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Yestertech Weekly #7

The Attic - Yestertech Weekly

Enduro Mag 21 Seals
Let me preface this by saying that the entire overhaul comes down to having a few special tools...  The Rock Shox Mag series busing puller, stanchion vice blocks and a seal press.  Without these tools you should not attempt an overhaul.  Bring the fork to your Local Bike Shop or send it to our friend B Rose at Shockspital

Rock Shox Mag Tools
So you think you need an overhaul....  The Mag forks tended to need servicing periodically to keep them running smooth.  The forks where not sealed as well as most of the newer forks and if you rode in wet areas the oil in your fork would contaminate quickly.   So if you haven't changed the oil in a while and you are still riding a Mag series fork you are due for an overhaul.   If you see oil leaking from the fork leg around the seal...  You are due for an overhaul.   If you fork does not hold air....  You are in need of work but the Enduro seals are not going to help.  The Enduro seals seal the oil in the fork.  There is another seal at the top cap that seals in the air.   This seal is not currently available and may render your fork unrideable.    Before you throw it in the used parts bin drop Bikeman or Shockspital an email and see if we can help you out. 

Enduro Seals Retro Overhaul
On to the overhaul.   The first step is to take remove the fork legs from the crown.  By un bolting the fork brace and loosening the bolts on the crown you can remove each leg from the bike.   This makes it very easy to work on the fork legs.  So why don't current forks use this system you might ask.   Well anything bolted is inherently going to flex more.   This was not a stiff fork by any means and even with an aftermarket fork brace would still flex more than any fork on the market today.    I will take a stiffer fork in a high speed corner over ease of servicing any day.

Remove the Dust Seal
After the fork leg is removed from the bike you will need to pry up the dust seal.   The Mag forks had a dust seal that is visible at the top of the lower leg.  This can be carefully pried up with a small flat head screw driver.  Work around the fork slowly as we will need to reuse this seal.  Once you have the dust seal off you will be able to see the main seal in the lower leg with a Snap Ring holding it in place.   You will need a set of Internal Snap Ring Pliers to get the ring out.  

Remove the Air
Next you will need to remove the air from the fork.  Most of the new Mag forks will have an opening at the top where you will put in a Rock Shox needle to let out the air.  It may look like a standard basketball needle, and a regular ball needle will work if need be, but the Rock Shox Mag needle only has a hole at the bottom and not on the side.   The problem with the needles having a hole on the side is that they can tear the seal on the way out.  So a regular needle will work but throw some spit on it and be careful.  


Remove the Top Cap
With the air out of the fork you can take the top cap off and drain the oil.  The top cap will either be use 19mm wrench (1993 and older forks) or a 22mm wrench (1994 and older forks) for removal.  Be careful to no round off the edges.  Cycling the fork up and down will help get most of the oil out of the fork.  Take note of how the oil looks.  If it is gray or milky looking your fork oil has been contaminated.  It should be clear when it is clean.  Now it is time to use the fun tools..

Mag Fork Tools In Place
The Rock Shox Mag 21 Seal puller and vice blocks are necessary to properly remove your fork seals.  With the air out of the fork extend the leg as far as you can and slide the seal puller onto the fork.  Thread the puller together till you have room to put the upper tube vice block onto the end of the fork.  Now you can clamp the vice blocks, with fork attached, into your bench vice.  You are all set to pull the seals.  You should be able to thread the tool appart with your hand.  If not, on the seal puller there are two wrench flats that will accept a 36and 32mm headset wrenchs.  Put one on each of the flats and start Mag Tools in Actionthreading the puller apart.  There is a small window cut out on the puller that will allow you to see the progress of the seal as it is pulled form the fork.  When you see the seal in the window your fork tubes have been separated and you can remove the leg from the vice.

Everything will slide appart smoothly and you can see how simple this fork really is.  Carefully clean the bushings, springs and legs to get as much of the contaminated oil off the fork.  You should also clean out the lower leg as it may also contain some contaminated oil.  After you are satisfied with the fork being clean it is time to prep for reassembly.  Using your choice fork oil, somewhere between a 5 and 10 weight fork oil, lightly coat the upper leg with oil.  Reassemble the inners as they came out of the fork and slide on a fresh Enduro Seal.  You do not need to put any oil on the seal itself. 

Once the inner leg is assembled you can slide it into the lower leg.  Once everything is set in place you can slide the seal press over the inner leg and carefully / evenly press the seal into place.  It should seat all the way down into the lower leg so that you can install the Snap Ring.  So that is the next step.  Install your Snap Ring using your Internal Snap Ring Pliers.  Do not assemble the dust seal just yet.   We want to be able to check the fork seal after the fork has been pressurized. 

Make sure the oil damper adjusting rod is turned to full counterclockwise position, using an aircap or an old adjuster head.   Begin adding oil to the top of the tube.  Slowly pump upper tube up and down fully until no air pockets are felt in the damping and then continue to add or remove some oil to get approximately 1.5 - 2cm of space between the top of the tube and the oil, when the tube is completely compressed.   You can now proceed to install the top cap and pressurize the fork to 100PSI for an hour.   Pressurizing the fork to 100PSI will make sure everything is set and ready to go.   After an hour you can drop the pressure to between 40 and 55PSI.  You can vary on this to get the ride performance you are looking for. 

Rock Shox Mag 21 Forks


The Mag forks are close to infinitely adjustable.  Here is a blurb right out of a Rock Shox service manual about the effects of adjustments on the fork.  We are hoping to have a PDF manual online next week for your review. 

Rock Shox:  "The air spring of the ROCK SHOX MAG series forks works by compressing a volume of air. As the air compresses, the pressure rises, causing more force to be exerted against tubes. This force creates a progressive spring curve that resists bottoming. Changing the space of air inside the fork dramatically alters the spring curve. Since oil is non-compressible, the level of oil inside the fork can be set to create the optimal spring curve. The oil level is measured, rather than volume, to create the proper air space and spring curve. Changing fork oil viscosity will change the damping of the fork. A lower viscosity fork oil allows the fork to compress and rebound faster. RockShox 5 weight Racing Oil is recommended for most riders. Heavier riders (>180 pounds) may prefer the performance of RockShox 8 weight Racing oil, because larger compression and rebound forces will be generated and require higher damping"


Enjoy your Enduro seals and please let us know if you have any questions.  If the repair sounds like it is over your head or you do not have the proper tools....  Drop by your LBS and ask them about an overhaul or drop in on Shockspital for a professional repair. 



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