I have a 1980 Darmah which was rebuilt around 7 years ago and hasn't been used since. The forks were very 'stiff' with little suspension or damping in evidence at all. I've checked that the wheel is fitted correctly and the legs are not twisted. When I drained the oil, there was around 180cc in each leg, but very discoloured and quite viscous - possibly 20 grade or more. The spring lengths were similar, but I can't find what the spec is, so have no idea if they are right or not. The spacers below the top nut which are supposed to be 35mm long were actually 55mm but had been marked by someone at 35mm, as though they had meant to cut them down. I cut them to the correct length and refilled the legs with 10 grade fork oil and they are much better, but still not great. The travel seems about right (can't be certain as the brakes are too weak currently to bottom them out- another job) but they don't really iron out the bumps. I'm thinking to try lighter oil and possibly removing the spacers altogether - the forks would still be slightly loaded without them, but any suggestions or advice would be appreciated.
185cc is correct tube length should be 600mm Forks should be fully extended with the weight of the bike on them ( not the rider) stiction is a problem with these forks and so is spring length if the springs have gone soft. If you dont want to cut tubes to give the correct preload, 2p coins do just as well
Also dont forget to expel the air in the tubes or you will get a lock. slacken the screws in the top nuts and bounce the forks as far as you can then tighten the screws again
Where am I measuring this from and to? The length from the top of the fork to the bottom is 800mm. Mine has 26mm compression with just the bike's weight, so I'm guessing the springs have had it. What do you recommend to replace them with? Are the YSS progressive springs any good?
As an update to this, having stripped the forks and rebuilt them, I found that the expander ring which sits behind the damper piston ring was missing from one leg altogether. Having cleaned everything and replaced this missing part, the forks now work better, but they are still far from great. I haven't managed to source any suitable replacement springs. I tried some YSS progressive items, but they wouldn't fit in the spring guides and trying to fit them without is a non-starter as they just twisted up inside the legs and made a dreadful noise scraping the sides. I'm pretty sure that losing one of the two oil seals would help matters, as would polishing the inside of the stanchions where the sliders move, but I still need to find some springs which will fit. If anyone has any suggestions, I'd really appreciate it. Also, the damper pistions were installed as they are shown on the parts diagram - with the crown pointing up, but I've see a few instances where the piston is facing down in the leg instead. I'm not sure what, if any difference this would make, but does anyone know which way it should be?
