When I think back to my early travels, the idea of doing anything more than just jacking up the shock to carry the load never occurred to me. With suspension, it has to be pretty terrible for you to notice, and for that to happen – or for good stuff to show it’s worth – you need to be either riding pretty fast, or hammering over rough terrain. If you don’t do much of either or don’t have up to a grand to spare (or have good, fully adjustable forks) it’s probably not worth it. But for under £100 it’s possible to improve a non-adjustable fork’s damping action. And my Serow could do with some of that.
Can’t be bothered to read another word, but still curious? Watch the 12-min vid at the bottom
On our H.A.T recce in Morocco last November (left), right off the bat the Serow’s front end was all over the place on stony trails. Notably worse than other bikes I’d ridden lately. It never bottomed out and the back end wasn’t sagging, so I presumed it was a combination of too stiff front tyre and especially poor damping, that inscrutable function which controls spring rebound.
‘Spend a grand plus taxes on a full, US-imported Cogent front and rear Serow set up‘ they said. ‘Night and day or your money back!’ Cogent also did just a fork kit with emulator valves, replacement springs and oil for around $400. I didn’t need a spring or oil, just valves, and would end up with better, but still unadjustable forks. Next stop were Race Tech Gold Valves for $230 (FEGV 3311). Still quite a lot with import tax and all. You’ll find much online chat about the pros and cons of Cogent vs Race Tech emulators.
Long story short, widely UK-sold YSS also do a range of emulator valves for just 90 quid (below). They’re not gold, but as I needed a new fork seal anyway, it seemed worth a shot to DIY, even though I’d never taken forks apart before.
I’d heard of emulators but wasn’t really sure what they were. Turns out they’re easily fitted valves which enable conventional, archaic damper rod forks to ’emulate’ supposedly superior cartridge forks (Cart-what? For another time).
The valve (above left) is an adjustable spring loaded plunger which sits between the fixed damper rod and the fork spring (right). As forks compress, oil is pushed through the valve, opening the spring which is otherwise closed. Oil flows through progressively relative to force, compared to crude, static conventional damping rods with just a couple of drilled holes controlling flow. The vid below made Race Tech installation on an XT500 look relatively easy.
You need a set with a diameter that slips snuggly down your fork tube. For a Serow it wasn’t possible to find that info online, and guessing from the fork tube outer ø is just that (I now know…). The best way to verify your fork tube’s internal ø is to undo the fork cap, lift out the spacer/spring, and measure ID with some verniers. On the Serow fork ID was ~30mm – not my 31mm estimate. The 31s got sent back for exchange but never made it. By chance I found some used next-size-down YSS 29s on ebay for half price. Weeks passed by for all these fascinating events to occur.
If only it was all like the slick vid below in a well lit and superbly equipped workshop with dinky music tinkling in the background. Whip out the springs, tip out the effortlessly unscrewed rod, pop in the new valves and reverse the rest before damping progressively into the sunset. My damper rods didn’t slip out nicely, so the entire fork leg needed to be disassembled.
Unless going Cogent, you need to get your hands on the damper rod because additional holes must be drilled for oil to pass unfettered up to the new emulator valve. A hex bolt at the base of the fork secures the damper rod inside the lower fork. But they’re notoriously tricky to remove because it’s like trying to undo a bolt from an unseen nut without any means of restraining the nut.
‘Get a rattle gun’ I was advised (left; pneumatic impact driver), to ‘shock’ the allen bolt from the damper rod to which it’s been seized for the last 15 years.
I had a compressor tank and found a 25 quid rattler on ebay – ker-ching. But air gun shock therapy wasn’t working. The rod was spinning inside – as you’d expect. A ha, I thought, I will ram a whittled stick in the other end to stop the rod spinning, lock it off with some Moles (below left), then apply rattle. That worked – eventually, but on reassembly it didn’t, so I deployed the ‘broom trick’ I’d seen mentioned online. Same idea: slide it down the fork tube and press against to the damper rod, then pull the trigger. Long arms needed. All this seemed a bit less faff than entirely reassembling the fork (as in the vid) to add tension to the rod for removal/refitting.
Much faffing later, I had the forks in bits by which time I realised I could have fitted the new fork seal myself, not at the LBS.
To maintain your fork spring effective length/preload (FSEL/P) and not void your insurance, you need to saw off the height of the valve’s body – about an inch – from the spacer tubes so it all fits back together again (below). A fairly easy job even I find hard to mess up.
Next job was drilling several extra flow holes in the damper rods which normally have just a couple near the bottom. Like much of the Serow, this is 1970s technology, maybe older, but I suppose it works well enough. More holes let the oil move quickly up to the sprung emulator valve which controls the variable flow. Another thing I learned: on my forks the drilled rods pass through a close-fitting nylon collar at some stage, so any protruding burrs from the drilling lock the action so need to be ground right off to slide through the collar smoothly.
By now Christmas had come and gone, so had New Year and there were already chocolate eggs in the shops. But I was getting close and the forks slid smoothy in and out, like they should. I did the ‘broom trick’ as mentioned above to tighten the rods back onto the fork leg with the air gun, and was so amazed it worked, I stopped right there and took the rest of the day off before another cock up kicked me in the nuts.
“Refitting is the reverse sequence to removal.” to quote M Haynes, and amazingly, only one bolt had escaped in the weeks it took to complete a simple one-day task. But let’s snatch a bit of positive: I’d leaned about fork internals. Having avoided fork disassembly all these decades, I can now see they’re not so complicated. Amazingly, a simple circlip appears to hold the two parts of a leg together. Undo that and whack the two sections apart like a Christmas cracker to get to the seal or damper rod. Along with rod removal, refitting a seal without damage without the correct slide tool is probably the hardest job.
Deciding on fork oil weight and volume/height is another chance to tie yourself in knots of self doubt. I found several values online for the ‘XT250’ until I realised just measure the volume of watery, brown muck which poured out of the non-leaky leg – 350cc. In fact I poured in just 300cc of 10W, thinking it’d be easier to add more if something felt very off, rather than try and suck some out.
By the time I reached this climactic stage, the Serow’s previous owner got in touch asking whether I might like to sell it back. Someone must have told her I was a serial bike quickshifter! With Morocco snowed out and me elsewhere this winter, a deal was made, a date was set. I topped up the rear tubeless tyre and took the Serow out for one last ride along Purbeck’s flooded lanes.
The forks felt the same – fine on normal roads, as before. No great surprise. I’d need to find a rocky climb to see if the front responded any better, but right now what few local lanes I knew around here where probably knee-deep in mud and rotting leaf sludge.
So I puttered merrily around the Purbeck Hills I usually cycle in the summer and tried to think what could replace the agreeable Serow. As I did so the aroma of mud evaporating off the hot pipe took me right back to my earliest days dicking about on Surrey wastelands with ratty trail bikes (left).
What bike was as light, low saddled, semi-tubeless, economical, started on the button and came with racks and a screen? My CRF300L a couple of bikes back probably fitted the bill, but look at the huge amount of spending and work it required to reach that stage. I guess that’s why these old Serows hold their value.
Adventure Motorcycling Handbook 