First off, my bike is a 98 KX250 (43mm KYB's). Right now the forks are apart to change the bushings and fork seals (that's what it turned into anyway...). I've been lurking in the Suspension forum somewhat and some of the stuff is confusing. Now that I have the forks apart I can more easily see some things. Let me see where to begin asking questions...
Is there a way to determine what the spring rate is? What are the units they are rated in? If they are not marked in any way, how hard would it be to actually test them, with at least enough precision to know if I need new ones (although right now I can't really afford new springs, I'd like to know for when I can)?
I recently learned that the valving refers to the shim stack. I just took apart one of the base valves and found the shim stack... it's hard to believe that those little shims have such a big affect on the suspension action. I don't really feel confident messing with those right now, but it's neat to see where they are and how they work. Is there a mid-valve in addition to the base valve? I think I have heard there is - if so, is it the small bulge on the damping rod right under the big white plastic spacer? Or is it on the bottom of the piston? Looking up the damping tube (I don't know what it's official name is), it looks like there may be some shims up there...
I think I now understand the basic consruction and operation of the forks. The two big outer tubes are for mechanical rigidity and act to some extent as an oil resevoir. The inner "set" (damping rod, and what I'll call the damping tube) are the actual "shock absorbing" elements - the piston forces oil to flow in the bottom of the damping tube and through the base valve. It appears that the base valve regulates the flow of the oil from the four ports on the perimeter to the inside of the damping rod - is this correct?
What is the rod inside of the damping rod that can move freely? It seems that these (at the least a short on top of the longer one) rise up out of the damping rod when I unscrew the fork cap and let the fork start to compress. My guess is that it has to do with the clicker in the fork cap... but I don't know. Does the oil flow through this all the way from the base valve or from the midvalve?
I feel that I can understand the seperate oil regulation stages (valving, piston, etc) but don't have a complete understanding of the whole oil flow in the fork. It seems that the outer fork sections (only the upper tube?) are like an oil resevoir, and the oil gets pumped back into the resevoir during compression through the holes in the long hex nut on the top of the damping rod, right under the fork cap. Does the oil re-enter the system through the bottom of the damping tube, right under the base valve?
How does the clicker on the bottom of the base valve assembly work? Which oil flow path does it control?
Last time I replaced the fork seals I messed up the bushings a bit by pulling out the oil seals by yanking on the lower tube without heating around the oil seal. These are just the outer bushings, right? It seems to me (I haven't pulled out the oil seal and seperated the two fork tubes yet) that the inner bushings are between the lower fork tube and the damping tube, so those shouldn't be damaged.
Last time I had the forks apart I refilled them with ATF. What weight is this approximately? I read recently that it may be a bad idea in these forks because it makes them harsher than they should be... what weight oil should I go with? It doesn't feel really harsh, but my arms do pump up pretty quick when
on an MX track (due more to me being out of shape than suspension, I think).
Would it be pretty cheap to just send the valves to a suspension tuner like Jeremy Wilkey and have them modify the shim stack? I can't imagine it would take more than 10 minutes or so with everything already apart... If I knew what I was doing I've got it all apart and could do it easily, but I don't even know exactly what to change or how I want it - as they say, you don't know any better suspension than what you have experienced.
Is there anything to prevent hard bottoming? I don't see any rubber bumpers in there...
I guess that's enough questions for now, and a long enough post. If you can answer any of the questions (and you have read this far), please do. I want to understand this stuff.
Thanks,
Andy
Is there a way to determine what the spring rate is? What are the units they are rated in? If they are not marked in any way, how hard would it be to actually test them, with at least enough precision to know if I need new ones (although right now I can't really afford new springs, I'd like to know for when I can)?
I recently learned that the valving refers to the shim stack. I just took apart one of the base valves and found the shim stack... it's hard to believe that those little shims have such a big affect on the suspension action. I don't really feel confident messing with those right now, but it's neat to see where they are and how they work. Is there a mid-valve in addition to the base valve? I think I have heard there is - if so, is it the small bulge on the damping rod right under the big white plastic spacer? Or is it on the bottom of the piston? Looking up the damping tube (I don't know what it's official name is), it looks like there may be some shims up there...
I think I now understand the basic consruction and operation of the forks. The two big outer tubes are for mechanical rigidity and act to some extent as an oil resevoir. The inner "set" (damping rod, and what I'll call the damping tube) are the actual "shock absorbing" elements - the piston forces oil to flow in the bottom of the damping tube and through the base valve. It appears that the base valve regulates the flow of the oil from the four ports on the perimeter to the inside of the damping rod - is this correct?
What is the rod inside of the damping rod that can move freely? It seems that these (at the least a short on top of the longer one) rise up out of the damping rod when I unscrew the fork cap and let the fork start to compress. My guess is that it has to do with the clicker in the fork cap... but I don't know. Does the oil flow through this all the way from the base valve or from the midvalve?
I feel that I can understand the seperate oil regulation stages (valving, piston, etc) but don't have a complete understanding of the whole oil flow in the fork. It seems that the outer fork sections (only the upper tube?) are like an oil resevoir, and the oil gets pumped back into the resevoir during compression through the holes in the long hex nut on the top of the damping rod, right under the fork cap. Does the oil re-enter the system through the bottom of the damping tube, right under the base valve?
How does the clicker on the bottom of the base valve assembly work? Which oil flow path does it control?
Last time I replaced the fork seals I messed up the bushings a bit by pulling out the oil seals by yanking on the lower tube without heating around the oil seal. These are just the outer bushings, right? It seems to me (I haven't pulled out the oil seal and seperated the two fork tubes yet) that the inner bushings are between the lower fork tube and the damping tube, so those shouldn't be damaged.
Last time I had the forks apart I refilled them with ATF. What weight is this approximately? I read recently that it may be a bad idea in these forks because it makes them harsher than they should be... what weight oil should I go with? It doesn't feel really harsh, but my arms do pump up pretty quick when
on an MX track (due more to me being out of shape than suspension, I think).
Would it be pretty cheap to just send the valves to a suspension tuner like Jeremy Wilkey and have them modify the shim stack? I can't imagine it would take more than 10 minutes or so with everything already apart... If I knew what I was doing I've got it all apart and could do it easily, but I don't even know exactly what to change or how I want it - as they say, you don't know any better suspension than what you have experienced.
Is there anything to prevent hard bottoming? I don't see any rubber bumpers in there...
I guess that's enough questions for now, and a long enough post. If you can answer any of the questions (and you have read this far), please do. I want to understand this stuff.
Thanks,
Andy
