Just wondering if anyone has bothered to revalve the mid-valve or base-valve on a BOS 888 cartridge, and what their results were, or if they found the cartridge to function better with certain oil types/weights.
BOS cartridge valving? Anyone messed with one?
- Thread starter Kanye West
- Start date
Opened it up, and I think it has the stock stack, but not 100% sure on that.
Midvalve
Compression:
16mm x 8mm x .2, spring loaded
Rebound:
16mm x 6mm x .1
13mm
16mm
14mm
12mm
Base Valve
Compression:
16mm x 6mm x .1mm
16mm
13mm
16mm
14mm
13mm
12mm
11mm
10mm
9mm
Rebound:
16mm x 7mm x .1mm (yes that's a 7mm ID on a 6mm shaft, a real mofo to center up over the ports)
Kind of odd that there's no actual shimstack on the midvalve for compression, but they chose to make a more robust compression stack in the basevalve. I don't see any evidence of wear on the second or third 16mm shims in the basevalve compression stack that would indicate any contact due to the crossover shim either.
Considering the option of making a single stage stack for the basevalve and trying to space out a single stage stack for the midvalve, or even a 2 stage for the midvalve, but probably start simple with single on each with very neutral profiles for a good baseline.
Midvalve
Compression:
16mm x 8mm x .2, spring loaded
Rebound:
16mm x 6mm x .1
13mm
16mm
14mm
12mm
Base Valve
Compression:
16mm x 6mm x .1mm
16mm
13mm
16mm
14mm
13mm
12mm
11mm
10mm
9mm
Rebound:
16mm x 7mm x .1mm (yes that's a 7mm ID on a 6mm shaft, a real mofo to center up over the ports)
Kind of odd that there's no actual shimstack on the midvalve for compression, but they chose to make a more robust compression stack in the basevalve. I don't see any evidence of wear on the second or third 16mm shims in the basevalve compression stack that would indicate any contact due to the crossover shim either.
Considering the option of making a single stage stack for the basevalve and trying to space out a single stage stack for the midvalve, or even a 2 stage for the midvalve, but probably start simple with single on each with very neutral profiles for a good baseline.
Isn't your supposed "compression midvalve" just a spring loaded one-way valve? Damping is likely unintended there. Same case in most forks.
Also, I wouldn't bother revalving anything until you've worked out precisely what issues you have with the stock damper first. You haven't mentioned any.
Also, I wouldn't bother revalving anything until you've worked out precisely what issues you have with the stock damper first. You haven't mentioned any.
Yes, it is.
I should mention that I do not know if those are even the stock stacks, that's just how the cartridge arrived. BOS = French so I'm not anticipating getting a ton of info out of them, but it just strikes me as odd that they'd put a 2-stage stack in the BV. I don't have any issues with the fork yet, but I would just want to start from as neutral a spot as I could, that's all.
I should mention that I do not know if those are even the stock stacks, that's just how the cartridge arrived. BOS = French so I'm not anticipating getting a ton of info out of them, but it just strikes me as odd that they'd put a 2-stage stack in the BV. I don't have any issues with the fork yet, but I would just want to start from as neutral a spot as I could, that's all.
I should state this observation however...
Setting the compression adjuster dead center of it's range I do find myself wanting the fork to stay higher in the travel though. It seems to dive quite a bit under braking. Dialing it in further to cancel out the dive results in some serious harshness on edges.
Ultimately I would like it set up like the custom valving on my KTM forks, which is that it stays generally much higher in the travel and has very linear rebound characteristics while still opening up over edges.
Setting the compression adjuster dead center of it's range I do find myself wanting the fork to stay higher in the travel though. It seems to dive quite a bit under braking. Dialing it in further to cancel out the dive results in some serious harshness on edges.
Ultimately I would like it set up like the custom valving on my KTM forks, which is that it stays generally much higher in the travel and has very linear rebound characteristics while still opening up over edges.
Unless you have some explicit reason to suspect that the valving was changed from stock, it's probably safe to assume that the configuration you see there is stock. Not many people bother messing with stuff like that, and I think the number of people that would re-tune something that is already supposedly "tuned" is even lower.
Anyway, from my experience tuning with shims, if you want more low to mid speed compression (for support) and less high speed compression (to reduce harshness on edges) then you will want more support in the larger shims, and less in the smaller shims.
I'd first get rid of the 13mm between the 16's so you have a conventional pyramid to work with. Then (personally) I'd replace the last 16x0.1 with a 15x0.2, and remove say the 13 and the 12. Someone like Socket can probably elaborate, but in the end it will be guess and check. Hopefully that should give you a rough idea of how things work though.
Before you do all that, I'd work out the weight of the oil in there currently (in cSt) or if you don't know, replace it with an oil you do know the specs of (I use Silkolene Pro RSF 5wt - 26cSt - in everything as a starter). Then ride it again to see if your observations are the same (or not) and tune accordingly.
As for rebound, you'll have to work out what you don't like about it again (i.e. is it fairly linear already, is it too slow from deeper in the stroke, or too slow at the start of the stroke, etc...). Rebound is easy because position relates to speed, i.e. early stroke = LSR, deep stroke = HSR. Personally I thought the rebound damping on those cartridges was well on the slow side (all round), but you mightn't have the same experience.
Anyway, from my experience tuning with shims, if you want more low to mid speed compression (for support) and less high speed compression (to reduce harshness on edges) then you will want more support in the larger shims, and less in the smaller shims.
I'd first get rid of the 13mm between the 16's so you have a conventional pyramid to work with. Then (personally) I'd replace the last 16x0.1 with a 15x0.2, and remove say the 13 and the 12. Someone like Socket can probably elaborate, but in the end it will be guess and check. Hopefully that should give you a rough idea of how things work though.
Before you do all that, I'd work out the weight of the oil in there currently (in cSt) or if you don't know, replace it with an oil you do know the specs of (I use Silkolene Pro RSF 5wt - 26cSt - in everything as a starter). Then ride it again to see if your observations are the same (or not) and tune accordingly.
As for rebound, you'll have to work out what you don't like about it again (i.e. is it fairly linear already, is it too slow from deeper in the stroke, or too slow at the start of the stroke, etc...). Rebound is easy because position relates to speed, i.e. early stroke = LSR, deep stroke = HSR. Personally I thought the rebound damping on those cartridges was well on the slow side (all round), but you mightn't have the same experience.
50/50 chance of it being changed from stock.
I use Maxima 7wt Fork Fluid, which is within 1 cSt of the stock Spectro stuff found in Marzocchis. I wouldn't even begin to look at the stacks unless I already had that squared away as it shifts the whole range.
The rebound feels favorable. Nice and linear.
I was thinking something along the lines of 16 16 15 14 13 11 9, but I'm just pulling #'s out of my ass. Same lines as you're thinking, more face shims for more low speed support and less support towards the inside/top.