I rewrote this to be more clear. First is background and last is the fork oil change procedure. Closed-Cartridge Forks - Poor & Contradictory Tech Info I found little (and contradictory) tech info regarding closed cartridge forks on trials bikes. There is much more available info on closed-cartridge USD forks for other bikes on YouTube. Anyway, here is exploded view of the Marzocchi aluminum-stanchion trials forks: In the exploded view all the parts are exploded, including caps, etc. In my descriptions below the parts are in described as subassemblies. The aluminum-stanchion closed-cartridge Marzocchi forks are quite common on many later-model trials bikes. These typically have a black coating on the aluminum tubes and various paint colors on the cast aluminum legs or sliders. Most common is white. These forks predominate the GasGas trials bike up to present (2014). The exceptions are Eco with Olle R16V forks and shocks, and the Replicas with Tech forks. The new Ossas use the Marzocchis. I have a `10 Econo 280 that has Sachs forks with black diamond coated steel stanchions and cast aluminum sliders that are also closed cartridge. And what is "closed cartridge?" Forks were long damper rod based. Oil was simply squeezed through orifices in compression and rebound. Later came cartridge forks where the damping was done inside cartridges with rods attached to the fork caps. A more recent innovation was the so-called closed-cartridge forks. The previous cartridges were then called 'open', that is, they exchanged a significant volume of oil with the surrounding reservoir at each stroke, being 'pump-through' designs, pulling oil from the surrounding reservoir and dumping that oil back to the reservoir from the caps. Closed cartridges are not truly closed. They still exchange oil from the surrounding reservoir, but they exchange little oil per stroke. They require a special bleeding procedure if you disassemble them or unwittingly pump the oil out of them during an oil change. My unpleasant intro to the closed-cartridge designs was doing maintenance on my `10 Econo's Sachs forks. I dutifully pumped the rebound cartridge out as one might do with open cartridge forks to get rid of the old oil in them. That took some effort, and I was rewarded with a Homer doh! forehead smack. I refilled the fork then could not get the cartridge to pump back up as expected. Off to the web I went to find complaints of no damping by riders after fork oil changes. I also found little or just crap info about bleeding procedures. It took about 10 hours of riding time for the rebound cartridge to finally exchange enough oil to de-air itself. This experience made me averse to changing oil in the Marzocchi forks, which I knew are also closed cartridge designs. Then it dawned on me while riding at Sipapu - one of those eyelid movies that play on the loop (for engineer types anyway) - that I could simply step around the hassle by changing only the oil bath around the cartridge, which is the majority of the volume of the oil, and that I could exchange all the oil by doing the simpler oil change more than once, avoiding any special bleeding procedure. If any of you have found a well-written bleeding procedure for closed cartridge forks, please post that here, as some of us may some day have to disassemble the forks. I have one I translated from an Italian guy who said he worked for Marzocchi, but I could not get it beyond a garbled mess. My `11 Raga Marzocchis I needed to do maintenance after a year of competition to keep the metal particulates count down, and I wished to change the oil as my forks have long been on the too-sat side, and I ended up dialing the adjusters near all the way in. The previous oil change was about 2012 by the former owner, who reported a big hassle because he was curious abou the cartridges and disassembled them. He was used to open-catridge forks and could not get them to pump up, so he disassembled them again thinking he had made some mistake. Many frustrated hours later, he learned there was some special procedure for bleeding them, but could not find it. I'm not sure how he got them to bleed, maybe just by riging the bike a while. The former owner said made up some of the recommended 7.5 weight oil by mixing half Redline synthetic 5 with half Redline synthetic 10 (they don't have a 7.5). I'd checked the oil after I got the bike. It was set to about 6.25" height (I later set mine at 6.00"), and it looked clean, so I just stuck with that oil until now. Yesterday I did the maintenance . Experience showed I needed a slightly thicker oil to bring the adjusters back to the mid range of clicks. That proved to be a right guess. I had on hand some Maxima Racing Fork Fluid, their top high-performance stuff. Maxima actually provides the oil viscosity as 165 SUS (Saybolt Universal Seconds) and equated with SAE 10 weight. Most oil retailer list their oils in SAE weights, which is not an accurate way to describe viscosity. I don't know what Redline 7.5 is in SUS, but I can tell you it is too thin. If you use Redline, which is a really top oil, use their 10 weight. Here is the web link to Maxima Racing fork fluid: http://www.maximausa.com/product/racing-fork-fluid/ Also listed on the Maxima oil is the viscosity index or VI 150. Thus the oil I used is labeled as "165-150 SUS-VI" Viscosity index, the second number, is the measure of an oil's resistance to changing viscosity with temperature changes. A higher number is better, and the synthetics are tops in this category. Anyway, it was a very good oil I used. Had I had Redline in 10 weight, I'd've been happy to use that as well, but because they don't list the viscosity, how thick is it at a given temperature, really? Another aggravation I found is the web and the tech info is confused regarding the recommended oil height. Oil height is the best way to deal with forks. The oil-height spec is actually the depth from the top of the stanchion to the oil when the forks are fully bled, collapsed and the springs are out. Changing fork oil only by volume is a bad idea because it is not accurate. You can end up with too much or too little oil. As long as you have enough oil it won't affect the damping at all, but it will affect what can feel like damping at end of travel: the secondary air spring, the stiffness of which is determined by the size of the air bubble trapped in the fork above the oil level. With the springs in, the air bubble is pretty small and the pressure inside spikes way up when the forks are bottomed. Too much oil can lead to solid bottoming before end of travel (massive pressure spike). Too little oil can lead to too weak a secondary spring for harsher bottoming, and if there is way too little oil you can suck air into the cartridges for sketchy damping. The only way to know for sure what you have in there is to measure by the "height spec." I use a flashlight to see in there and a wire that goes down and touches the oil to find the level. On my Marzocchis, I bent wire 90 degrees at 6" and made the settled oil just touch the wire when it rest on the top edge of the stanchion. Some use fancy tools to suck out oil to a specific level, but I don't have one of those. So what is the Marzocchi height supposed to be? I found 180mm, then 160mm, and also 140mm. I think 180mm will have too much air and too soft a secondary air spring will be too soft. At 140mm the volume of trapped air may be too small. I opted for 152mm (6.00") and that is working as it should. A long test ride at the middle temperature of 70 degrees showed the forks to be working as they should. Controlled, but I could still hop with ease. The adjusters settled into 16 of 26 of a total of clicks in, which is on the slow side of the mid point. The Maxima '10 weight' oil is definitely confirmed as right and not too thick and it gives me a wide rancge of clicks for extreme temperatures compensation. My Simplified Maintenance Procedure Both Marzocchi forks are similar in build though the right side fork has rebound damping with an adjuster, and the left side has the compression damping with an adjuster. I suspect both sides share some rebound and compression resistance as these forks have a spring in both sides as opposed to previous forks with a spring only in the compression side to balance the spring and damping forces. On the rebound side when you remove the cap a long rod with o-ring at the end will pull out of the cartridge rod. The compression adjuster screw stays with the cartridge rod on the compression side. I pressure wash my bike first and hit the front end good with plastic covers and fender removed. I don't worry about nuking the hubs because I pop off the wheel bearing seals and blow out the old grease and re pack the wheel bearings completely full. Make sure you used brake cleaner on and wipe you brake disk to make sure you do not have any oil or grease on the disk! After you clean things up, ride the bike somewhere clean and bounce the front end hard to stir up the typical grey metallic sludge that will settle on the bottom insides of the fork when the bike is stored. Obviously it is better to change fork oils when the forks aren't freezing cold. Before you remove the forks, loosen the top triple clamp screws and loosen the caps. Someone in the past may have thought these must assembled bone dry then gorilla tightened (argh!). I never torque fork caps! I just grease the threads and O-rings and just touch them to the stanchions. They seal by the o-rings and never unscrew! My oil change procedure does not require disassembling the fork, only the removal of the caps, preload spacers, and springs. You need to have the springs and preload space out to accurately measure the oil level, which is always done springs out and everything fully collapsed. Also, I typically hold my forks in a vice with a sock around the sliders to prevent scratches to the pain. Another helpful detail regards access to the aluminum cap retaining nut to remove the cap when the preload spacer and spring are still in place: Simply compress the spring by pulling the preload spacer down, then cock it under the cap retaining nut (part #24 in the exploded view). That frees both your hands to use two wrenches to remove the caps. The trick around special bleeding procedures on closed-cartridge forks is to avoid stroking the cartridge rods any more than barely pulling them up when there is little or no oil in the reservoir around the cartridges, such as after you dump the oil out. I collapse the forks and push the cartridge rods in, then tilt the forks and pour out the oil, observe how dirty it is. I refill the forks with the oil, the same oil I intend to end up using. I overfill them a bit then pull the rod up a bit and hand tighten the caps back onto the cartridge rods without the springs. I extend the forks fully slowly then screw on the caps until the sealing o-ring just passes inside the stanchions. Then I stroke the heck out of the forks against the floor using the trapped air as a return spring. Stroke, slosh, and dump the oil, observing again how clean it is. Repeat until very clean. It's more expensive to use fork oil instead of, say, a kerosene flush, but because of the closed cartridges you must use new fork oil as a flushing agent. My oil was clean enough that I only had to bench flush twice to have clean oil. If your oil is really trashed, and it is cleaning up well but not completely, given this procedure is simple, imperfect oil is better than trashed oil. Ride the bike a while to fully exchange the oil in the cartridges and later do the above again. Once you get the oil cleaned up, you should be able to do maintenance every year or two with just the above procedure. A plus about these forks is they come with great seals. I have seen forks with many impact damaged stanchions that have been smoothed and filled with fingernail polish and don't leak. I have three very slight small damaged areas and no leaks. Whatever they coat the aluminum stanchions with is pretty amazing stuff. I found the substance will smear up onto damaged areas and provide protection. I hope this has helped simplify the mysteries of these forks. If I missed something, please chime in.