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Bleeding forks

Posted: Thu May 10, 2007 8:09 am
by sproggy
The manual gives this final instruction for after you've put new oil in the forks:

"Bleed telescopic forks under zero load."

What's zero load? Front of bike lifted off ground, forks fully extended? Or bike sitting on the ground upright with no rider on board? Obviously this makes a difference to the amount of air left in the forks, and therefore to the (admittedly fairly minimal) damping characeristics of the forks themselves. Anyone know what 'zero load' is supposed to mean?

Posted: Thu May 10, 2007 9:07 am
by bigblackfalco
If you've got centerstand fitted, I'd suggest that it just sits on that lightly on the front wheel.
if no centrestand, then (as you say) just with no rider onboard. Try to make sure the bike is as upright as possible so that the fork legs are equal amounts into sliders.
The issue is ensuring that there is not too much air trapped in the fork legs as this will cause a harsh ride and also bring early demise of the fork seals due to the increase in internal pressure.
Bailey.

Posted: Thu May 10, 2007 9:43 am
by sproggy
bigblackfalco wrote:If you've got centerstand fitted, I'd suggest that it just sits on that lightly on the front wheel.
No centre stand.
bigblackfalco wrote:if no centrestand, then (as you say) just with no rider onboard. Try to make sure the bike is as upright as possible so that the fork legs are equal amounts into sliders.
It's on a paddock stand so that's as level as it needs to be.
bigblackfalco wrote:The issue is ensuring that there is not too much air trapped in the fork legs as this will cause a harsh ride and also bring early demise of the fork seals due to the increase in internal pressure.
Bailey.
That was my worry. When I first put it all back together the first time I bled the forks with the front of the bike lifted (maximum amount of air inside) which was my interpretation of 'zero load' and on the first ride some oil seeped past the dust seals. That was with only 170ml of oil per fork. The oil may have got there just by being in the wrong place during reassembly, though. Last night I put the missing 320ml of oil into each fork (using a syringe through the bleed valve hole - didn't fancy taking them off the bike again), pumped the front end a few times and put the valves back in with the front wheel on the ground. A brief test ride on a very bumpy road didn't cause any further leakage of oil and the bike feels OK so hopefully it's sorted now.

Cheers.

Posted: Thu May 10, 2007 10:59 am
by Ade B
I made a total pigs ear of a fork seal replacement several thousand miles ago - I left the forks on the bike and ended up with some serious guestimation on the amounts of fork oil in the LH leg.

The seal is still good and I havn't really noticed much affect on the handling - which is not to say there isn't one.


Ade.

Posted: Thu May 10, 2007 4:50 pm
by gus
Just to point out, early forklegs have 170 ml per leg.Later models have the greater oil capacity.
Just hold the bike upright and level and off any stands,then bleed away.
gus