Suspension: Koni strut servicing

Discussion in 'Workshop Forum' started by Dr.Jeff, Jan 20, 2019.

  1. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I have a set of 4 Koni struts for the X1/9. They are new (as in never been used), but old (as in manufactured back in the 80's). Due to their extended shelf existence I decided the best thing would be to service them before installation. In this case I refer to a "service" as a complete tear down, inspection, cleaning, seal replacement, fluid replacement, and reassembly. This is opposed to a "rebuilding", which would include those items plus replacement of the bushing, any worn/damaged parts, and possibly revalving. I did not take photos until most of the work had been done but here is a brief summary (not intended to be a detailed "how to"). The photos I have (at the end) will help to follow the description, but a little back and forth may be needed to see things as we go along.

    These Koni's were specifically made for the X1/9 application, to replace the stock struts. So they had standard spring perches and install using the stock mounts. Their dampening is 'adjustable', but only for rebound (compression is not adjustable). I'm not sure how their valving compares to the original stock Fiat struts, but imagine they were considered an upgrade and therefore firmer. Depending on the springs utilized, the dampening could be externally adjusted to suit. For my use I am converting them to coil-over units. Therefore I cut off the stock spring perches and added retaining rings to allow the addition of threaded collars. The springs that will be used are stiffer than the stock springs but not by a lot. I want a decent quality ride for normal street driving, but a little firmer for handling and to prevent bottoming out - they will have an adjustable ride height enable lowering the car (purely for aesthetics).

    Disassembly begins by removing the top nut (collar or cap). These nuts have a pair of holes in the top of them and round circumference. Therefore you can't use a regular style wrench, but must use a special removal tool. These tools are available but not worth the cost for my needs, so I made one. I also made a simple wood fixture to hold the housing in a large vice while working on it.
    After that nut is removed, the seal / rod-bushing assembly is pulled out. This does not come out easily; there is a O-ring to seal it into the outer tube (housing), and some sort of force is needed to slide it upward. I fashioned another tool to do that, utilizing a slide hammer and adapter piece. For reassembly, the seal/rod-bushing assembly must be pressed back into the housing. I used a couple of left over urethane bushings to do that.
    Next the main shaft (rod) can be drawn out, along with the inner tube assembly. The bottom end of the inner tube holds a valve disc assembly. Connected to the end of the main rod there is another valve assembly. One valve controls compression movement, the other rebound movement. There is a stack of thin discs in these valves. By replacing the discs you can revalve (tune) the dampening action as desired for compression and for rebound. For my needs I wanted a slightly firmer overall dampening effect but did not want to completely revalve it. So I replaced the fluid with a heavier weight suspension fluid instead.

    Although these units had never been used the insides were rather dirty. The original fluid in them was petroleum based and degrades over time, even without use. Plus a minute amount of moisture in the air trapped inside them contributes to further decay. To thoroughly clean them, everything needs to be completely disassembled (including the valve assemblies, etc). Keep track of all the little bits and be sure to replace them the same way they came out. I used synthetic suspension fluid of approximately 40% heavier viscosity. But that does not equate to a 40% stiffer action (it has less of an effect than the numbers might suggest). New Viton seals and reassembly in the opposite order.

    Here are some pics. They were taken during assembly, but I will show them in reverse order to represent disassembly:

    1) The complete strut assembly, with modified outer housing and coil-over threaded sleeve.

    2) The outer tube/housing and the inner tube dampener assembly.

    3) Top nut/cap. Notice pair of small holes through it (not well shown here). The removal tool has a pair of pins that attach into these holes.

    4) Main rod/shaft and inner dampener tube. The rod slides through the seal/bushing assembly. There are two disc valves; one is on the inner tube, and the other on the rod.

    5) Close up of the two valve assemblies. These are what can "tune" the shock ('revalving') by changing the discs inside them.

    6) Close up of the main rod seal and bushing assembly. There are two seals; a O-ring to seal the assembly to the outer housing, and a lip seal to seal the main rod as it travels up and down. The lip seal is what wears and allows fluid to leak outside of the strut. A sleeve bushing inside this assembly is what the rod rides on. When it wears the rod gets side-to-side play, allowing other things to wear out quickly.

    7) Some simple tools I made to work on the Koni's.

    Later I might take a photo of the completed coil-over strut assembly ready to be installed. I can also give a few more servicing details and photos if requested.
    mkmini, avusblue98, 128kid and 5 others like this.
  2. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Someone asked me about the valves that can be tuned. Here is a little more detail, but again no pics of everything completely apart (sorry).

    004 - Copy.JPG

    Both sides of the valve on the end of the dampener (inner) tube:
    006.JPG 007.JPG

    The two valves are very similar. Each has either a screw or bolt in the center that holds all the parts together. Removing that fastener allows the discs and other pieces inside to come apart. Basically as the fluid is forced past the discs/orifices, the small passages restrict the rate of that flow. The number and specific design of those discs (and other parts) changes the flow rate and therefore the dampening characteristics. One has a coil spring, the other a wave spring inside. The springs make them a 'one-way' valve; fluid can pass fairly freely in the opposite direction. That is how one valve controls compression and the other rebound. Even changing those springs, as well as the retaining end plates, can alter its function. By having two separate valves, one for compression and one for rebound, the two functions can be tuned independently.

    As you can see, one valve is attached to the end of the main rod (the piston), and the other to the end of the inner tube. The outer strut housing acts as a reservoir for the fluid. And the inner dampener tube is where the piston (end of the main rod) travels inside. The inner tube and piston are a calibrated fit (wall clearance), so the fluid must pass through the valves as the piston travels.

    Looking at the first and third pictures above. The two tangs on the piston valve (first pic), either side of the retaining bolt, can engage with the two recesses on the back side of the dampener tube valve (third pic). When the main rod is completely compressed, those tangs and recesses interlock. Turning (rotating) the main rod from the top (externally) turns that rear portion of the dampener-tube valve. That changes the flow rate past the valve. This is how the unit can be "adjusted" externally for rebound. There is approximately 1 3/4 turn of movement possible, proportionally changing the flow. One potential problem with the unit's design is the valve on the end of the dampener tube is a press fit onto that tube. For some reason it is not a tight press fit; most of mine just fell off the tube when disassembling things. Therefore when the rod is compressed and rotated the entire valve can spin inside the tube, preventing any accurate adjustment being possible (the whole valve rotates instead of just half of it). During reassembly I peened the end of the dampener tube to help better secure the valve in place.

    For a thorough cleaning it is best to disassemble the valves and clean the individual parts. Being small orifices, that is where debris will tend to collect, much like cleaning the inside aspects of a carb. Especially being located at the bottom of the entire strut assembly where stuff gathers. And those orifices are what control fluid movement (dampening).

    These valves are the heart of the shock/strut, they define its characteristics. Koni offers a selection of replacement parts to help tune it, but knowing what specific ones are needed would require a shock dyno. And as mentioned, every part of the valve plays a role in its performance. So to properly do a revalving you probably need to send the unit out to be done. Likewise if the bushing is worn it is difficult to replace without the right equipment. But the shock unit would need to be very used for that much wear of the bushing to happen. The main rod itself can also wear. In some cases it can be rechromed to bring it back to specs. But to get it to the right finish and size might be difficult, otherwise it will allow the lip seal to leak. For these reasons doing a 'service' rather than 'rebuild' yourself is more practical. Just cleaning, replacing the seals, and changing the fluid makes a big difference.
  3. 128kid

    128kid Courtney Waters

    Essex Junction, VT
    Thanks for posting this. Great info! Where did you source replacement seals - direct from Koni, aftermarket or hydraulic shop?

    Having recently done a full service on a modern mountain bike fork, the Fiat Konis look pretty simple!
  4. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I've also done mountain bike forks before and they are kind of similar. Really all dampeners are.

    Getting the right seals for Konis sort of depends....
    The O-rings are nothing special. I opted for Viton only because I feel like they are a bit more durable, but it isn't necessary. Suspension fluid is hydraulic fluid with a couple additives, so it is compatible with pretty much all seal materials.
    The top main seals are basically "lip seals" (often referred to as 'shaft seals'). However the exact design differs on various Koni units. Even the sizes can be odd (non standard). Mine happened to be a match for some rather generic (although not extremely common size) hydraulic lip seals. But not all Konis are. You won't know for sure until the seal is removed and identified. And the way that Koni mounts them, you will destroy what's left of the seal getting it out. So a bit of a crap shoot. However Koni does offer most of their old seals, but at a price. I have a hydraulic seal supply house that gets me just about anything I need and they found some that worked at a very good price (a fraction of what Koni wants).

    I didn't mention it but Konis can have a lot of deviations from model to model. For one thing there are units that have external adjustment for both compression and rebound, which are very different inside. And there are other levels of performance such as Koni 'red', 'orange', 'yellow', etc. A long time ago I went through some Koni shocks (not struts) for another vehicle and they only had one valve assembly inside (instead of two) that served both compression and rebound functions. In the case of the ones that I have for the X1/9, the front and rear units are different. The ones I showed earlier have a slightly different arrangement for the top nut, seal/bushing assembly, and lower piston than the other pair (front vs rear). They function the same and the general servicing process is the same, but the details differ. Plus their designs evolved slightly over the production period. Which is why the exact seals may be different from one to the next. And that's why I decided not to do a step by step 'how to' tutorial.

    But I can offer a couple other general guides. The fluid inside comes in a selection of viscosities, roughly from as little as "1 weight" to as much as "40 weight" (and I'm sure there are more). According to the Koni engineer I know, they use their own proprietary blend of fluid (pretty much every dampener maker does). But it really isn't that critical to use their blend. However the viscosity you choose will make a difference on how the unit performs. He said these can use as light as 10 wt to as heavy as 30 wt. The original fluid for mine (remember it can vary from one to the next) was 20 wt, but I went with 30 wt for the stiffer springs I'm using. Another factor is the quantity (volume) of fluid. This actually makes a bigger difference than the viscosity. There needs to be some air space inside these sealed units, the balance of air and fluid changes the dynamics. He told me my fronts should have 240 mL and the rears 230 mL of fluid each, which is interesting because the rears are longer and can hold more fluid. I chose a synthetic fluid but it is available in different blends. The most affordable fluid source is motorcycle supply stores. They carry a wide selection at a great price. Or again you can get the actual Koni stuff for a lot more money.
    128kid likes this.
  5. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    NOTICE to CARL: this content refers to the damaged Koni strut from your recently wrecked car. You may not want to view this post if it is too soon and the wounds are still healing. Sorry.

    As most of you already know, Carl recently experienced a very unfortunate event where an idiot driver totalled two of his X1/9s. On one car the damage seemed to focus on the rear wheel/suspension area.


    This caused significant damage to the Koni strut that was on the car. I asked Carl if I could play with the old strut to assess the damage to it. He sent it to me and today I tore it apart. This also gives an opportunity to add a couple photos that I omitted in my earlier posts (above) on rebuilding Koni struts.

    Here is what the strut looked like after the accident:
    009.JPG 010.JPG

    The first step in disassembling (or rebuilding) a Koni strut is to remove the top nut. These are typically very stubborn, so a lot of clamping force and leverage is required. To secure the strut in a large vice, I use a simple wood jig made from a piece of 2X4:
    012.JPG 014.JPG

    The top nut has two holes in it. A "special Koni tool" is required to remove the nut by inserting it into the two holes. I don't have that tool so I made one from a old 'Crescent wrench' and a couple pieces of round stock:
    011.JPG 016.JPG

    Tool in position:

    Top nut removed. In this case the nut and the seal/bushing assembly came out together. They are actually rusted together. Normally these should be two pieces, as seen in my earlier photos (see posts above):

    Here is the top portion seen up close:

    I've reached the 10 pic limit, so continued in next post....
    128kid likes this.
  6. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Looking at the upper seal and bushing assembly, we can see the bushing (where the main shaft rides):

    And the seal on the other end (upper most portion of the strut tube), where the main shaft is sealed:

    Old suspension fluid looks very nasty:

    You can see that the inner metal sleeve that the main shaft and piston travel in was damaged. It isn't obvious here, but the tube was bent (long axis) as well as dented (seen here):

    This illustrates how the shaft and tube are bent relative to one another. Notice the difference in the gap on either side:

    As it so happens, this strut was on its last leg anyway. The main shaft has scoring (see pic), allowing the top seal to leak, therefore the fluid was contaminated with water due to the leaking seal, which resulted in rust on some inner components. So it would not have lasted long. The seals and fluid could have been replaced to extend its life a little, but the other issues would eventually kill it:

    Just because I like to cut sh*t up, here are some views of the damaged outer housing:
    032.JPG 034.JPG 036.JPG
    Last edited: Feb 14, 2019
    Stoney#1, 128kid, mkmini and 2 others like this.

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