Whether it’s from decades of neglect or a dutiful service interval of soaking up potholes, the day will come when your suspension pukes its guts out. Rubber seals have a finite lifespan, fluids break down over time and the chrome on your fork tubes and shock shafts will eventually fail and corrode. The telltale sight of a leaking seal brings with it the decision to repair/replace stock components or undertake a major suspension upgrade.
While there’s no shortage of mono-shock conversions and front-end swaps around here, the theme of our everyman Honda CB550F tracker project calls for an accessible and affordable approach—something anyone could accomplish in a weekend to get an old bike on the road again.
Rebuilding Telescopic Motorcycle Forks If you want to play around with old bikes, you’ll either become proficient at rebuilding forks or get used to paying someone else to do it. A neglected classic will almost certainly come with an oil leak on the left side, and you’ll have to tear the fork down completely to fix it. The good news is that it’s not that complicated, because what your classic motorcycle lacks in ride quality, it usually makes up for in simplicity.
Every design is a little different, even among telescopic forks, but our Honda CB550F is certainly the easiest rebuild I’ve done. Really, you’ve got six major pieces per side, and driving the new seal in doesn’t require any specialty items.
Disassembly is pretty straightforward, but there are a couple of pieces of advice that go a long way with this style fork. There’s a small Allen-head cap screw in the fork lower that’s concealed where the axle is housed, and it pays to knock this loose before removing the fork tubes from the triple clamps. A small impact driver works well, and you only need to loosen it slightly at this stage. Also, if your bike is as rough as ours, a dead-blow hammer or a wooden dowl is a must to free the fork tubes from the triple clamps.
With the forks on the bench, you’ll be able to break each tube down in just a couple of minutes. The large cap at the top loosens easily with an impact, and then you’ll want to remove the hex-head drain bolt on the fork lower. Stroke the fork slowly several times with a catch pan to extract the nasty old oil. After that, completely remove the Allen-head bolt at the bottom, and you’ll be able to remove the spring and dampener.
Next, it’s time to remove the old fork seal, and our CB550’s original seals put up one hell of a fight. After removing the snap ring, it took a large pry bar to free the seals from the fork lower. With the old seal out, you’ll be able to knock out the oil lock from the fork lower.
Before reassembly, you’ll want to clean and inspect all your parts, and our neglected CB550 was a pretty tough case. Our fork tubes had serious pitting and rust around the triple clamps, and the lowers had heavy corrosion and trashed clear coat. If you have the means, some of these parts merit replacing completely, but in the spirit of making something from nothing, we did our best to clean up what we had.
Tidying up the fork lowers wasn’t bad. I plugged the holes with rags and popped them in the sandblaster to clean off all the old clear coat and corrosion, and then finished them off with WD-40 and red Scotch-Brite for a more OE finish. If you don’t have access to a blaster, a brass wire wheel should do the trick, and clear-coating these parts afterward is probably worthwhile.
Corrosion on your fork tubes is more concerning, as these pieces are plated and need to have a perfect finish against the fork seal. If your tubes are pitted in any place the seal interfaces, they should be completely refinished or replaced. Our situation was only slightly better, as the corrosion was limited to the triple clamp area, far from the fork seal, but the pitting was through the chrome.
Call it doing the wrong thing the right way, but I chucked both of our tubes in the lathe and lightly sanded and polished the affected area. This won’t harm the fork seal, since it’s outside the seal’s travel, but you’ll want to coat that part of the tube with some sort of protective finish to prevent corrosion later. If the difference in the finish catches your eye, a dirt-bike-style dust boot (or gaiter if you will) completely conceals the area, and we may swap our dust covers later.
With everything prepped and cleaned, drop in the oil locks and the new seals can be installed. As always, coat the seal with a little oil and you can use the old seal to drive the new one in before installing the snap ring. From there it’s easy. Install the dampener and spring into the fork tube and replace the drain bolt and Allen head screw in the bottom.
For oil, Honda recommends 10W30 motor oil, or even ATF for our CB550 fork, but we had something heavier in mind. The folks at Common Motor Collective recommend 15W40 for heavier riders, and we’re hoping that gives us improved dampening when our CB (inevitably) sees some light hooning. 170 cc of oil fills each fork, and then we’re ready to replace the top cap and refit our fork tubes.
Replacing Motorcycle Rear Shocks After servicing the front fork, replacing rear shocks is a much simpler nut-and-bolt affair. Rebuildable shocks are worth having serviced, but otherwise, you’ll be shopping for new ones, and the easiest approach is an application-specific shock. If you don’t mind shopping around or want to change the stance of your bike, you’ll need to figure out your desired ride height, spring rate, travel, etc. to pick a universal shock. Keep in mind that your bike’s mounting style (eye-to-eye, eye-to-clevis, etc.) and bushing size will narrow your options.
In the end, we settled on a budget-friendly, remote reservoir shock from Tec Bike Parts. It’s nothing fancy, offering only preload and height adjustment, but we had to give it a shot for the price point. If your budget allows, a rebuildable shock with compression and rebound adjustability is the best money can buy for your old twin shocker.
Unsolicited Final Thoughts What our CB550 tracker project lacks in glamor, it certainly makes up for in cheap thrills. Our investment in the bike and the parts we’ve sourced is so minimal, but it gets incrementally better with every job completed. There’s no doubt we could have coughed up for pricer shocks, or done something more exciting with the forks, but in the spirit of making something from nothing, I think we’re getting somewhere.
I have a bunch of loose ends to tie up next, including some trimming to tighten up our seat fitment, tabs to remove and brake parts to replace. I have a few ideas to improve the old aftermarket exhaust our bike has as well, but we’re still up in the air on that. We’re also still feeling out the front fender situation, and I need to get around to cutting up our stock one. The point is, there’s still work to do before we get to the exciting stuff, and we have a few surprises in store as well. Stay tuned.
Bike EXIF thanks Motogadget, Tuffside, Bridgestone, Lowbrow Customs and Biltwell Inc. for supporting our Honda CB550F tracker build.