Ralph Fer­rand sorts out the forks.

Classic Motorcycle Mechanics - - CONTENTS -

Time to strip down a pair of up­side-down forks from a GSX-R750 WP… I don’t know why, but I have never liked in­verted forks and for me they have al­ways rep­re­sented moder­nity and the end of bikes as I knew and loved them. For this job, how­ever, I had to shelve my prim­i­tive prej­u­dice and learn how to re­build th­ese more modern front forks. In re­al­ity they were noth­ing like as com­pli­cated or dif­fi­cult as I had been led to be­lieve and (aes­thet­ics aside) I would not be con­cerned about re­build­ing an­other set. Th­ese forks, along with the rest of the bike had not been stored in ideal con­di­tions and the hard chrome plat­ing on the stan­chions was per­fo­rated and rust was de­vel­op­ing in the steel leg un­der­neath. If time and money was no ob­ject, a good solution would be to have the legs stripped of chromium, re-plated and ground, where you can ex­pect a job quite con­sid­er­ably bet­ter than the orig­i­nal. In this sit­u­a­tion the bike isn’t go­ing to rack up hun­dreds of thou­sands of miles in ad­verse con­di­tions and costs have al­ready been get­ting quite bank ac­count bust­ing for my long-suf­fer­ing cus­tomer, so I got a pair of Ital­ian made Tarozzi pat­tern fork tubes, which to the trade are quite a bit cheaper than re-chroming the orig­i­nals and the qual­ity is at least as good as the orig­i­nal stock com­po­nents. Be­fore at­tempt­ing any sus­pen­sion work one must en­sure a de­cent bench vice with a good qual­ity set of soft jaws. Sus­pen­sion com­po­nents need to be clamped se­curely, but gen­tly as the lion’s share of the com­po­nents are made from light­weight alu­minium al­loy which is eas­ily dam­aged. Once the leg was safely se­cured in my bench vice I picked the spring ad­juster stop­per ring out of its groove us­ing a pick tool and then care­fully stashed it. With jobs like this I al­ways have lots of Tup­per­ware type con­tain­ers to keep such eas­ily lost parts to­gether. With this out of the way, I was now able to un­screw the spring ad­juster bolt and then re­move the ad­juster it­self. Be­cause the fork cap is so eas­ily dam­aged and is right in the line of sight of the rider I al­ways use spe­cial non-mark­ing fork cap span­ners made of en­gi­neer­ing grade plas­tic. They’re not espe­cially ex­pen­sive and will pre­vent dam­age to this vul­ner­a­ble and costly to re­place com­po­nent. Once the fork cap was re­moved it was time to break out the spe­cial fork tools. The first tool out is the fork spacer hold­ing tool which from Suzuki (Pt No 09940-94930) is well over £100, but our pat­tern item man­u­fac­tured by Bri­tish com­pany Laser Tools is just over a score. With the bot­tom of the leg se­cured in the vice, I was able to com­press the fork spring pulling down on the tool and SWMBO kindly slipped in the fork damper hold­ing plate un­der the lock nut se­cur­ing the fork cap to the top of the damper rod. She really does like to be in­volved, or so I keep telling her.

With the plas­tic fork cap span­ner hold­ing the fork cap I used a 14mm span­ner to re­lease the lock nut and was then able to un­screw it from the damper rod. The spring was com­pressed again to re­move the damper rod hold­ing plate so that the spring, its seats, spac­ers etc. could be ex­tracted. I then de­tached the re­bound damp­ing ad­juster from the damper rod by re­leas­ing its lock nut. The next part I never en­joy; re­mov­ing the fetid, mal­odor­ous sus­pen­sion fluid in­side. The fork was in­verted over a suit­able con­tainer and pumped re­peat­edly to re­move all the vile swamp juice from the damp­ing sys­tem and was them left in­verted to drain for a while. The next stage was to re­lease the damper rod from the bot­tom of the leg where it is se­cured with a fine thread M10 cap screw. Ex­pe­ri­ence has taught me that the eas­i­est way to re­move damper rod bolts is with a mega pow­er­ful air im­pact wrench, which sneaks up on them and whips them out be­fore they know what’s hap­pen­ing. Suzuki’s fac­tory ‘how to’ publi­ca­tion does not men­tion this cav­a­lier method­ol­ogy, rather sug­gest­ing that if it doesn’t come apart eas­ily then you might want to try re­fit­ting the spring and al­lied com­po­nents to help hold it still. Damper bolts al­most never give in eas­ily as they are usu­ally fit­ted with thread lock and seal. The in­stant high torque of a high-end windy gun gets my vote ev­ery time;

it might sound gra­tu­itously vi­o­lent, but it seems to cause the min­i­mum of pain and grief and I have never had it go wrong. It should go with­out say­ing that much care must be ex­acted when us­ing any form of in­dus­trial power tool. More of­ten than not when, us­ing an Allen key, the bolt turns a tiny bit and then spins, mean­ing that you really have to some­how lock the damper rod which is fre­quently prob­lem­atic. Un­der the head of this bolt will be a soft metal washer of ei­ther an­nealed cop­per or alu­minium. Th­ese are one use only so en­sure that they are re­placed. The re­ward for par­si­mony at this stage will be a leak­ing fork leg and I tend to coat th­ese wash­ers in a layer of RTV sil­i­cone af­ter a thor­ough de­greas­ing as there can be few more an­noy­ing things than the fork bolt leak­ing. With the damper rod out it was time to ex­tri­cate the vil­lain of the piece, the in­ner fork tube. First the dust cover, seal clip and main hy­draulic seal have to be re­moved as well as the bear­ing at the bot­tom of the outer tube. Rather an­noy­ingly the bear­ing was as tight as a York­shire­man de­prived of his nat­u­ral sense of gen­eros­ity. The first stage was to spray plenty of ACF-50 into it, which is not only a very good pro­tec­tant, but is also a very pro­fi­cient pen­e­trat­ing fluid and has some chem­i­cal in it that, to a de­gree, re­verses alu­minium al­loy cor­ro­sion. Af­ter a good soak in ACF-50 I warmed up the alu­minium sec­tion with a heat gun be­cause alu­minium ex­pands faster than steel, so this gives me a bit more movement. As the in­ner leg is pulled from the outer leg the lower bear­ing, at­tached to the in­ner leg, pushes against the up­per bear­ing, which in turn pushes against the thick steel washer which acts on the hy­draulic seal. The fac­tory man­ual sug­gests that both the bear­ings and the seals, dust and hy­draulic, should be re­placed at this stage. The bear­ings are still avail­able from

Suzuki; the in­ner has a part num­ber 51121-48B31-000 and the outer 51168-08B00-000. Our chums at We­moto sell pat­tern bear­ings at some­what less than half the OEM price and can also sup­ply all the seals and the stop­per rings. I re­moved the com­pres­sion damp­ing force ad­juster and noted that Mr Suzuki for­bids tak­ing this part to pieces; given it was fine this was okay by me. The in­ner fork tube is screwed into the bracket that takes the wheel spin­dle and an­chors the brake caliper, but be­fore un­do­ing it, there is a tiny and easy to miss lock­ing grub screw which must be loos­ened first. I se­curely clamped the bot­tom bracket in the vice us­ing soft jaws. There are some holes just be­low the groove for the in­ner bear­ing and I pushed through a suit­able di­am­e­ter piece of mild steel round bar to act as a tommy bar. The thread was locked with a chem­i­cal lock and seal as well as the grub screw so I had to heat up the bracket to break this bond at which point I was able to care­fully un­screw the leg. I sent the brack­ets off to Mikey’s Pol­ish­ing Shop for a qual­ity mir­ror pol­ish. This bracket was show­ing its age and as the bike was a cus­tom ma­chine I thought a mir­ror fin­ish here would look great. The an­odized fin­ish on the outer legs was in ac­cept­able con­di­tion and a mir­ror fin­ish on them would prob­a­bly have been too much, par­tic­u­larly as the yokes had a high grade pol­ish. One has to be care­ful not to over-bling a cus­tom ma­chine or it starts to look se­ri­ously tacky. I care­fully clamped the now shiny bracket into the bench vice and ap­plied some thread lock and seal to the threads of the new stan­chion be­fore screw­ing it into its new home. I used the tommy bar to tighten it up and then re­placed the lock­ing grub screw.

Re­mov­ing the spring ad­juster stop­per ring.

The fork spring com­pres­sor tool is pulled down so that the damper rod hold­ing plate can be fit­ted.

Loos­en­ing the fork cap bolt with a spe­cial non-mark­ing span­ner.

Fork spring com­pres­sor tool fit­ted.

Fork cap un­done.

Un­screw­ing the spring ad­juster bolt.

Re­mov­ing the spring ad­juster.

Lift­ing the ad­juster clear.

The damper rod hold­ing plate fit­ted – you’ll need a SWMBO or equiv­a­lent to fit this while you com­press the spring!

Plas­tic span­ner and 14mm open ended span­ner re­leased the lock nut and al­lowed the fork cap to be re­moved.

Warm­ing up the fork with a heat gun in an ef­fort to per­suade the old fork seal and bear­ings to move home.

Us­ing ACF-50 as a pen­e­trat­ing oil.

Damper rod out.

Us­ing a pick tool to ex­tract the fork seal se­cur­ing clip.

Re­mov­ing the spacer, spring, spring seats etc.

A big man-size air gun makes the damper bolts come out!

Slid­ing out the damper rod.

Lower bear­ing Outer fork tube Up­per bear­ing Seal spacer washer Fi­nally the fork tube with bear­ings and seals came out. In­ner fork tube Hy­draulic fork seal

Un­do­ing the grub screw that stops the fork lower un­screw­ing from the in­ner tube.

A piece of milt steel round bar was used as a tommy bar to tighten the in­ner leg into the bracket.

A drop or two of thread lock and seal on the threads of the new in­ner legs prior to rein­ser­tion.

The brand-new stan­chion screwed and se­cured in a lovely shiny fork bot­tom bracket.

The lower fork leg bracket clamped in the vice ready for re-assem­bly.

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