Hi Guys,
With the release of the new Domain and the Yari RC still being frequently speced on bikes I've been sucked into the black hole of Motion Control (MoCo) DIY tuning. I currently have 2 Yari at home (Hardtail and GF bike) and before testing my theory i'd like to run it by you so I don't render those forks useless for no reasons.
I base my theory after reading following ressources:
- Understanding of original MoCo: https://ridemonkey.bikemag.com/threads/tuning-blackbox-speedstack-in-boxxer-wc-team.166577/
- Tuning of the more recent versions: https://www.mtbr.com/threads/super-yari.1069974/
- Modification of the MoCo by a german tuner: https://www.bike-magazin.de/freeride/test/80-euro-federgabel-tuning-pimp-my-yari
- German DIY mod: https://radtechnik.2ix.de/yarituning.php
- English speaking DIY mod: http://www.supercross-online.de/Z/Yari_MotionControl
So MoCo is basically an orifice damper with a poppet valve.
First thing you can do is to reduce the amount of MoCo movement before it opens the poppet. Back in the days it was done by a nyloc nut, nowadays you do that with little spacers. This helps to reduce spiking, it isn't a terrible place to start as it is reversible and really easy to do. I also retains the possibility to adjust compression bleed (LsC) but you have zero control over your damping curve. It might be enough for many people tho. It might be enough for me too but I have compulsive tinkering syndrome so I can't leave potential when I see some.
Now next is what is done by Anyrace and somewhat similarly by Radtechnik, they increased the LsC ports to have enough flow for it not to spike and controlled the flow with a shim stack. This allows you to have much more control over your damping curve since you just have to modify your stack depending on your needs. One problem is that you don't have control over low speed compression (bleed) as you need to leave the sawblade fully open, if you don't you would be back to orifice damping as the shim stack wouldn't do anything if inline with a bottleneck. Same problem as the old boxxer WC and the Speedstack. So any adjustment to LsC have to be done by stack modification which is not practical.
Finally SX-online solution for which you basically use 2 of the LsC holes for shim damping and the last hole is used for LsC adjustment. Main issue with this one is that the shims get unequally loaded. I am not sure if this is a problem in real world but this is why I came up with my idea as this solution mostly solves all the problems.
Now what I propose is to create a completely independent shim circuit and keep the original LsC circuit mostly untouched.This would offer a proper bleed adjustment (ultra low speed) via the original LsC circuit, Low to High speed compression through the shims stack and if you need extra digressive damping the possibility to space the poppet valve for blow-off. To achieve this I propose to drill 3 holes in the 3 ridges that are not used in the MoCo head. The hole would have to be drilled at an angle in order to use a shim that would not cover the LsC circuit but still exit outside of the Sawblade so the shim circuit would not be impacted by the LsC adjuster. Aside from the drilling the LsC hole would have to be chamfered so would the Shim circuit holes on their entrance side. This this means that the oil flow will not be optimal as it won't be straight but I think it is negligible and as long as the chamfers allow to keep the orifice surface it shouldn't be a problem. Because I try to keep the LsC circuit close to its original state my solution would use some face shims of 20mm OD likke Radtechnik instead of the 22mm used by SX-online.
Some pictures to illustrate the idea (cred: Radtechnik), in red the new holes for the Shim circuit, in black the original LsC holes, in yellow the chamfers to allow LsC circuit to not be obstructed by the 20mm face shim (used in this picture), in green the chamfer at the entry of the shim circuit to not be restricted by the sawblade.
To dive a bit deeper into the theory, SX-online seems satisfied with a LsC circuit of 6.4mm² and a Shimed circuit of 19.2mm². My solution should offer slightly more flow with LsC at 13mm² (original surface) and with a drilling of 3mm a shimed circuit of 21.2mm². While the extra LsC surface if probably useless and will need to be at least half way closed, having the option is good. Having extra shim circuit surface should allow for more tuning possibility of the HsC via the shimstack with less risk to hit the maximum flow. If this was to happen you could still control it with the poppet valve spacing. If more shim circuit flow is need one could go with SX-Online solution and simply drill some 3.5mm holes in (some of) the blank ridges as I doubt the would be enough room on the ridges to drill bigger than 3mm and remain within the 20mm face shim diameter.
What do you guys think ? Am I out of my mind ? Do that sound solid enough so I should order some shims and take the dremel out ?
With the release of the new Domain and the Yari RC still being frequently speced on bikes I've been sucked into the black hole of Motion Control (MoCo) DIY tuning. I currently have 2 Yari at home (Hardtail and GF bike) and before testing my theory i'd like to run it by you so I don't render those forks useless for no reasons.
I base my theory after reading following ressources:
- Understanding of original MoCo: https://ridemonkey.bikemag.com/threads/tuning-blackbox-speedstack-in-boxxer-wc-team.166577/
- Tuning of the more recent versions: https://www.mtbr.com/threads/super-yari.1069974/
- Modification of the MoCo by a german tuner: https://www.bike-magazin.de/freeride/test/80-euro-federgabel-tuning-pimp-my-yari
- German DIY mod: https://radtechnik.2ix.de/yarituning.php
- English speaking DIY mod: http://www.supercross-online.de/Z/Yari_MotionControl
So MoCo is basically an orifice damper with a poppet valve.
First thing you can do is to reduce the amount of MoCo movement before it opens the poppet. Back in the days it was done by a nyloc nut, nowadays you do that with little spacers. This helps to reduce spiking, it isn't a terrible place to start as it is reversible and really easy to do. I also retains the possibility to adjust compression bleed (LsC) but you have zero control over your damping curve. It might be enough for many people tho. It might be enough for me too but I have compulsive tinkering syndrome so I can't leave potential when I see some.
Now next is what is done by Anyrace and somewhat similarly by Radtechnik, they increased the LsC ports to have enough flow for it not to spike and controlled the flow with a shim stack. This allows you to have much more control over your damping curve since you just have to modify your stack depending on your needs. One problem is that you don't have control over low speed compression (bleed) as you need to leave the sawblade fully open, if you don't you would be back to orifice damping as the shim stack wouldn't do anything if inline with a bottleneck. Same problem as the old boxxer WC and the Speedstack. So any adjustment to LsC have to be done by stack modification which is not practical.
Finally SX-online solution for which you basically use 2 of the LsC holes for shim damping and the last hole is used for LsC adjustment. Main issue with this one is that the shims get unequally loaded. I am not sure if this is a problem in real world but this is why I came up with my idea as this solution mostly solves all the problems.
Now what I propose is to create a completely independent shim circuit and keep the original LsC circuit mostly untouched.This would offer a proper bleed adjustment (ultra low speed) via the original LsC circuit, Low to High speed compression through the shims stack and if you need extra digressive damping the possibility to space the poppet valve for blow-off. To achieve this I propose to drill 3 holes in the 3 ridges that are not used in the MoCo head. The hole would have to be drilled at an angle in order to use a shim that would not cover the LsC circuit but still exit outside of the Sawblade so the shim circuit would not be impacted by the LsC adjuster. Aside from the drilling the LsC hole would have to be chamfered so would the Shim circuit holes on their entrance side. This this means that the oil flow will not be optimal as it won't be straight but I think it is negligible and as long as the chamfers allow to keep the orifice surface it shouldn't be a problem. Because I try to keep the LsC circuit close to its original state my solution would use some face shims of 20mm OD likke Radtechnik instead of the 22mm used by SX-online.
Some pictures to illustrate the idea (cred: Radtechnik), in red the new holes for the Shim circuit, in black the original LsC holes, in yellow the chamfers to allow LsC circuit to not be obstructed by the 20mm face shim (used in this picture), in green the chamfer at the entry of the shim circuit to not be restricted by the sawblade.
To dive a bit deeper into the theory, SX-online seems satisfied with a LsC circuit of 6.4mm² and a Shimed circuit of 19.2mm². My solution should offer slightly more flow with LsC at 13mm² (original surface) and with a drilling of 3mm a shimed circuit of 21.2mm². While the extra LsC surface if probably useless and will need to be at least half way closed, having the option is good. Having extra shim circuit surface should allow for more tuning possibility of the HsC via the shimstack with less risk to hit the maximum flow. If this was to happen you could still control it with the poppet valve spacing. If more shim circuit flow is need one could go with SX-Online solution and simply drill some 3.5mm holes in (some of) the blank ridges as I doubt the would be enough room on the ridges to drill bigger than 3mm and remain within the 20mm face shim diameter.
What do you guys think ? Am I out of my mind ? Do that sound solid enough so I should order some shims and take the dremel out ?
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it definitively sounds better than armchair engineering. I will use it again!