For pretty much as long as I’ve ridden the TRX, I’ve wanted to do something about the front suspension. The forks, somehow, contrive to be weedy, bouncy, clattery, harsh, underdamped and overdamped. All at the same time. Looking on the bright side, well, the spring rate is about right for my weight, and they do keep the front wheel pointing in the right direction, but that’s about all they really had going for them. I’m probably being a little unfair, as the roads that I ride on around here are notoriously bumpy, and even well suspended bikes are soon tied up in tankslapping knots. Just avoiding the rapidly approaching dykes can be enough to keep your hands full at times. So, I had a few days off work this week, the bike was up on stands for a bit of routine maintenance, it was the perfect time to do something about it. A lot of TRX850 owners take a fairly radical approach to this problem, by just throwing the stock setup away, and replacing it with a set of forks from a YZF750. I briefly considered this, but ruled it out on the grounds that I fancied having a crack at fitting some cartridge emulators. If they don’t work, I can always throw them away, and then fit a fancy front end from a proper bike.
So, stage one then, was to determine what to buy. Racetech have always been the standard for cartridge emulation, but there’s a long lead time, and they’re pretty expensive. Enter the YSS PD fork valve. £63 a pair, the right size, in stock, delivered. That’ll do nicely. A litre of Rock Oil suspension oil completes the shopping list. “But what about the new seals?” I hear you ask. Well, yes, that would have been prudent. But, I put new seals in there when I rebuilt the forks, and it’s perfectly feasible to fit emulators without disturbing the seals, so I left them as is.
A couple of days later, a nice parcel turned up, and the valves dropped out:
I pottered out to the shed to fit things. This would have been much easier if it wasn’t 8 degrees below freezing, but at least I have a heater in the shed. Fitting emulators consists of five steps really:
- Drain oil, remove springs, spacers, damping rods.
- Shorten internals to allow new valves to fit.
- Open up oil flow in damping rods.
- Remove old damping gubbins.
- Refit everything.
So, pretty straightforward then. At first glance it seems like there’s a lot of complicated things to do, but break it all down, and it’s easy enough.
Step one passed without drama. The forks were dropped out of the bike, the caps removed, and then the springs and spacers came out with the aid of the magnet on a long stick. I turned the forks upside down in a bucket, and let the oil drain out. While that was happening, the damper retaining bolts were unscrewed from the bottom of the fork legs, and the dampers fell out with a nice clonk. Everything was cleaned up, and the forks just left in the bucket to complete draining.
Step two: making sure everything fits. Well, first step I guess is to measure the thickness of the valves. Out with the calipers:
I make that about 14.5mm, give or take. It’s not that critical. Now, we can either remove that amount of material from the spring, the damper rod, or the spacer. If I had a lathe, I’d probably remove that from the top of the damper rod, as that would make step four a lot easier (more of which later). Under no circumstances would I attempt to shorten the spring. Which leads to the spacer. Transferring the dimension to the spacer is trivial:
As well as not having a lathe, I don’t have any engineers blue either, so I just used a Sharpie, so the line scribed by the caliper was more visible. A quick appointment with Mr. Hacksaw later, and the spacers were about 14.5mm shorter. Again, a lathe would have made this easier. I really should start saving up.
Step three. Where were we? Ah, yes, increasing the oil flow. As standard, the damper rods have a pretty restrictive flow, which I think is responsible for the horribly overdamped high-speed damping in stock form. So, we’re going to replace a pair of 6mm holes with six 8mm holes. I chose to go this way, rather than just opening up the existing holes, as this bit of metal supports the entire weight of the bike under heavy braking. And I know I’m famous for saying “what’s the worst that can happen?” but in this case, I don’t even want to think about that. So, let’s mark up the damper rod where the new holes are to go:
Again, no engineers blue, so the Sharpie was pressed into service. I tried to keep things as well spaced as possible, with the middle set of holes at 90 degrees to the others. A whack with the centre punch, and a bit of drilling, and we’re left with this:
Which looks a lot more meaningful. What’s important here isn’t so much the drilling, as the cleaning up and deburring afterwards. We really don’t want to leave any swarf lurking in there to rip out the seals and get stuck in the valves later, so I spent quite a bit of time filing off the burrs internally and externally, and flushing the things out with solvents and compressed air. I’m resigned to the fact that they won’t be 100% perfect, but they’re as good as I’m going to get them without some very specialist equipment.
Step four: removing the existing damping gubbins. This is the most involved aspect of the job. The first stage of this is easy enough. Pop out the circlip from the damping adjuster:
With that removed, just pop the adjuster out of the damper rod. The little spring and ball-bearing used for the detent mechanism will fly out, so be careful you’re not looking too closely. Of course, this will land in a dark corner of the shed, never to be seen again. Here be spiders. With that removed, you now need to block up the five holes left at the top of the damper rod:
As mentioned earlier, if I had a lathe, I’d simply have taken 14-15mm off the top of the damper rod, which would have removed the four small holes used by the damping adjuster detent. But I don’t, so I had to think of another way. It’s perfectly feasible to sleeve the inside of the rod, and I considered using the old adjusters to do this, but they would have needed lots of machining to remove the core of the casting, and I just don’t have access to that kind of machinery. So, I cleaned everything up as best I could, and broke out the MIG and angle grinder:
Now, it’s worth remembering that in the hands of the right person, an angle grinder can be a precision tool. Looking at the above, it’s safe to say that person isn’t me. Anyway, again, this isn’t brain surgery – it just needs to be clean, and oil tight. Again, give everything a good clean in solvent to get rid of any swarf left behind by the grinding. Also worth mentioning that I cleaned things up a bit more with a Dremel to get into all the nooks and crannies. Finally, (and this really should have been covered in step two), I chopped the adjuster rods off near the top:
This is purely to stop them clouting the new valves when everything is buttoned back together. Which brings us on to:
Step five: putting everything back. Again, give everything a good clean, then put the damper spring and little red plastic seal back on the damper rod. Drop it into the fork, and refit the retaining bolt. Prepare to say goodbye to the little valves:
Drop the valves on top of the damper rods, with the long bit of the adjuster on top. Refill with oil (I used 10 weight), and the book figure is a 130mm air gap, compessed, with no spring. Now, when pumping the forks to expel any air from the damper mechanism, chances are that you’ll push the valves up out of their seat, and they’ll land again at a funky angle. This isn’t what we want at all, so spend some time with the spring and dampers fitted, bouncing things up and down, checking that the caps will fit without undue pressure, to ensure that the valves are seated correctly.
And that’s it really. Any difference? No idea at the mo. There’s eight centimetres of snow outside, and no way I’m going for a test ride. So much for the rites of Spring.