Ralph Ferrand sorts out the forks.
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.