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  1. #1
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    Marzocchi MX Comp: Coil to Air conversion?

    Tried the search and didn't really come up with anything...

    I have an '04 Marzocchi MX Comp 29er fork. It is a coil/oil fork, 75mm travel. The springs it came with aren't quite stiff enough for me, I'm ~250lbs. My 26" fork (which is no longer in use) is an '07 MX Comp air fork, 80mm travel.

    I haven't been able to find any stiffer coil springs for the older Marzocchi, so I was thinking it'd be possible to either swap the internals of the air fork to the coil 29er fork, or just put the lowers of the 29er fork on the 26" crown/stanchions/internals. They're the same width, so I think it'd work. However, do you think the 5mm difference in travel is going to make it not work? Or, more simply, anyone know where to find some stiff coil springs that'll work in the old 29" fork?

    Thanks.

  2. #2
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    Mx Comps are so simple that both (air & coil) versions have the same parts (seals, internals, etc).

    The question is, how do you adjust the preload on your '04 Mx Coil??

    If the preload is adjusted by a knob that you can turn it will be difficult, since you'll have to buy some compatible top caps with air valves on them (just like your '07's Mx) and remove the springs.
    Last edited by Pableras; 07-16-2008 at 02:09 AM.
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  3. #3
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    According to the '04 manual, '04 Marzocchi MX Comp 29er has air preload, just like my 04 Z1 FR and '05 MX Comp.

    There should be a Schrader valve under one or both of the dust caps at the top of the fork. You just need a shock pump to adjust the pressure.

    The user's manuals are available for download at Marzocchi's website.

  4. #4
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    Nope, no schraeder valves on the '04 MX comp 29er, at least not the one I've got. Both legs have a twisty knob for preloading the springs. Both are maxed out and not stiff enough for me.
    I'll give it a go and see what happens. The only thing I don't know how to do is set the oil level. I'm a mechanic, but my experience with suspension is pretty slim. I quit messing with my fork when it got more complicated than taking off the lowers and adding some Judy-Butter...
    Thanks for the help.

  5. #5
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    What I would do....

    and it is very simple, is go one side coil, one side air. This was pretty much a standard configuration on various models of the 26" MX Comp and MX Pro forks from about 02 or 03 on. I would choose the non-damper side for the air side as oil level is not as critical on the non-damper side. From there all you need to do is locate an air top cap for a 30mm stanchion Zocch fork. Remove the old top cap and preload adjuster, then remove the coil spring in that side and install the air top cap. Use the air side to set your sag and go from there.

    To set the oil level for the air side it's pretty easy. Pull both top caps and compress the fork completely. Shine a light down into the stanchion tube and observe the level of the oil on the side you intend to set up for air. You should be able to see the top of the pumping rod under the surface of the oil. As long as the end of that pumping rod in under the oil surface at full compression you are good to go. I usually try to maintain the level so that the pumping rod is at least 5 to 10mm below the oil surface. Once you have the level set, you'll need to cycle the fork a few times from full compression to full extension and observe the side you are adjusting. Watch for air bubbles that indicate the pumping rod is sucking in air etc. As you cycle the fork the oil moves so you may have to add a bit more to prevent air incursion. Using the minimum amount of oil in the air side will give you the largest possible volume for the air chamber you are creating. This will minimize air induced stichion as much as possible.

    From there button it back up, set your air pressure to achieve proper sag and go ride. Take along a LOW PRESSURE air pump and adjust the air pressure up or down as needed to suit your tastes and riding style. It's not a perfect set up, but it will work.

    The conversion is actually quite simple and realatively inexpensive. The tough part can be finding the air top cap for your fork. What you will need is a single schrader valve air assist top cap for a 30mm stanchioned fork. They should be available online.

    Good Dirt
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  6. #6
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    Well it worked, sorta. I took the top caps off both sides, and after looking at it, I realized I could just remove the springs and spacers and put the schraeder valve top caps from the newer fork on it. Couldn't be any easier... I thought. Pressurized both legs to about 60 psi and took it for a spin around the driveway. It seemed to be working perfectly so I took it back inside, only to notice oil gushing from the right fork leg! The arch is a separate piece on these older forks, and they had separated from the lowers. There is now about a 3mm gap there. It looks like the brake boss that threads through both pieces was holding them together. I had removed these, since I'm using disc brakes. I'm going to take the fork apart, see if I can hammer the legs/arch back together, put the bosses back in, and see what happens. It seems to me that the issue with the arch separating has nothing to do with the recent air conversion, but perhaps I'm wrong. We'll see how it goes...

  7. #7
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    Quote Originally Posted by willapajames
    Well it worked, sorta. I took the top caps off both sides, and after looking at it, I realized I could just remove the springs and spacers and put the schraeder valve top caps from the newer fork on it. Couldn't be any easier... I thought. Pressurized both legs to about 60 psi and took it for a spin around the driveway. It seemed to be working perfectly so I took it back inside, only to notice oil gushing from the right fork leg! The arch is a separate piece on these older forks, and they had separated from the lowers. There is now about a 3mm gap there. It looks like the brake boss that threads through both pieces was holding them together. I had removed these, since I'm using disc brakes. I'm going to take the fork apart, see if I can hammer the legs/arch back together, put the bosses back in, and see what happens. It seems to me that the issue with the arch separating has nothing to do with the recent air conversion, but perhaps I'm wrong. We'll see how it goes...
    Air conversion has nothing to do about that gap. You made a big mistake unscrewing the brake bosses as they hold both parts of the lowers.

    Try to put everything in place and screw the v-brake bosses ASAP.

    Buy some top caps with air valve and your old Marzocchi will be an air/coil fork.
    A pessimist is an experienced optimist

  8. #8
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    Quote Originally Posted by Pableras
    Air conversion has nothing to do about that gap. You made a big mistake unscrewing the brake bosses as they hold both parts of the lowers.

    Try to put everything in place and screw the v-brake bosses ASAP.

    Buy some top caps with air valve and your old Marzocchi will be an air/coil fork.
    Yeah, clearly. It just threw me off that I've been riding with it without the bosses for a month, and that just happened when I converted it to air. In any case, got it put back together. Just need to get some more oil, pump it up again, and hopefully it'll be good to go. Thanks again for the help.

  9. #9
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    Quote Originally Posted by willapajames
    Yeah, clearly. It just threw me off that I've been riding with it without the bosses for a month, and that just happened when I converted it to air. In any case, got it put back together. Just need to get some more oil, pump it up again, and hopefully it'll be good to go. Thanks again for the help.
    The springs weren't stiff enough for your weight, so when you put air inside at the correct pressure for your weight probably the force exerted by that air pressure was strong enough to disassemble the lowers (as the bosses were not screwed). Make sure that the fork is not leaking when you ride it (once everything is properly mounted).


    If in doubt take it to the LBS and ask the mechanic if everything is OK. Safety first

    I'm glad I helped you
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