]

Oops, external bypass. They look pretty sweet. Go pick up the hybrid so you can start on it!

[BuckIRacer]

Going back to the piston designs. Yes, everyone is on the right track with the linear vs. digressive pistons. The shims seal around the outside diameter with the digressive, therefore minimal oil flow results in opening the stack and and large "dump" region, where as the linear concentrates all the flow at 3,4,5 specific smaller areas on the shims, resulting in less of an immediate fluid dump, and a linear opening. The damping "force" is generated by a pressure differential across the piston (and some at the adjusters on the reservoir). If this pressure is allowed to be spread over a larger shim area, less deflection force is required to bend the shim. Think of a cantilever beam, fixed at one end, force at the other, now revolve this 360 degrees and you get a very basic shim (this is actually used in some crude math models for shim stack simulations).

I don't know of a big push for digressive setups in off-road applications. (Not saying it's not used, just not as common as linear). The digressive comes from a road car or race car needing good low speed control for chassis stability, and then blowing off at higher wheel impacts as to not upset the chassis. Linear works well for offroad to get a consistent damping feel.

And 52 was right, some pistons use the dual stack on separate sealing surfaces) approach, such as the Piston #2 (the Penske VDP). This causes a whole other level of complexity and headaches, and while it's versatile, it's usually optimal to stick with a traditional piston and valve stack.

The linkage is helpful because it allows to speed up the damper motion as the wheel travel begins to bottom, resulting in an increase in damping or bottoming resistance. This is achievable with a no-link setup with a progressive valve stack (though not as easy to control).


Again, it's cool to see people discussing and playing around with this stuff!

Just to give a little background on myself, I worked at a major suspension company as an R&D/Test engineer, starting in automotive mass production, then moving into motorsports support working with A-level and Works level suspension. I then worked as a Damper/Data engineer for an IRL team, so I'm spent a lot of time trying to put an engineering validation on all the "black magic"!

[number52]

Just wondering why you made new shock towers in a more upright position? If it was to reduce the leverage change due to angle of the shock I really don't think it's enough that you would ever know. Why would you bottom out so close to the ground when you have so much wheel travel already? I'm sure the tall extended length height is only for desert racing and would only be good for straight line. Curious how much bump steer you have throughout that long range of travel?

Not trying to get off subject, but the issues you mentioned should have already been addressed before ever changing your valving in my opinion.


I think you should have picked a better frame geometry to start off with for your project if you want it to work any better. Especially for a no link. Probably what you had at the time?

I've ridden many no links and they work good, but take TONS of R&D to get just right. They are easy to bottom and smooth initial or resistant to bottoming and harsher initial. There's a fine line. All of you're progression is built into the spring rate. One advantage is that they transfer and react quicker.

I still prefer the linkage because it can be manipulated much easier and initial and ending leverage can be changed to your liking. It only takes about 30 minutes to design a new link for a Honda with the progression rate I want. Like I said before, this should have been addressed before valving.

Here's a question for everyone to ponder: What is valving controlling? It's easier to think of what the rebound is controlling.

[number52]

I would use the digressive in a TT application with a close backing washer to start a rising rate after the shims deflect so far.


I don't think there is a "black art" to it, just a lot of common sense and really getting down with a microscope type of thinking to see exactly how everything works. I'm the type that tears things apart just to see how they work I guess. And a lot of thinking of how to make a quad work better. I'm always open to any new suggestions and don't claim to know everything. After doing this for a while everything just seems to fall into place! Sorry for rambling

[BuckIRacer]

I agree with number52 on the linkage setups. I prefer the linkage design over a No-Link. You should design a linkage/motion ratio and then valve your shock around that, not vice-versa.

As for what damping controls, I'll the that to others, I already know the answer! haha!

[BuckIRacer]

Yeah, TT would be a place to try the digressive.... need for chassis control, not much need for bottoming or fast damper velocity control.

Something interesting as well is that you can build countless different shim stacks, that appear identical on a dyno, yet perform entirely different on the car/bike/quad. That's when it starts going beyond the basics!

And the benefits to controlling damping through orifice flow, shim deflection, adjusters, etc, and how each plays into the overall operation.

Good stuff!

[protraxrptr17]

I moved the shocks simply because I wanted more stroke length. The originals had 3 1/4 inch stroke. They now have 7 1/2 with 15 inches of travel. The average is 2:1. I'm sure it may be more or less at different spots in the sweep, but it works. The front really doesn't bottom as close to the ground as the rear. I made it adjustable too. I only race motocross so optimum is 1 1/2". The rear gets closer because, like I said, I have always planned on changing it anyway.

As far as picking a better frame, I don't really understand what your saying. I can make it whatever I want. I bought this bike brand new in sept '00. It's probably the first significant thing I've ever had that was brand new. I got the t-pins, axle, shocks and a few things to make it raceable. Did that for a couple years and decided the 660 sucks for motocross. The YFZ had just come out and many told me to cut my losses and get one. I like to do my own thing, so in 2005 I sold the 660 engine for just enough for the 525. I parted out my Cannondale for enough to buy some extras such as axle, swingarm, materials etc. I had no money, a 8x10 portable building, a nice TIG welder, a grinder, a drill and some tools. I did the engine swap and was happy with the way it turned out for the most part. I enjoyed doing it and it inspired me to quit logging and buy the shop I have now. If I had went the way of what most people told me I would probably still be logging and have a wore out 2004 YFZ. Now, it's important to know, when I say I'm not happy with this rear end, it's still better than probably 99% of what everyone else is riding. I'm just always trying to make the next step. OK, enough of my life story.

Ya'll want to help me design a linkage for it? I'm all ears. I know the CR500 used to be the gold standard, but I've rode those and wasn't impressed. They were good, but not really that much better than what I have.

But still, if I could build an external bypass shock, why would I need a linkage? I would have to run a dummy to hold the springs so I could use one for that I guess. I can see maybe where that would be a little beneficial. Still don't see a huge benefit of a linkage IF, and only if, you have a super long stroke shock. Yeah, I understand for your ordinary average no link that everybody has done. (this hybrid I'm getting has one) I have no schooling or dynos or worked on any race teams, just daydreams, seat of the pants, and try this and see if it works.

What is ideal for a linkage? there has to be a number or explanation. I have always heard "Ahhh, you gotta have a linkage, sucks without a linkage, KTM motorcycles suck because they don't have a linkage." Not being a smartass, but elaborate please. I don't have a linkage on the front and it feels like heaven.:confused:

[number52]

If you mounted your upper shock to the frames original location and maintained the same leverage ratio with 15" of wheel travel you would still have 7.5" of shaft travel. Just shorter bodies. I like people who think outside the box like you do.

Your rear end is going to have to be completely re-engineered like you said to get it to work.

[dustin_j]

number52, wouldn't Zeb's more vertical front shocks better match/parallel the arc that the wheel travels? The closer shock path is to wheel path, the less work your shock has to do since it isn't fighting angle change in the a-arm. I guess a better way to say it would be it isn't fighting scrub, but controlling the wheel. I know the two are connected, but shock orientation would determine how much each affects shaft speeds.

Zeb, if you are willing or able to get the measurements I posted before, we could throw some linkage ideas around for you. A redesigned linkage (and possibly shock) would be a quicker project for you, though it would still be cool to be the first with an external bypass!

I also noticed number52 thought your setup looked like a desert setup. How does having that much travel compare on an mx track. GT Thunder's website raises good points that having too much travel could result in too much weight transfer on holeshots and down hills. But then again, more travel results in more shaft movement to control. Again, props to Zeb for going against the grain!

[protraxrptr17]

Originally posted by number52
If you mounted your upper shock to the frames original location and maintained the same leverage ratio with 15" of wheel travel you would still have 7.5" of shaft travel. Just shorter bodies. I like people who think outside the box like you do.

Your rear end is going to have to be completely re-engineered like you said to get it to work.

You are overlooking a few very important things. First, the bodies cannot be any shorter than they are now. The piston travels te full length. I made the shaft as long as the body would allow. Then I figured out how it needed to be mounted.

2: If I mounted these shocks in the original location on the frame, the ride height would be about like a Gorilla lifted grizzly. The tie rods would lay on the frame and the steering wouldn't work.

3: The further outboard you mount the shocks the lower the ratio until you go past vertical. I built the a-arms after I built the shocks. I put the shock mount as close to the wheel as I could get it. Then I built the mounts with 2X4's layed down flat under the frame with the shocks fully retracted. I spent MANY hours studying and measuring to determine the upper mounts. It's not as easy as it looks. Many things come up that you don't see at first. Dustin nailed it in the first part of his last post.

dustin, you can have too much travel. I'm probably at the threshold. Tire scrub becomes a problem if you get way out there. Bump steer can become a problem. I have not measured this one, but just eyeballing it there is none. This frontend is the best in the business. Mark Laeger knew his stuff. It looks like a desert bike in the pic because it is at full droop. My ride height is about 6 1/2 right now. I'll say it again, the front is heaven. The rear is not bad as it is, it's more like south florida. :cool:

[dustin_j]

Zeb, I'd love to see a video clip of your quad on a track if you get time before tearing into it again. South Florida would be great right now...

[dustin_j]

Zeb, have you been trying the pistons you made? How do they work, and how are the seals you used?

[protraxrptr17]

No, it has been raining and cold every weekend. It's looking better for this weekend. I have an arenacross saturday and I'll probably get to ride somewhere sunday. It's supposed to be kinda cold, but I'm going anyway.

[Rootar]

i know you liked your rear shock this weekend zeb, you didnt think you were going to but you ended up liking it!

[protraxrptr17]

Yeah, it felt better than ever. It was an arenacross though. The real test is outdoors. Supposed to rain AGAIN this weekend. :mad:

[Rootar]

i got a 04 and a 07 linkage (For under a $100) coming to try out on my bike, you call axis yet? its past 8am their time now.

[protraxrptr17]

Yeah, just gettin the clevis. He told me how they do it without f-in up the chrome. I sent him some pics and I'm waitin on him to get back to me. Ima have you call him with your credit card # in a little bit.

[dustin_j]

What all did you change on the rear shock? Just the Elka replica piston? Glad to hear it worked well.

[protraxrptr17]

Yes, I didn't mess with anything else. I was suspecting the band was leaking on the old piston. I was pretty happy with the valving, so that was all I changed. It would unexpectedly blow through on hard hits.