Tuesday, May 17, 2011

KTM 50 Mini Adventure - Forks.

There's a certain lack of damping on this bike. The rear shock is knackered, along with its bushes; but the forks, although good in appearance, were out of sync. The one seemed fine - pushed down easily and returned slowly, spot on. The other felt like it had no oil.

So, first things first, whip the caps off and drain them.

They don't always unscrew as easily as this. I cheated - I'd already undone them with an airgun. If you're struggling to loosen them, fit them back into the yokes (triple clamps) and tighten the lower section. Leave the top yoke loose and you should now be able to undo the fork top nut.

Fork top nut out to reveal a plastic spacer. Not sure if this is genuine or not. Seems like a long spacer or a short spring! Anyway, both forks had oil in them so obviously that's not the problem. 

Out with the spring, then a 6mm Allen key to remove the bottom bolt.

Then we can remove the damper assembly with the stanchion. The aluminium collar on the end of the damper tube just slides off, and the damper rod itself can be dropped out through the opposite end of the stanchion.

And finally, we see the problem, or not. The plastic "piston ring" is missing from the sleeve, allowing the oil to bypass, but KTM only list one. It should fit into the groove on the white plastic section at the end of the damper rod, but maybe only one leg needs it. We're going to get hold of another piston ring and fit it to see how it performs. 

From what I can gather online, 110 ml of oil per fork is required and, by the feel of the other one, it's just the job.

There we have the basic, conventional fork stripped down. Very easy to work on and diagnose so don't be afraid to get stuck in.

Sorry for the blurriness of some of the photos, that particular photographer has now been sacked!