Post by randall on Jan 9, 2013 6:02:51 GMT -6
Further on with my 2006 Diamo Velux restoration, after sorting all the engine and transmission issues, my attention has turned to the front end. First thing I did was add balancing beads to the tires which made the world of difference, checked the tightness of the tree bearings, ok there, but of course with these issues out of the way it more clearly reveals all the other stuff that's wrong! So, on to the forks.
After scouring all the available service info on this bike, I have not been able to find a level or capacity or viscosity spec for the fork oil. Just isn't out there. But, researching bikes of similar size and weight, I found capacities ranging from 100ml to 150ml. notably the Benelli Adiva, nearly the same bike, calls for 140ml.
Presently, the front end seems to behave ok with road swells, speed bumps, etc., and anything that doesn't require the fork to move too quickly. But any washboard stuff, sudden holes, or high speed driving I can tell the fork is just not responsive enough and I'm getting instability. Hitting a bit of washboard at 50mph is presently a scary experience.
I pulled the forks off, removed the top caps and springs and measured the oils level. They were not matched. In fact off by about half an inch. Poured and pumped out all the oil and found 100ml in one and 70ml in the other. Also, what was in there was very thick, like maybe 40 or 50 weight. On a side note, the springs are nicely exactly the same length.
With no good data to help me out, I'm now doing this empirically. Decided to start out with some synthetic ATF since I had that on hand. It's amzoil which is about 7.5wt I believe. I added 125ml to each fork, bled it through well, and with no spring and the tube fully compressed I'm measuring 1-3/4 inch from the top of the tube to the oil level. So i at least now have a benchmark, a starting point. Buttoned the forks back together and by hand I can tell that they are much smoother, not as heavily damped. I'll be reassembling this morning and test riding sometime today.
My question is, I have to think that there's a good scientific way of determining fork oil level in the tube. Like a simple formulae that says if the tube is x diameter, y travel, etc., then what should the volume of the compressible air cavity be? Just thought I'd throw this out there and see if anyone had any insights on this.
After scouring all the available service info on this bike, I have not been able to find a level or capacity or viscosity spec for the fork oil. Just isn't out there. But, researching bikes of similar size and weight, I found capacities ranging from 100ml to 150ml. notably the Benelli Adiva, nearly the same bike, calls for 140ml.
Presently, the front end seems to behave ok with road swells, speed bumps, etc., and anything that doesn't require the fork to move too quickly. But any washboard stuff, sudden holes, or high speed driving I can tell the fork is just not responsive enough and I'm getting instability. Hitting a bit of washboard at 50mph is presently a scary experience.
I pulled the forks off, removed the top caps and springs and measured the oils level. They were not matched. In fact off by about half an inch. Poured and pumped out all the oil and found 100ml in one and 70ml in the other. Also, what was in there was very thick, like maybe 40 or 50 weight. On a side note, the springs are nicely exactly the same length.
With no good data to help me out, I'm now doing this empirically. Decided to start out with some synthetic ATF since I had that on hand. It's amzoil which is about 7.5wt I believe. I added 125ml to each fork, bled it through well, and with no spring and the tube fully compressed I'm measuring 1-3/4 inch from the top of the tube to the oil level. So i at least now have a benchmark, a starting point. Buttoned the forks back together and by hand I can tell that they are much smoother, not as heavily damped. I'll be reassembling this morning and test riding sometime today.
My question is, I have to think that there's a good scientific way of determining fork oil level in the tube. Like a simple formulae that says if the tube is x diameter, y travel, etc., then what should the volume of the compressible air cavity be? Just thought I'd throw this out there and see if anyone had any insights on this.
