Honda CB550 fork rebuild with RaceTech springs & emulators
Originally when I thought through my CB550 cafe racer build I was going to put a Suzuki GSX-R front end on as it seems to be the “done thing”. To do that I’d have needed a Cognito Moto triple tree & wheel hub plus GSX-R forks, calipers, brake disks and lines - a very expensive modification at around £1,600 for parts, shipping, import tax etc.
Over the months I bought some GSX-R parts - brake disks, spindle, brake pads & master cylinder in prep for the swap out but the more I got into the build, the more I went off the idea of mixing modern Suzuki parts with vintage Honda. Even though I'm making a cafe racer by chopping parts off and changing things, I feel that the main lines - frame, engine, tank, forks & brakes should stay true to the original bike.
I did some research and was initially going to put progressive Hagon springs in to match the rear shocks but after reading on forums I decided to go with RaceTech springs and cartridge emulators. Yes, this is stepping away from the original Honda engineering but I'm all for modern tech and a better ride quality. Visually, nobody will know any different.
RaceTech springs and Gold Valve Cartridge Emulators
Emulators basically turn an old dampener rod fork into a modern cartridge fork. RaceTech were the first to come up with this idea. As usual, all the good “toys“ are made in America but there is a U.K. re-seller called PQD. Technical details for the CB550 can be found here.
Matt Wiley from RaceTech is super helpful and I had a few emails with him before making a decision. They have an online calculator to help you choose the correct spring rate. Stock is .68KG, the calculator suggested .70KG, Matt suggested .75KG and the guys at PDG suggested .70KG. I ended up going with .70KG knowing that the bike would be a lot lighter than stock. With that choice, Matt suggested adding more pre-load than documented - I’ll go into more detail later.
This is my first time both rebuilding forks and using fork emulators so there was a big learning curve. I’m used to (and prefer!) things to be black & white. It turns out that shocks are a bit more grey in terms of the various spring rates, damper holes, pre-load on the emulators, pre-load on the springs, fork oil viscosity & level.
RaceTech have a system called DVS (Digital Valving Search) that you fill in your details (bike, body weight, riding style, preferred stiffness etc) and it gives you a list of all technical specs for your install. But, as Matt says, this is a starting point and through email chats with him I’ve gone off-piste with a few settings.
The RaceTech parts I got from PDQ where:
Gold Valve Cartridge Emulator Kit (FEGV S3001)
Fork Emulator Adapters (FPEV AD3003 P)
.70KG rated springs (FRSP S2341070)
15W fork oil - not RaceTech but Putoline HPX R.
All of this came in at £320.
Stripping the front forks
As with most things on the bike, this was my first time so I looked on YouTube and found a couple of great clips for stripping and re-building CB forks. Here’s the strip down one:
Luckily both my hex bolts cracked off no problems as I was dreading having to try the long reach fix!
My circlips were in bad shape and had disintegrated into a mush of rust so getting the fork seals out was tough. I had to just keep working round 360 degrees with a small pry bar until they slowly crept to the top and came out.
The fork oil was basically brown sludge. One fork had only a few millilitres of oil in it.
Cleaning front fork parts
I de-greased and blasted the re-usable parts. It took a bit longer than expected to clean the lower stantions as I couldn’t get inside to clean the old oil and grime out. When watching the YouTube clip about RaceTech emulators (below) the guy suggested a shotgun cleaning rod so I got one on eBay for £7. It worked well but I needed hot water and concentrated de-grease agent to get them properly clean.
If you do try this then wear a proper solvent rated mask. I was coughing for a few hours as I’d basically given myself a steam bath of caustic de-greaser!
The slight brown discolouring you see in some of the later photo’s is from the hot de-grease bath - see the white chemical reaction in the photo.
Smoothing out aluminium stantions
Once clean I decided to tackle some of the scuffs on the stantions. They weren’t bad and I wasn’t looking for perfection but I thought I’d try and smooth out the worst bits.
I used a Dremel to take the tops off and smooth down around the pits. I then used a polishing mop with heavy cut compound to blend it in. I then put it back through the blast cabinet to remove the compound and get a uniform scuffed aluminium finish ready for paint.
Spraying parts
I decided to spray the stantions satin black. I just scuffed them up with scotchbrite, masked them up with some string to hang them and wiped them down ready for primer. This Simonez Tough Paint says no primer needed but, being aluminium, I applied a few coats of etch primer then a few coats of satin black.
New front fork parts
The chrome fork tubes were pretty ruined and they seemed hard to find (part no. 51410-374-003). I trawled the web and found a new pair on eBay in Italy for £278 including postage. It turns out that pipes can be refurbished but as I've never done it before I wasn't sure how far gone they could be and come back “as-new”. Subsequent advice from experienced shock re-builders is not to refurb them as they don’t last as long. The refurb cost is around £120 per fork excluding postage so £278 for an OEM set seemed okay.
Once I’d got everything stripped I worked out what parts I needed to replace and ordered them from David Silver Spares. There’s more parts in there than I had originally thought. All together is was around £50 for oil seals, copper washers, circlips etc.
The CB550K has metal headlight brackets that covers the top part of the fork. This is where most of the rust was on the tubes. I decided to ditch them and the gaitor and replace with rubber dust seals from the CB550F. It’ll give the front end a cleaner look too.
Fork top caps & stem nut
The top caps were a little rusty and damaged so I decided to try and salvage them as they’re £24 each (or £15 for aftermarket). Not super expensive in the grand scheme of the build but I don’t like chrome so if spraying them aluminium looked okay then I’d use them. Unfortunately it didn’t work out - see pics below.
I wanted billet aluminium caps to match my Cognito Moto stem nut but they don’t make CB550 top caps which I’m a little surprised about. Joker Machine make a set but they’re over priced and a bit too bling for my tastes.
I found a Canadian company called Ripple Rock Racers that machine top caps (as well as other billet parts, custom exhausts etc) so I ordered a set for $75 (around £46 including shipping). There’s no import tax on items less than £135 from Canada but there was VAT at £4.74 and a ludicrous £8 Royal Mail handling fee.
That comes to £59 for great looking billet top caps that are over half the weight of OEM. They also do a matching stem nut which I would have bought if I’d found Ripple Rock before ordering one from Cognito. The owner Kemp is a nice guy and happy to help out. He’s making some real cool parts for CB SOHC bikes like an oil cooler & spin on filter.
Modifying the dampener rod for RaceTech cartridge emulators
For the valve emulators to do their job, you need to drill more holes into the OEM dampener rod. The instructions say 6 x 8mm holes for my forks. If the dampener rods are less than 17mm you only need 6 x 6mm holes and for thicker rods, it’s 6 x 8mm holes. I’m just above the line at 18mm but Matt advised 6mm holes. I noticed that the lower hole would be slightly blocked by the copper oil lock so I compromised with 6 x 7mm holes. The first two holes are from just widening the existing hole in the rod and drilling straight through.
Follow the instructions to space out the holes to maintain structural strength - 10mm between them, perpendicular (rotate 90 degrees) and above the stock hole.
You then have to de-burr to remove any sharp edges / loose metal. I made a bit of a mess of mine as I used the wrong tool to start with. It’s easy enough to do the front, but as you can’t get inside very easily, just watch that you don’t gouge out metal to the front of the holes while de-burring the back of the holes.
Take your time with this and get it right. I bought some CT-90 drilling fluid and set-up my mini pillar drill. I used a 4.8mm cobalt bit to pilot the holes then a HSS-G 7mm bit to drill the main holes. I’d use cobalt for both if doing it again.
To de-burr I tried a cobalt countersink tool but then switched to a small drill bit on my Dremel. Not my neatest work but I’m sure it’ll do the job.
Setting the RaceTech cartridge emulators & pre-load spacers
For my set-up, the DVS said blue springs and 2 turns of pre-load. They came with the blue springs fitted so I just needed to set the pre-load. There is documentation but as always, I find a YouTube video really helps. This one shows how to drill the dampener rod and set the emulator.
I found it easier to do in a vice so I could tighten the locking nut at the bottom without the adjuster screw moving. I also got some advice from Matt at RaceTech to superglue the adaptor rings to the emulators so the whole unit drops in together and seats on the dampener rod properly.
Although the DVS said I should use 15mm of pre-load, Matt recommended 25mm due to the 70KG springs. To work out the height of your spacer stack, first measure how far down the tube the top of the spring is - almost 41.5mm for me. Then measure the threaded section of your top cap - just under 24mm for me. To get 25mm of pre-load I needed a spacer around 42mm. The instructions say to have a washer above and below the spacer (plastic tubing). It’s tricky to get them both bang on but my stacks came to 41.6mm.
The washers that came with my kit all had slightly different thicknesses so I sorted them to have two stacks of equal thickness. I used the thickest at the bottom (between spring and plastic spacer) and two at the top. I kept the two thinnest washers in case I need to add some more pre-load. If I need reduce pre-load then I can remove one of the top washers.
Some of these images show smaller spacers. Initially I made up a 25mm spacer stack until Matt at RaceTech explained that it’s 25mm of spring compression. Lastly, make sure that your fork is fully extended when measuring how far down the spring is. I cut 4 sets of spacers getting this right!!
Re-assembling the front forks
With all the new parts sourced and set-up plus the old parts cleaned, painted & modified, it’s time to re-assemble. That said, when I unwrapped my new forks, they had a lot of surface rust on the inside. I used steel wool, my shotgun cleaning rod and some fork oil to clean them up. I then pushed through wads of blue roll a good few times and now they’re shiny again.
It’s pretty much a standard assembly as-per this video but the cartridge emulators add a few extra steps outlined below. Just make sure everything is super clean before assembling.
As my stantions are painted, there’s no way I was putting them in the vice so I assembled on the bench with towels down.
The OEM oil seals are tougher to get in than the easy fit ones in the video. You don’t need to push them all the way down, they just need to be tapped down below the line where the circlip sits. A little fork oil helps to lube the seals, both to get them in the stantions and to get the tubes in later on. Lesley helped me by pushing the tube in while I was tightening the bottom bolts and holding the forks when adding the oil.
The next job is the oil level. RaceTech gives their measurement in millimetres not millilitres i.e. the distance from the top of the oil to the top of the tube when fully compressed (bottomed out). For the CB550 its 130mm. The easiest way to do this is by a tube and syringe as-per this YouTube clip:
The tube I used was curved so I stuck my finger down the fork tube to hold it straight and get a true level. Remember to keep the fork as vertical as possible so the fluid is level. After the first fill, move the tube up and down to remove air pockets and get the oil in all the recesses. Remember to fully compress again to check the level / top-up - I added oil to one fully extended (after pumping the initial fill) and got oil everywhere when I compressed it - messy!
The last job is adding the cartridge emulators, springs, pre-load spacer (washer, plastic spacer then at least 1 washer) then put the top caps on. If you go with aluminium caps then watch for the swarf that comes off them (if you take them off multiple times) and carefully blow / wipe it off before re-assembling. Also, it’s worth using something like blue roll to save them getting marked by your socket.
Summary
All-in this was a pretty expensive part of the build at around £700 but the end result is fantastic. Cost difference aside, I still think it was the correct "in keeping with the theme" option, rather than a full GSX-R front end. Time will tell if it’s all set-up correctly but it’s relatively easy to tweak emulator settings by fishing them out with a long reach magnet.
The next job is finishing the brake rebuild and dual disc conversion.
Here’s some helpful reference links:
