Author Topic: another fork question  (Read 9469 times)

Offline Farre

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another fork question
« on: May 08, 2006, 08:28:25 AM »
I have another question about forks that i haven't seen discussed before..

I bought a while back GSXR400 forks (GK73) they're almost identical to the B4 except for adjustable dampening (right?) and the installation for double discs.
Well, i can't get any decent price for only the discs and calipers so now my mind has been wandering of to use the inner tubes of the gsxr in the outer tubes of the b4. Perhaps it is possible, but maybe they are 'matched' inside the factory or something..

Another tidbit, the b4 forks have a small bend somewhere, i suspect it's only in the inner tubes, the outer ones seem much stronger so i doubt they have been affected, maybe this can have an impact if the earlier question is answered 'positively'.

I know my idea sounds cheap, but to find a complete front end of naything bigger is an almost impossible task in Belgium! Everybody wants these it seems

Well,... thanks in advance for the advice (if any :wink: )
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock

Offline BrianM

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another fork question
« Reply #1 on: May 08, 2006, 11:36:23 AM »
I've done a number of swaps (F3, rebound adjustable cartridges and tubes into SV's, VFRs, 1 set of F2 lowers, etc).  Shouldn't be an issue.

And the lower leg CAN be bent, but it's pretty rare and usually fairly obvious.  You can easily test that after disassembling, just check the tubes with a dial-guage for trueness, then insert into the lowers and run it up and down while feeling for tight spots.  The OLD tubes can also show, just look at the lower bushing and see if there's 1 spot that's worn off more than the rest.  Though, this isn't the 'end all, be all' test.  You can also check them with a dial guage.

So, in short, you should be good to go.
Cheers,

     BrianM ~ 1991 Bandit 400

Offline gsxr400 racer

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another fork question
« Reply #2 on: May 08, 2006, 10:32:39 PM »
yes put the 400 gixxer inners in the b4 outters good to go.
1988 gsxr 400 sp (sprint bike)
*  SELLER OF THE 442CC BIG BORE PISTON KIT FOR THE BANDIT 400,GSXR400, GK73 and 76.* And carb kits(orings)too. Email me from here.
has been a wera expert #610 lol

Offline magicGoose

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another fork question
« Reply #3 on: May 09, 2006, 08:55:17 AM »
So, you're giving up on the dual disc conversion, and you have a good set of GSXR400 forks and a bent set of bandit forks which you want to make into one good set of Bandit forks?
If that is the case, I would look into getting the inner tubes straightened. They usually bend right below the lower triple tree clamp. This will cost a few euros but it may be a lot simpler than trying to swap parts. I have had '91 400 Bandit, '86 GSXR1100, and early '90s 750 Katana forks apart, and although they are all 41mm Suzuki forks, the parts are incompatible. I don't know about the GSXR400 forks though.
If you do decide to open them up, please keep us informed on what you find.
Good Luck,
Steve
1991 B4

Offline Farre

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another fork question
« Reply #4 on: May 10, 2006, 04:51:32 PM »
well, i MUST use another fork.. the B4fork has serious pitting issues, seals were perfect, then riding with a pillion over a big bump and all of a sudden they were leaking! Checked with the fingernail technique and BINGO.. 3 deep pits found in both forks..

I don't think i'll do it right away, i prefer to wait till summer vacation and fix the rest of the bike first (R/R, Battery, Rear Wheel bearings, and finding more! :sad: )
And i need more info about these pogo-like thingies.. This is a 'grey area' for me, never seen one opened up and i feel uncomfortable about installing those seals and the special tool required. Herr Todd explained me, and i thank him for that but i need someone to really show it to me... maybe i can find a 'friend of a friend' that's willing to help me out.
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock

Offline BrianM

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another fork question
« Reply #5 on: May 10, 2006, 06:41:50 PM »
I'm about to refurbish my forks (rusting, pitting, needs seals)...  I was already planning on taking pictures and doing a write-up for the Ninja250 FAQ, but I'll post it over here aswell.  I'm waiting on the fork seals at this point, but it should only be another week or two before I tackle the forks.
Cheers,

     BrianM ~ 1991 Bandit 400

Offline Farre

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another fork question
« Reply #6 on: May 11, 2006, 03:48:20 PM »
Thanks, it'll be very much appreciated ...
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock

Offline GK75A

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another fork question
« Reply #7 on: May 11, 2006, 04:39:14 PM »
try allbike engineering, here in the uk. forks listed at £80 each

Offline BrianM

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As promised...
« Reply #8 on: May 24, 2006, 12:53:04 AM »
First things first, you need to decide if time or money is more important... if time is more important, then just pull the forks and deliver them to a dealer for a fork seal change, expect to spend $100~120. If money is more important and you have some Basic hand tools, a tiny bit of common sense and about $20 you can change them youself.

First things first, you'll need some fork seals ~ K&L Supply is where the Pros buy their from, about $12/set~, a quart of 15wt Damper Rod Fork Oil and some 400 grit sand paper and a legnth of PVC Schedule 40 that fits over the fork tube and inside the fork leg. Rubber gloves, contact cleaner and rags/paper towels sure do come in handy too.

You're going to need to support the front end off the ground durring this task (unless you have enough money to just give it to someone and let them do the work), I have a purpose built front end stand. Most others use floor jacks with a length of 2x4 between the jack and the headers (this only works if you have the stock center stand), some people run tie-downs from the rafters to points on the frame and lift it that way. Figgure out your method and have it ready. Next, break over (loosen a 1/4~1/2 turn) each of the 7 bolts/nuts you can get to, this is important to do Before lifting the bike as you'll be unable to supply the proper torque with the bike in the air.



Now, lift the bike (the wheel only needs to be about 1" off the ground)



and remove the brake caliper (make sure not to let it hang from the hose ~ this can cause leaks),



remove the axle/wheel, loosen the fender bolts (it won't remove easily), then one fork at a time loosen the lower and upper triple clamps. The forks may, or may not, just slip right out. If the triple clamp bolts are loose, then you can just twist the forks while pulling down and they should work themselves out.


With the forks out, it's time for disassembly. I'm going to list a few different methods for a couple of steps so you know the different options. First is breaking over the allen bolts that hold the damper rods in place. If you Don't have a vise, you'll need to do this Before removing the forks.  Slide the axle through one leg and partially through the 2nd leg, leaving enough room for your allen key to get up to the bolt, and loosen.  



If you have a vise, just put the axle clamp area in the vise (ONLY that area, it's Very easy to do damage otherwise) with the bottom of the fork facing up.



You'll see an 8mm allen screw dead center ~ just break this over so it's loose (I have sockets, if you only have keys try using an extended lever to get the needed torque. If it spins and doesn't loosen, you'll need to either use an impact or compress the fork and try again). With that done, it's time to remove the cap and dump the oil... Anyway, with the fork upright remove the washers, spacer and finally the spring while spinning it to keep the oil dripping to a minimum. Then dump the remainder of your oil into a drain pan. While that one drips, get the other fork to the same stage.



With the forks at this stage, you should be able to easily remove the allen screw on the bottom and have the damper rod drop out.



Now you need to remove the dust cap (pry it up with a small/skinny flat blade screwdriver), and the retaining circlip (screwdriver again). All that's left is to slidehammer to inner and outter tubes apart. This may take a bit of muscle, but they Will come apart. The parts are, from left to right, the outer bushing (cliped to the fork leg), inner bushing, washer and oil seal:



The bushines are copper with a teflon coating.  If you see copper 'specks' through the grey teflon coating, it's time to replace them.  Ditto if you see other metal bits imbeded on the bushings.

With the tubes apart (BTW, do both at the same time - it's a minimal ammount of extra work and you can ensure that the other fork won't start leaking 5 miles later), you can wipe them down and give them a good sanding. 99% of the time when fork seals go it's because of rock dings and dried bug guts that slide past the seals. The raised edges cut the seal to shreds and you get a leak. Ideally, you want to give the forks a good cross-hatch and smooth everything out.



This is the type of ding to be on the lookout for...  above is rust.  It's above the range of the oil seal, but unsightly and I sand it off.


Now clean Everything as best you can.

Time to start assembly. Install the tube into the leg (with the lower bushing already on the tube), then the upper bushing and the metal washer. Now seat these with the PVC pipe you aquired (if it's long enough to sit over the top of the fork, you can just tap it down with a mallet). Next is the seal itself, but you neet to take a couple of precautions ~ first put some suran-wrap or a plastic bag over the end of the fork - this will help the seal slide on without tearing itself.  For those who've not seen oil seals, here's one:  Top (facing up) first, and bottom second:





Also, I like to lube the inside of the seal - at home I use my trusty BelRay Waterproof grease... when doing it for a living I used the SuperSlick RaceTech grease. At home I also run the old seal ontop of the new one so I don't chew up the new one seating it with the PVC pipe.


I ripped a 'kerf' down the legnth of my PVC because it was slightly small...  

Install the snap ring and dust seal. The snap-ring goes into this groove (so make sure you've seated the oil seal far enough):



Now, drop the damper rod back into the fork, then put the spring ontop of it. With the fork laying on a work table, spring pressed firmly against the wall you should have More than enough friction to reinstall the allen bolt. Do NOT use any loctite here as it will make the forks nearly impossible to disassemble in the future. Once the damper rods are installed, fill with oil and set the level (remember to work the fork tube up and down to bleed out the air). There are plenty of ways to set the level, I just use a 6" metal machinist ruler:



Then reinstall the spring, washer, spacer and cap. Now you're back to installing the fresh forks on your bike ~ this is simply the reverse of removing and you Should be home free.

Hopefully this helps some.  Other tips, keep bug guts from your forks And you can sand down rock dings with the forks on the bike to help prevent/prolong seal life.  When the forks are apart, completely colapse them and mark how fark the forks go (I just use a center punch and put a ding in the tubes, it never goes over the fork seal ~ BUT, it Needs to be sanded down before installing the fork seal ~ this gives you an indication of how much space needs to be sanded and for those who are pushing the bike hard, you can place a zip-tie around the fork leg and see how much total travel you're using.  You Want to be as clean as possible when doing this, obviously.  If you have a hard time getting the bottom socket-head cap (allen) out, take a $5 or $10 and the forks to a motorcycle shop and ask a mechanic to do it for you...  then tip them.  It takes about 20 seconds to do both forks, isn't a bother and will establish good will with them (should you need help in the future...  goes along the lines of when you go to a bar, Always pay cash for the first round, and tip Heavily ~ guaranteed good service for the rest of the night).  

Anyway, this is maybe a slightly more advanced task, but well within the realm of a DIYer.

Brian

^^^^^^^^^^^^^^^^^  the above is a cut and paste from my 250 forums, I edited a few things that were specific to that site but may have missed some.  It's Scary when the 'stuff' that comes out of the forks is clumpy and grey/silver...  not to mention I don't think I got a total of 20ml from BOTH forks, combined.  All the oil ran down the legs, and soaked into the pads (the rotor was Completely covered, took 3 rags to get it clean!!)  Damn people who trust their lives to bikes they don't maintain/have maintained...  it's a wonder they survive.

Oh, and this is another fork page I wrote up a few years back....

http://forks.darladog.com/
Cheers,

     BrianM ~ 1991 Bandit 400

Offline Farre

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another fork question
« Reply #9 on: May 24, 2006, 10:16:25 AM »
this is great! i especially like that you made pics at critical moments.
So that special tool mentioned in the Suzuki manual is to keep the damper rod firm from the inside, which you negated by using a vise or the front wheel axle, correct?
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock

Offline BrianM

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another fork question
« Reply #10 on: May 24, 2006, 10:55:07 AM »
The "special tool" keeps the damper rod from spinning (mine was a Bitch, but there was loctite on it, so it was caused by some hack mechanic).  Generally speaking (meaning, of the ~ 2500 forks I rebuilt durring one of my jobs, I only had issues with about 10~15), the friction afforded from compressing the fork or extending it will be enough for anyone to remove the screw with basic hand tools.  The vise/front axle just keep the lower fork leg from spinning..

One picture I didn't show for this is turning the fork on its cap and pushing down while turning the screw.  I was a bit peeved by the time I got to that stage because my forks were being a pain.  You need to take obvious precautions to not ding up anything (I was pushing mine into an anti-fatigue mat, soft and cushy).  

Anyway, glad this helped you.
Cheers,

     BrianM ~ 1991 Bandit 400

Offline Farre

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another fork question
« Reply #11 on: May 24, 2006, 11:05:35 AM »
Perfect! Thank You very much!! Finally it's all clear to me, i have seen the light!  :lol:
I expect to start with the replacements beginning of July
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock

Offline Farre

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another fork question
« Reply #12 on: June 28, 2006, 06:17:42 AM »
i think i got scammed at the stealership, i specifically asked for B4 fork seals and i paid and went home (i believed they were competent!). Now i notice the seals are for B6's :sad:
IIRC, B4's are 41mm and B6's are 43mm, thus they cannot be interechanged, correct?
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock

Offline PitterB4

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another fork question
« Reply #13 on: June 28, 2006, 08:40:13 AM »
Nope - The 4 and 6 are both 41mm.  It's the 12 that has the beefier 43s.

AFAIK you should be OK.
Rob
Bikeless!
'93 Bandit 400 - SOLD
'98 Honda F3 Track Bike - SOLD
'98 Kawi ZX-6R Street Bike - SOLD
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Offline Farre

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another fork question
« Reply #14 on: June 28, 2006, 08:57:40 AM »
oh thank God!  :thanks:
Alex
'91 B4 almost bone stock:
GK73 Inner forks& Springs
B6 Rear Shock