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How-To: Fork spring replacement & Fork oil change

Started by Alphamazing, April 17, 2006, 03:05:03 PM

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Alphamazing

This is a very simple procedure that isn't very well described in the Clymer manual. My intention is so that even the most mechanically uninclined can follow it and do this procedure.
Please read this in full before beginning your work.

This was performed on a 2004 GS500 without fairings. F models may require lower fairing removal.

Tools & Supplies Needed
8mm, 10mm, 14mm, 17mm wrenches
19mm wrench or 1/2" drive socket wrench depending on year (for the fork caps. Find out which you need before beginning your work)
3mm, 4mm, 6mm allen head (hex head) wrenches
pliers
oil pan
hack saw
file
pencil
tape measure
measuring cup
fork oil, replacement springs, spacer material
assorted 2x4s or a bike jack
friend (helpful!)

Start with the bike on the centerstand.

Step 1 - Bar removal/Loosening the fork caps
Using the 19mm wrench, break loose the fork caps. It is easiest to do it now rather than struggling with them off the bike. If you have lower bars (Suburban Machinery, for example), use the 6mm allen wrench to remove the bar clamps so that you can move the bars in order to gain access to the fork caps.

Step 2 - Loosening the axle nut
Using the pliers, pull out the cotter pin on the front axle nut. Now using the 19mm wrench on the castle nut and the 17mm wrench on the axle bolt break loose the castle nut.

Step 3 - Supporting the bike
Place 2x4s underneath the bike or use a bike jack so that the front wheel is off the ground. It is okay to place the 2x4s under the exhaust to support the bike.

Step 4 - Brake caliper removal
Using the 14mm wrench, remove the bolts holding the brake caliper and remove it from the brake disc. You can allow it to hang from the line or secure it to the frame in some manner. I set mine on my case guards.

Step 5 - Wheel removal
Using the 19mm wrench, finish taking the castle nut off the front axle. Push the axle out of the front wheel and remove the front wheel. To keep things neat I put the axle back through the wheel and re-thread the castle nut a few turns.

Step 6 - Fender and fork brace
Using the 8mm wrench (I found it best to use a socket with an extension) and the 3mm allen wrench, remove the nuts from underneath the front fender. There are four sets of these nuts, washers, and bolts holding the front fender to the fork brace. Pull the front fender down and out of the forks and set aside. Use the 4mm allen wrench to remove the four bolts holding he fork brace to the forks. Use the 10mm wrench to remove the speedometer cable guide wire from the lower left fork leg.

Step 7 - Pinch bolts
Using the 6mm allen wrench loosen the pinch bolts on the upper triple clamp holding the forks. Do not remove the bolts, but make sure they are loose. Next, with the 14mm wrench, loosen the pinch bolts on the lower triple clamp. Again, do not remove them but make sure they are loose.

Step 8 - Fork removal
Pull the forks out of the triple clamps using a twisting motion to help ease them out. They should slide out fairly easily and through the headlight brackets without much hesitation.

Step 9 - Uncapping the forks
Using the 19mm wrench remove the fork cap off one fork. BE CAREFUL! The spring is under preload and can op out with a fair amoutn of force. Pull the spacer out and pour the used fork oil into the oil pan. Be sure to catch the washer and spring as they come out! Fishing them out of the oil is not fun. Continue letting the fork oil drip into the pan. Pump the fork a few times to aid in removing the oil. For those who are anal retentive (or "thorough"), suspend the fork upside down over the oil pan to allow the oil to drip out while you repeat htis step for the other fork. I just poured the oil out until it was barely dripping and deemed it good enough.

Step 10 - Springs and washers
Put your spring (old or new, depending on what you're doing) into the now empty fork leg. Place a washer on top of the spring.

Step 11a - Fork oil change only
Measure out between 375mL and 382mL of new fork oil in your measuring cup and pour it into the fork leg. Put the spacer back in and compress the spring, washer, and spacer with the fork cap. It helps to have a friend compress the spring while you screw the cap on via turning the fork leg. BE CAREFUL! If you feel the cap starting to cross thread stop IMMEDIATELY and unscrew the cap and try again.
Repeat steps 9-11a with the other fork leg. Be sure to use the same amount of fork oil in each leg. Reinstall through the reverse steps 1 through 8. There! You're done! Hooray!
Dispose of your fork oil in a proper container. Old motor oil bottles work great.

Step 11b - Performance spring replacement & fork oil change
Using the tape measure, measure the distance from the top of the spring washer to the top of the fork leg. Record this distance (D1). Measure the fork cap height - the distance from the bottom of the fork cap where the cap touches the washer to the bottom of the o-ring where the top of the fork leg touches first (~14mm to 15mm). Record this distance (D2). D1 - D2 is the length of spacer needed for ZERO preload. Standard preload is about 20mm.

Step 12 - Cutting spacers
Using (D1 - D2) + preload distance (I used 20mm), mark your spacer material accordingly. RaceTech springs come with 6061 aluminum spacer material. Use the hacksaw to cut your spacer and the file to clean up the edge so that it is smooth. +/- 1mm is insignificant. It helps to have a friend hold the spacer material while you cut it. It's possible to cut the stock spacers (which are about 200mm long), but I prefer not to. Personal preference.

Step 13 - Fork oil & reassembly
Measure out 375mL to 382mL of fork oil and pour it over the spring and washer in the fork leg. Place the spacer in the fork leg and place a washer on the top. Using the fork cap, compress the spring and thread the cap. Again, it helps to have a friend compress the spring while you rotate the fork leg to thread the cap on. BE CAREFUL! If you feel the cap starting to cross thread, stop IMMEDIATELY and unscrew the cap and try again.
Repeat steps 9 through 13 for the other fork leg. Be sure to use the same amount of fork oil in each leg.
Dispose of your fork oil in a proper container. Old motor oil bottles work great.

Step 14 - Reinstallation and sag
Reinstall your forks following the reverse of steps 1 through 8.
With the front wheel off the ground, measure the distance from the top of the lower fork leg (the big part of the fork) to the bottom of the bottom triple clamp. This is L1.

Push down on the forks and let them rise slowly. DON'T BOUNCE. Measure the distance from the same locations of where they stop. This is L2.

Pull up on the forks and let them sink slowly. DON'T BOUNCE. Measure the distance from the same locatins of where they stop. This is L3.

For L2 and L3 you need to balance yourself on a wall or have another friend balance the bike while you sit on it in your normal riding position. Feet should be off the ground.

Sag is:

S = L1 - (L2 + L3)/2

For normal street riding, sag should be set around 30-40mm.
For agressive street riding, sag should be set around 20-30mm
For racing, sag should be set between 15 and 25mm.

If your sag is not set in the area you want, pull the fork caps off and adjust preload accordingly. No need to take the forks out.

For reference, I weigh 130lbs. I used RaceTech .8kg/mm fork springs, Silkolene 5W fork oil, and had 20mm of preload. My sag was also recorded at ~20mm.



DISCLAIMER: I am not a professional. This is meant to be instructional only can I can take no blame if anything is to happen to your bike. You perform these actions at your own risk and may take no action against me should something go wrong. If you doubt your ability to perform these actions, take your bike to a professional mechanic in order to have the work done and backed up with a guarantee. I make no guarantee that everything is correct, rather only to the best of my knowledge.

Be sure to read over this fully before attempting to work on your motorcycle and make sure that you understand what needs to be done before you begin. If you have questions feel free to ask.


Torque Specs:
Front Axle nut:          36-52 Nm   --   26-38 ft lb
Bar clamp bolts:          8-12 Nm   --    6- 9 ft lb   --   71-106 in lb
Upper triple pinch bolt: 18-28 Nm   --   13-20 ft lb
Lower triple pinch bolt: 25-40 Nm   --   18-29 ft lb
Front caliper bolts:     30-48 Nm   --   22-35 ft lb

For the bolts holding the front fender, just make sure they are good and snug.


Links and Sources for Springs:
Links
RaceTech spring rate calculator: First go here. Select Suzuki, then GS500, then your year model. If you have an '04+, the '01-'03 one works as well. Click Continue. Click the large red text that says Custom Fork Spring Calculation and Available Rates.
Peter Verdone suspension information here
Springs
Straight Rate
Race Tech - $109.99 + shipping
Sonic Springs - $79.95 + shipping
Progressive Rate
Progressive Springs Product number 11-1128, or search for "111128" on eBay. $49.95 + shipping

EDIT: Cleaned up a few links and organized a few things better. Added torque specs and sources for springs.
'05 DR-Z400SM (For Sale)
'04 GS500E (Sold)

Holy crap it's the Wiki!
http://wiki.gstwins.com/

MarkusN

I have found it easiest to loosen (not open) the fork caps before loosening the tripple clamps. The forks are tightly clamped in the triples to hold them; something that's not easily done in a vise with the fork legs out.

Alphamazing

Quote from: MarkusN on April 17, 2006, 03:10:48 PM
I have found it easiest to loosen (not open) the fork caps before loosening the tripple clamps. The forks are tightly clamped in the triples to hold them; something that's not easily done in a vise with the fork legs out.

See Step 1.
'05 DR-Z400SM (For Sale)
'04 GS500E (Sold)

Holy crap it's the Wiki!
http://wiki.gstwins.com/

Onlypastrana199

I just want to point out that my stock springs didn't sag when I was on the bike, and may not for other little people like me. They did bottom out though on a couple of occassions, so I stiffened mine up also, but considering I didnt want it too stiff I didnt replace the stock springs.
'93 cf two bros can, alsa cobalt blue custom paint, fenderectomy, repositioned directionals, 15t sprocket, ignition advancer, SM2's, national cycle f-16 dark sport, cbr rearsets - fully rebuilt after a crash

RVertigo

What about torque settings?  They in the manual somewhere?   :dunno_white:

Alphamazing

Quote from: RVertigo on April 17, 2006, 03:30:12 PM
What about torque settings?  They in the manual somewhere?   :dunno_white:

Yeah. The manual is at home. I'll add the torque specs whenever I go get it.
'05 DR-Z400SM (For Sale)
'04 GS500E (Sold)

Holy crap it's the Wiki!
http://wiki.gstwins.com/

Destro

I just did mine today!  :laugh: Only had to make 2 trips to the parts store. Thought we needed an update to the FAQ.  Nice work!  :thumb:
-Shayne
'92 GS500
'00 YZF600R

Alphamazing

Quote from: Destro on April 17, 2006, 06:48:10 PM
I just did mine today!  :laugh: Only had to make 2 trips to the parts store. Thought we needed an update to the FAQ.  Nice work!  :thumb:

Thanks!

I added some links for spring rate calculation and some extra suspension information links at the bottom of the first post.
'05 DR-Z400SM (For Sale)
'04 GS500E (Sold)

Holy crap it's the Wiki!
http://wiki.gstwins.com/

mike_mike

2005 GS500F (blue)
Location: Toronto, Ontario, Soviet Canuckistan

Alphamazing

Quote from: mike_mike on April 17, 2006, 07:47:42 PM
no pics?  :)

I was too busy figuring out wtf to do to take pictures. Next time I go home (weekend, maybe) I'll snap some pictures and get the torque specs when I do, though.
'05 DR-Z400SM (For Sale)
'04 GS500E (Sold)

Holy crap it's the Wiki!
http://wiki.gstwins.com/


Alphamazing

Alright. I cleaned up a few things, organized a few things a bit better.

The main things I added were torque specs and sources for springs.
'05 DR-Z400SM (For Sale)
'04 GS500E (Sold)

Holy crap it's the Wiki!
http://wiki.gstwins.com/

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