Front Suspension

Replacing Front Fork Oil Seals

September 20, 2008

(NOTE:  September 20, 2008 was the first time that I did this job.  Since then, I have taken apart the front forks of my motorcycle, countless times!  I have replaced fork seals; slide and guide metals; installed Race Tech Emulators; modified the emulators; changed fork springs; changed fork springs again; and I have changed fork oil.  I have also custom blended my own fork oil concoction as well.  What follows below is a composite of many of those experiences; choosing a few photographs from 2008, 2010, and 2012.)

After barreling down many dirt roads inNew Brunswick, and Québec,Canada, the right fork seal finally gave out.  It began leaking oil.

In the below photograph, the classic visual symptom of a leaking oil seal, can be seen.  There is fork oil weeping out from under the seal, and spilling down the right fork tube.

And, from another time, the left fork seal leaking.

Each time I have done this job, I have chosen to replace both fork tube seals, along with the “slide” and “glide” metal bushings as well.  Probably replacing the bushings is overkill, but I figure that, since I am taking the fork tubes apart to replace the seals, I might as well replace the “slide” and “guide” metals too.

To begin this task, I “cracked” loose the left and right fork caps.  What I mean by that is, I broke the fork caps free, then slightly snugged them back up.  It is VERY difficult to loosen fork caps, once the fork tubes have been removed from the triple tree.  The triple tree acts like a vise; holding the fork tubes “sound and steady”, while the fork caps are broken free.  However, I did not want the fork caps too loose because, of the pressure the next step imparts on to the threads of the fork tubes and fork caps.


….and right.

Next, I used a screwdriver to tighten the fork pre-load adjustment screws, all the way down.  I wanted them as tight as possible.  (I will explain why I did this a little later.).

Moving down the fork, I loosened the, left and right, upper fork tube clamp bolts.

I also loosened the TOP two bolts, (left and right fork tubes), of the lower fork clamp.  But, I left the two LOWER fork clamp bolts tight.

Moving down the fork tubes a little farther, I loosened and removed the aftermarket fork brace I installed in 2007.

A little farther down the fork tubes, on the left side, I loosened and removed the brake line retainer clip…

…the speedometer electrical wire clips…..

….and, the left brake caliper.

I followed a similar, “top to bottom”, sequence on the right fork tube.

I loosened and removed the brake line distribution block bolt.

I also loosened and removed the right brake caliper.

Next, I loosened and removed the axle pinch bolt.  It is located at the bottom front area of the right fork tube.

Then, I loosened the front axle bolt.  (But, I did not remove it.).

With all of the major “tugging” completed, from loosening the above bolts, I rolled my motorcycle up on to its centerstand.  I slid a floor jack, along with a block of wood, underneath the skidplate of my bike.  I pumped the jack up enough that, the front wheel raised up off of the garage floor.  I continued raising the jack until the rear wheel touched the floor; pivoting off of the centerstand.  The bike was now stable with three points firmly on the ground; the rear wheel, and the two centerstand feet.

With the front wheel up off of the floor, and the motorcycle secure, I could drop the front wheel out from between the fork tubes.

I slipped my foot underneath the front wheel, using it to lift up the wheel assembly, (taking weight off of the axle bolt.), and then slid the axle bolt out of the fork tubes and the hub of the wheel.  The front wheel dropped free from the bike.

Next I removed the fender bolts so that I could get the fender free from the fork tubes.

Watch out for the fender bolt nuts!  Sometimes they stay with the fender, and sometimes they hit the floor, bounce and roll away to a dark corner!

Here is the fender clear of the fork tubes.

The next two bolts that I needed to loosen were the, damper rod bolts.  They hold the oil lock piece, and the damper rods in place.  In the second step of this maintenance task, I tightened the fork spring pre-load, all the way down.  The reason I did this was, to place as much tension as I could, on to the damper rods.  The damper rods are located at the bottom of each fork tube.  Sometimes, if there is enough tension from the fork springs, bearing down on the damper rods, the rods won’t spin in the fork tube, while you are trying to loosen the damper rod bolts.

However, if the damper rods do spin, I have found no other way to loosen the bolts, other then using a pneumatic impact driver.  A short pull of the impact driver’s trigger, imparts the quick “energy” needed to break the damper rod bolt free from the damper rod.  Possibly, a battery powered “hammer drill” would also do the trick as well.

To keep the lower portion of the fork tubes from spinning, (the portion of the fork tube that the damper rods are bolted to.), I slid a “star drill” I had on hand, through a brake caliper bolt hole, on each fork tube.  It was the only thing that I had that was long enough, and slim enough to pass through the caliper bolt holes!

Using my impact wrench, with a 6mm, “impact style”, Allen wrench attached to it, I gave a quick, short “burst” with the trigger.  The idea here was to just break the bolt free, but not loosen it all the way.  If I did, fork oil would start pouring out of the bottom of the fork tube!  (I learn most things the hard way……..).  The idea here was to treat the damper rod bolt, just like I did the fork cap; break the bolt free, but snug it back up, so that oil won’t leak out.

Then, I moved to the middle of the fork tubes, and I loosened the lower, fork tube clamp, bolt.  I did this last loosening, one fork tube at a time. Again, I have learned the hard way; once that lower fork clamp bolt is loose, the fork tube wants to slide out quickly!

[Note: This next step is important!]

With a fork tube free, I completely backed off all pre-load tension that I had applied, with a screwdriver.  I did this because, the following step is to remove the fork cap.  I want ALL tension off of the fork cap as I spin it free from the fork tube!

Then, I dumped out the fork oil.  When the fork oil is fairly old, and “used” up, I will dump it into a storage container.  I can then dispose of the oil properly at a later date.

When the fork oil is still fairly new, I will dump it into a clean container that will allow me to reuse it.

As I dump the oil, “pieces and parts” will want to tumble out of the fork tube, along with the oil.  The spring spacer, spring / spacer washer, and fork spring will all want to slide out of the tube.  In my fork configuration, I also have to watch for the Race Tech emulators tumbling out of the fork too.

In next photograph, I have “pumped” the fork tube, several times, to force more fork oil up and out of the damper rod assembly.  If the fork tube is not pumped, residual fork oil is left in the bottom of the tube.  When the damper rod bolt is removed, excess fork oil will spill all over the place.  (Like I said, I learn things the hard way!).

I use a very deliberate motion of compressing all the way, and extending fully, the fork tube assembly.  It takes about three to four, “compressions” and “extensions”, to “burp” the remaining fork oil out of the tube.  As I do this, I keep the open end of the fork tube over the catch container.  That way, I can collect the rest of the fork oil that will be pumped out of the fork tube.

In the previous photograph, while pumping the last bit of fork oil out of the fork tube, you can see the, fork spring spacer, the spring / spacer washer, and the spring from the tube, “draining” excess oil, in an old bread pan, along with the fork cap.

Once the fork oil, and the “loose parts” are out of the fork tube, I can then remove the damper rod from the fork cylinder.

I inserted a 6mm Allen wrench into the bottom of the fork cylinder……

…and removed the damper rod bolt.

At this point, I can tilt the top of the fork tube downward, give it a little shake, and the damper rod will slide down and out of the tube.

The photograph below, illustrates the internal parts of my fork tubes.

From the bottom left, moving to the right: Damper rod; a Race Tech Emulator sits on top of the damper rod; the fork spring sits on top of the emulator; the spacer washer sits on top of the fork spring, (I use two fork spring / spacer washers.  No particular reason!); the spacer; and the fork cap.

Here is a schematic diagram of what the complete assembly looks like.

Once the “guts” of the fork tube were removed, I could begin the process of separating the fork tube from the fork cylinder.

Using a screwdriver, I pried up the dust seal, and slid it up and off of the fork tube.

Looking down into the fork cylinder, there is a seal “stopper ring” that needs to be removed.  Here again, I used a screwdriver to pry the “stopper ring” free from its groove, and up and out of the fork cylinder.

At this point, the fork tube can be separated from the fork cylinder.  To do this, I grab the fork cylinder in one hand, (the bottom end of the fork assembly), and I grab the fork tube with my other hand, (the silver, “working portion” of the fork assembly), and I give a couple of very sharps tugs; pulling the cylinder and tube apart from each other.

Below is a photograph of the fork tube separated from the fork cylinder.  I turned the “guide metal” sideways in the fork cylinder so that it can be seen clearer.  On the fork tube is the, “slide metal”, the seal spacer, and the seal.

I slid the oil seal, and the spacer, (looks like a big washer), off of the fork tube.  I used a screwdriver to pry the “slide metal” off of the fork tube.

I installed a new OEM “slide metal” bushing on to the end of the fork tube.

I slid the “oil lock piece” into the fork cylinder and tilted the cylinder up, so that the “oil lock piece” would slide to the bottom of the fork cylinder.

Using a finger, I coated the “slide metal” with a film of fork oil.  I then carefully slid the fork tube back into the cylinder, and down on top of the Oil Lock Piece.

Next, I put a thin coat of fork oil on the inside of the of the fork cylinder, where the Guide Bushing gets installed. I started the Guide Bushing into its slot, then used the metal spacer, (“The Big Washer”), to “set” the Guide Bushing home; lightly tapping the the Guide Bushing in place using a hammer and the metal spacer.

After the fork tube and fork cylinder were back together, I slid the damper rod down the fork tube.  I didn’t just drop it down the tube, as could be inferred from the photograph below.  I tilted the fork assembly so that the damper rod would slide down gently.

When the damper rod was in the bottom of the tube, I added a new “crush washer” to the damper rod bolt, and I installed the bolt into the bottom of the fork cylinder; tightening it as much as I could.  Once the fork tube assembly is clamped back into the triple trees, I can properly torque the damper bolt to the proper specification. called out for in the Suzuki Service Manual.

Next, with the fork tube compressed into the fork cylinder, I slid the oil seal spacer over the fork tube and down into the fork cylinder.

After that, I slid a new oil seal over the fork tube, and pushed it down, as far as I could towards the fork cylinder.  The side of the seal that needs to face “downward” is the open side; the side where the “spring” can be seen inside of the seal.

I used a screwdriver to gently “nudge” the seal a little closer to home.

The next step is to “set” the seal.  Some riders have used a piece of PVC pipe, of a diameter that will slide down over the fork tube, and bear against the seal.  They will “tap” the end of the PVC pipe, with a hammer, to set the seal into the neck of the fork cylinder.

When I did this job, I did not have a piece of PVC pipe on hand.  Nor, did I have access to a vehicle to go purchase some!  So, I cut a wooden wedge to do the job.  I tapped the end of the wedge; working it around the seal, so that the oil seal would be evenly pressed into the fork cylinder.

When the seal was set in place, I added the seal retaining ring on top of it, and I also slid the dust cover into place too.

It was now time to refill the fork tube with fork oil.  Before I did so, I slid the Race Tech Emulator down the fork tube, and made sure that it was sitting on top of the damper rod.

[Note:  The next step is important.]

Then, I poured some fork oil into the fork cylinder.  Not all of it, though. I poured just enough so that I could pump the fork assembly; “sucking” fork oil down into the damper rod area.  It usually takes about three, or four, really good “pumps” to be able to feel the hydraulic resistance of the damper rod valve system.

Once the air had been pumped out of the bottom of the damper system, I began the process of filling the fork tube with fork oil.  The first thing I needed to do was to make sure that the fork assembly was standing, “plumb” and vertical.  The fork tube needed to be fully compressed into the fork cylinder.

I like to have an air space, over the fork oil, of 150mm.  That measurement is from the top edge of the of the compressed fork tube, and down to the top of the fork oil.  So, I intentionally overfill the fork tube with fork oil.  With a “turkey baster” I suck out the excess fork oil; bringing the level down to the 150mm mark.

If you look at the photograph below, the bottom edge of the piece of blue tape, wrapped around the turkey baster, is 150mm up from the turkey baster’s tip.  To remove the excess fork oil, I slide the turkey baster down the fork tube, until the bottom edge of the tape comes in contact with the top edge of the fork tube.  I squeeze the “bulb” of the turkey baster and remove the excess fork oil, until I can’t pick up anymore.

When I have enough fork oil in the fork tube, I slide the fork spring in place; down the fork tube.  I will add the spring / spacer washer next.  Then, I will extend the fork tube out as far as it will go.  I will slide the spacer in next.  Finally, I will CAREFULLY compress the “guts” of the fork tube, with the fork cap, and tighten it down.

To tighten the fork cap, down into the fork tube, I will hold the bottom portion of the fork assembly between my feet.  I will also “clamp” my knees to the works too.  Using my left hand, I pull “upward” on the fork tube, and using my right hand, I press “downward” with the fork cap; slowly and carefully threading the cap into the fork tube.  I DO NOT try to tighten the fork cap completely at this point.  I do that once the fork assembly is clamped back down into the bike’s triple tree.

From here the assembly is reverse of disassembly.  I slid the fork tube up into the triple tree.  I snugged up the bottom bolt of the lower fork clamp.  Then, I snugged up the top fork clamp bolt, then back down to the top fork clamp bolt of the lower fork clamp.

I torqued the upper fork clamp bolt to the Service Manual’s specification.  I did the same to the lower two bolts as well.  Here is a secret about this though.  When I torque the two bolts, of the lower fork clamp, I do so by tightening them “back and forth”.  What I mean by that is, I tighten the top bolt, then the bottom bolt, then the top bolt again, then the bottom bolt again.  You see, as one bolt is tightened, then its “brother” next to it, (the first bolt), becomes loose again.  Both of the lower fork clamp bolts must be tightened in this manner; first one, then the other, then back to the first one, then back to the second one.

Finally, I torqued the damper rod bolt at the bottom of the fork assembly, than tightened down the fork cap at the top of the fork assembly.  Using a screwdriver, I adjusted my spring pre-load where I like it.

Then, I started on the other fork tube……..

As a final note to this article, I weigh about 185lbs with all of my riding gear on.  I categorize myself as an aggressive rider, and I like to ride rough roads.  The best front suspension configuration that I have found for me is; stock Suzuki fork springs, 10 weight fork oil, with a 150mm air space over the oil.  I have Race Tech Gold Valve Emulators installed as well.  These emulators have the stock “yellow”, pre-load spring adjusted to just “one turn”.  I have modified the top plate of the emulator by drilling four 1/8”diameter holes through it.  All of this works perfectly for my riding style, and riding conditions!

Categories: Front Suspension | 23 Comments

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