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Fork Seals: A quick how to ('99 FZX250 Zeal)

Discussion in 'Tech Help' started by Kyle, Jul 18, 2014.

  1. Kyle
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    Kyle RubberMan™

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    Replaced the fork seals in Jadey's bike today, thought I might post up a quick how to in case anyone else wants to tackle this job themselves and save a couple of hundred dollars (quoted $300 to get someone to do the job, paid $20 at the hardware store for pieces that can be re-used as tools, $20 for fork oil and $35 for seals). It isn't overly difficult (if you can perform basic maintenance, this won't be a stretch) it just takes a bit of time :)

    Usually, fork seals are only replaced when they start to leak or split. If you notice fork oil on the exterior of the forks (you can touch or see it), it is time to inspect the seals. Run a business card or film negative around the fork seals (you'll have to lift the dust cover, this is the seal that you can see) to remove any debris, as most of the time the fork seals are fine, just fouled. If you still are getting oil on the outside of the fork, stop riding the bike, as not only will you cause undue wear on the suspension and risk its failure, the fork oil will also drip onto the brakes and cause them to seize. (not fun.)

    Obviously this will be quite specific to the bike I was working on ('99 FZX250 Zeal), but the process can be applied to all upright fork bikes. You need to stand on your head and follow the instructions backwards for upside down forks.

    What you will need:
    Socket set and spanners (sizes from 12mm to 19mm)
    Pliers/mole grips
    Clamp (optional, but handy)
    Fork seals and oil to match your bike (check the manual for what weight fork oil you'll need, this bike was a 10W)
    Small flat head screwdriver
    3ft 5/8 threaded rod and 4 5/8-11 nuts (from hardware store for about $12)
    PVC pipe with a 1 or 2 mm more internal diameter than the outer diameter of your upper fork tube (I used 40mm in this case) OR a fork seal tool. One of these tools for these forks is $70, the PVC pipe was $7...
    Some electrical tape.
    Towel/rags
    Parts cleaner
    Patience.
    More patience.
    Coffee and/or beer.

    Step 1: Unassembly

    First, lift the bike from the underbelly the get the front wheel in the air. If you have a bike cradle (or sturdy crossbeam in the roof etc.) you can hoist the bike up from the triple tree. I took the pipes off of the Zeal so that I could lift it squarely from the underside of the engine, do whatever works for you. I've simply used a dirtbike lift and two sandbags to stabilise the bike whilst I shake it to undo things and bump into it as I grab tools.

    [​IMG]

    Next, remove the wheel, brake(s) and fairing, as well as any accessories or indicators attached to the fork tubes, so that you have the forks sitting in the lower and upper clamp. I have zip tied the brake assembly to the frame so that it is not hanging from the brake line.

    [​IMG]

    Next, crack the nut at the top of the fork assembly (much easier when it is still on the bike rather than a stand alone fork...)

    Then undo the bolt on the top and lower clamp that holds one of the forks in place. Slide the fork out towards the floor (ensure you have the bike raised high enough) and then place it in a vice or on a table or towel. In this how to, I will refer to the skinnier section of the forks as either the upper fork tube (as it is the top of the fork assembly) or the inner fork tube (as it goes inside the other piece), and the thicker fork tube that attaches to the wheel as the lower fork tube or outer fork tube.

    [​IMG]

    Undo the top nut fully and remove the cover, ensure to be careful as this is under spring tension. Fork oil will also follow if the fork is on its side, so either stand the fork up or put a drip tray under the end.

    [​IMG]

    The metal tube hanging out is the collar, it sits on top of the spring and keeps it under tension. Careful when you remove it, there will be a spring seat between the collar and spring, which is essentially a washer to keep the two separated. Try not to drop it in the oil!

    [​IMG]

    Next, remove the spring and drain all the fork oil out you can by tipping the fork upside down. Next, you'll need a tool to hold the dampener still whilst you undo the bolt at the bottom of the forks that holds the assembly together. I used a 5/8 threaded rod that was about 3ft long (you could easily get away with a 50-60cm one if you wished, it was just sold by the metre) and secured two 5/8-11 nuts to the top and bottom by tightening them together. This provides a point to grip with your locking pliers at one end, and a bolt to fit into/apply pressure to the top of the dampener on the other to prevent it from spinning.

    [​IMG]

    Next, slide the above tool down the upper fork tube, and push in place against the dampener (you haven't seen this piece yet, it is still inside the suspension and holding the upper and lower fork tube together). Place an Allen key in the bottom of the fork, and undo. This will be very tight, it took another set of locking pliers to apply enough leverage to get it undone. Ensure you hold your dampener tool firmly against the inside of the tubes so as to prevent the dampener from spinning as you undo the bolt.

    [​IMG]

    Next, slowly tip up the forks and allow the dampener and its spring to come out of the top of the forks. Then, secure the forks the right way up and use a small screwdriver to lever the dust cover away from the fork.

    [​IMG]

    Next, unclip and remove the snap ring that you have exposed from under the dust cover by using the screwdriver to pry the clip from the recess. Then, firmly tug the upper fork tube away from the lower fork tube. It will take a few goes, and a a medium amount of pressure, to get the two to separate. You are unseating the bearings by doing this, and will allow access to the fork seal. Next line all the parts up on a towel so that you are sure of the order to put the pieces back together, and can give them all a clean using parts cleaner. Get rid of any dirt and old fork oil, this will reduce the friction once you reassemble the forks and prolong the life of the seals and fork internals.

    [​IMG]

    A breakdown of the parts (stolen from a how to website on an FZR600, same internal as this bike for the forks)

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Part 2: Replace the fork seal and reassemble

    If you are so inclined, check the manual or online to find out the torque settings for each of the bolts and use a torque wrench, if you can handle your friends laughing at you. Otherwise, ensure you do not over tighten anything, make sure you tighten things so that they wont fall off, and try to get the bit as tight as it was when you removed it...

    Slide the dampener spring back onto the dampener, and place the dampener into the upper fork tube (as in the diagram above). Slide this assembly back into the lower fork tube, ensuring that the bearings are back in accordance with the above pictures. Use the dampener tool to hold the dampener in place, and re-tighten the bolt back into the bottom of the fork.

    Next, secure the fork upright. If you have a fork seal tool, get that, otherwise your PVC pipe acquired to fit the upper tube. Ensure that the bottom of the pipe does not come to a sharp point (and thus damage the fork seals), and wrap some electrical tape around the edges of the pipe.

    Look down at where the upper and lower fork join, and notice that the bearing is sitting above the seat of the upper tube. Slide the fork seal tool or PVC pipe over the upper tube, and either raise and drop this to hammer the bearing flush with the seat, or tap the top of the pipe with some wood or a hammer.

    [​IMG]

    Next, place the washer over the upper fork and cover the bearing. Ensure you do not get any dirt or grit in here.

    [​IMG]

    Next, rub some oil over the fork seal, and slide this over the upper fork. The seal should have the "nipple" and the serial numbers facing up. Repeat the process with the PVC or fork seal tool to drive the fork seal into place. You should be able to see the recess that the snap ring came out of.

    [​IMG]

    Next, replace the snap ring ensuring that it sits in the recess, and replace the dust cover. Now, secure the pipe upright and ensure that the upper fork can move smoothly within the lower fork. If not, you have over tightened the bearing or fork seal, and will need to unassemble the forks as before and try again. Next, check in the manual how much fork oil to use, and top up the fork oil from the top of the upper tube. Ensure that you have not replaced the spring, spring seat or collar, and that the forks are in the fully compressed (or lowered) position. For this bike, it takes approximately 370ml of fork oil, which is the tube filled to 11.1 cm below the top of the upper fork tube. I used a ruler and some masking tape to mark where the oil level was. Next, replace the spring, spring seat and collar, then extend the upper tube as high as it goes. Now, use the cap to push down on the collar, and tighten by hand. Once it is threaded and will hold in the spring, tighten with a socket or spanner, and remount on the bike.

    [​IMG]

    Step 3: Do it all again

    The bad news is you've finished one of the forks, but the great news is it was so much fun you get to do it again on the other fork! Take this fork out and repeat steps 1 and 2. Then, ensure both forks are remounted at the correct height and reassemble the wheel, brake(s) and fairing. And you're done!

    [​IMG]
     
    Last edited: Jul 18, 2014
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  2. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    Nice, adds a bit of detail to the slightly older school forks I refreshed and chucked in a Wiki article here.
     
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  3. adrian1
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    adrian1 Member

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    Good write up! If you buy cheap seals make sure they are the same thickness as OEM! Been there :62.gif:

    Bunnings sell the threaded rod

    Insert expletives when trying to get fork cap back on again!

    Leave all axle nuts loose and bounce forks to align the whole show before tightening. Then double check you HAVE tightened the axle nut etc!
     
    Last edited: Jul 19, 2014
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  4. Frosty
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    Frosty Member

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    Nice write up Kyle, now come and put the correct weighted springs in my KTM forks for free please :p
     
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  5. Kyle
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    Kyle RubberMan™

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    Only if I get a glass of water this time ;)
     
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