I know we have discussed mid valves a number of times, but I have a few questions you all may be able to help with and at least should be interesting to discuss.
First, I just finished rebuilding my 01 yz426 fork and found the midvalve shims to be quite worn and a couple of the shims were bent. I use a 2 stage base valve stack, stock midvalve config, and I replaced the cylinder valve with bottoming cones. I weigh 190 lbs and ride fairly agressively (intermediate to slow pro) in Mx as well as a bit of offroad.
Anyway, back to my question Why do you think the valves bend? Is the stack too light to support the shims under high load, or is it just normal wear?
My feeling is that it has something to do with the floating nature of the stack. Most stacks are compressed and held fixed in the center so they have some additional stability and the outside flexes up. On the midvalves since they float I think as the outside of the shims flex up the inside is able to flex down thus bending them more and causing them to form a slight funnel shape. This added degree of movement may contribute to the shims bending and staying that way over time.
Second question
How can we fix this?
I was thinking that pinching them down on the piston (like a traditional stack) could add stability, but you loose the float. Could you compensate with ligher valving or a 2 stage setup with a fairly thick transition shim?
Or could you build a floating midvalve which is clamped together on a tube with a shoulder, threaded on the outside with a locknut, where the entire tube floats and the piston is recessed in the center to clear the shoulder and allow the shims to seal on the rebound stroke? This would add stablilty to the stack while still allowing float.
One last question on valving.
My bike works very well on the track(as long as the midvalves aren't bent) and it is also pretty good off road. But, off road it tends to deflect a bit on rocks, especially while climbing. I use fairly stiff springs .48 front with 3mm preload and 5.6 rear, and they seemed to actually make the initial travel a bit smoother and I don't drag pegs in turns as much. Do you think this deflection is due to the springs, stiff high speed valving, stiff low speed valving, or something I haven't considered. Is there a way to minimize this without revalving every time I ride in different conditions, since I ride mostly MX and this is the only place the current setup bothers me offroad. Maybe I just have to live with it.
Thanks,
Jason
First, I just finished rebuilding my 01 yz426 fork and found the midvalve shims to be quite worn and a couple of the shims were bent. I use a 2 stage base valve stack, stock midvalve config, and I replaced the cylinder valve with bottoming cones. I weigh 190 lbs and ride fairly agressively (intermediate to slow pro) in Mx as well as a bit of offroad.
Anyway, back to my question Why do you think the valves bend? Is the stack too light to support the shims under high load, or is it just normal wear?
My feeling is that it has something to do with the floating nature of the stack. Most stacks are compressed and held fixed in the center so they have some additional stability and the outside flexes up. On the midvalves since they float I think as the outside of the shims flex up the inside is able to flex down thus bending them more and causing them to form a slight funnel shape. This added degree of movement may contribute to the shims bending and staying that way over time.
Second question
How can we fix this?
I was thinking that pinching them down on the piston (like a traditional stack) could add stability, but you loose the float. Could you compensate with ligher valving or a 2 stage setup with a fairly thick transition shim?
Or could you build a floating midvalve which is clamped together on a tube with a shoulder, threaded on the outside with a locknut, where the entire tube floats and the piston is recessed in the center to clear the shoulder and allow the shims to seal on the rebound stroke? This would add stablilty to the stack while still allowing float.
One last question on valving.
My bike works very well on the track(as long as the midvalves aren't bent) and it is also pretty good off road. But, off road it tends to deflect a bit on rocks, especially while climbing. I use fairly stiff springs .48 front with 3mm preload and 5.6 rear, and they seemed to actually make the initial travel a bit smoother and I don't drag pegs in turns as much. Do you think this deflection is due to the springs, stiff high speed valving, stiff low speed valving, or something I haven't considered. Is there a way to minimize this without revalving every time I ride in different conditions, since I ride mostly MX and this is the only place the current setup bothers me offroad. Maybe I just have to live with it.
Thanks,
Jason
