Tuning blackbox speedstack in boxxer wc/team

Udi · 09-24-2006, 04:02 AM

EDIT - Done and done. New pics, page six! (or post #83)

I don't think this has ever been discussed yet, so here it is - has anyone tinkered with the stack yet?

I've had a quick look at the damper, and basically the bottom of the MC damper comes off (and that bottom houses both the LSC port adjuster, and floodgate mechanism). After removal, inside the main MC unit (a little way up) is the shimstack. There appears to be a hex head to perhaps unscrew it but it looked too deep to access with a normal socket wrench.

The reason I ask is because I see somewhat of a need to do it, if you are the type that likes a lighter springrate, more LSC (with a fairly quick blowoff), and little to no HSC.

Running a fair amount of LSC (~5 clicks) with the floodgate (blowoff point) backed all the way off, the fork still wants to spike on high speed braking bumps - which I suspect is very likely to the fact that AFTER the nice easy blowoff, the oil has to pass through the "blackbox speedstack" too. IMO that makes the floodgate adjuster somewhat redundant, as the whole point is so that compression damping can be reduced/elminated after a certain speed threshold.

It wouldn't hurt to can the shimstack all together imo, or at least shim it much more lightly - and i'd like to hear about it if anyone has given it a shot (performance results would be nice too)

Thanks, Udi

KnightChild · 09-24-2006, 05:59 AM

?? The shimstack will be reducing the spike.
The spike may be occuring because you are running too many shims (as you have said) as well as the bypass-valve way too open.
This makes it feel plush at slower stuff (mind you brake dive will be a problem too) but as soon as you hit a square-edged hit at high speed it's forced to go through the shimstack.
My advice is to:
Less 1 (or 2 at max) shims - take the smaller ones off, and close the bypass off as much as possible so that it feels quite stiff (it will brake dive less, and absorb bumps better this way.)

Udi · 09-24-2006, 07:38 AM

You have no understanding of how the motion-control damper works, nor did you do a very good job of reading my original post.

This is nothing like a conventional compression damper where LSC is ported and oil will blow through a surrounding HSC shimstack simultaneously as oil speed increases. The "speedstack" is seperate and oil has to pass through the LSC and blowoff mechanism before it passes through the stack.

I'm not really looking for advice on what to do, i'm wanting to know how to do it. Looking for replies from anyone who has a method on accessing/removing the speedstack which is recessed quite deep.

vitox · 09-24-2006, 10:13 AM

you got any pictures of that?

i was toying around with a boxxer wc and was a bit puzzled by how the adjusters worked and also with how linear it felt in the mid travel, are you also noticing this?

CBJ · 09-24-2006, 10:17 AM

Dosn't Tim Flooks advertise he does shim stack adjustment? I remember talking to a RS tech who mentions something about SID shims could be used but I am not sure at all.

vitox · 09-24-2006, 10:28 AM

Quote:

Originally Posted by CBJ

Dosn't Tim Flooks advertise he does shim stack adjustment? I remember talking to a RS tech who mentions something about SID shims could be used but I am not sure at all.

ooh that could be interesting, maybe not too much for udi as he wants to decrease the damping, but did you happen to hear if it was pure or c3 shims he mentioned (got some c3's i could open)

CBJ · 09-24-2006, 10:41 AM

Don't know.

A.P · 09-24-2006, 11:25 AM

You want your fork without the blackbox speedstack? Get a boxxer race. They are the same fork, motion control, rebound, low speed compression, floodgate......but without the speedstack.

The older races were crappy, but these look to be pretty good. I have a hydracoil team and the internal high speed compression adjuster is such a pain in the ass to adjust, I really wouldnt do it anyway.

teaguers · 09-24-2006, 11:33 AM

The Race does not have the floodgate, or at least it doesn't adjust.

A.P · 09-24-2006, 11:48 AM

RockShox Boxxer Race Suspension Forks feature external rebound and low-speed compression adjustment.

* External rebound and low-speed compression adjustment
* New Motion Control damping with external Floodgate
* 32mm EA70 straight wall aluminum stanchions low-friction coating
* Upper crown allows direct stem mounting (stem not included)
* New aluminum control knobs

...straight from qbp...

davep · 09-24-2006, 05:03 PM

Does your fork still spike if you open the LSC a bit more? I am thinking that maybe the high speed stack is passing the oil just fine, but the LSC (which is not shimmed, and is just a variable orifice) might be causing cavitation and blocking the flow.

In a traditional set up, the LSC and HSC are in parallel. When the oil velocity gets to a certain point, the LSC port is hydraulically locked, but it does not matter, as the oil can (and does) pass through the HSC. Due to the parrallel nature of this set up, the oil can go through either path, un affected by the other path.

If I understand the Mo Co damper, it seems like the LSC and HSC are set up in series. So all oil must go through BOTH dampers. If your LSC orifice is 'to small', it does not matter how much oil the HSC can pass, as they are in the same path. Which ever one has the most restriction, will dictate the maximum flow.

So if you open the LSC gate, and the spiking goes away, then the LSC is at fault. If you open the LSC and the spiking remains, then the HSC stack is not opening enough, and a re-shim is in order.

Sorry i cannot tell you how to get at the stack as i do not own this fork...

post some pics

toodles · 09-24-2006, 05:53 PM

davep - you've hit the nail on the head there I reckon. Is there a way to increase the LSC without starving the HSC circuit though? That would be handy.

davep · 09-24-2006, 06:16 PM

No idea about the shapes and sizes or holes we are talking about, nor the oil velocity, but some orifice shaping might help a little.
I have seen pics of standard shimmed comp heads where someone shaped all of the ports in the head into smooth funnel type shapes. Dont change the opening size, just round off and smooth any corners to decreace the turbulance. This would have not effect at low oil velocities, but at high velocities, the LSC might be able to pass more oil.

peachy · 09-24-2006, 08:22 PM

davep,

what u said is EXACTLY how i understand the MoCo. didn't make too much sense to me that it has a "blow off" (gate) since all the oil basically goes into the LSC first.... then to the HSC. so it seems to me that his spiking may also be from the LSC (5 clicks ...out of 6).

a blow-off (gate) to me is if that opening enlarges or another hole opens up when u hit something hard enough. i'm no expert but it seems to be that having them in series makes no sense.

Udi, how did u remove the bottom piece of the MoCo... just unscrew?

Cave Dweller · 09-24-2006, 09:40 PM

Quote:

Originally Posted by peachy

Udi, how did u remove the bottom piece of the MoCo... just unscrew?

There is an allen screw at the bottom on the side of the MCU stack, about 2 inchs up from the bottom, i think you unscrew that and it comes apart.

Quote:

Originally Posted by peachy

a blow-off (gate) to me is if that opening enlarges or another hole opens up when u hit something hard enough. i'm no expert but it seems to be that having them in series makes no sense.
[/IMG]

It does do that. The black plastic bit is a stiff spring. When you hit something hard enough the other 2 ports are opened that are under the disc show.

Quote:

Originally Posted by toodles

you've hit the nail on the head there I reckon. Is there a way to increase the LSC without starving the HSC circuit though? That would be handy.

You mean trying to increase the platform but still be able to take small and big hits?

The blow off is controlled by the orifice size, but also controlled by the plastic MCU spring which is basically a really,really stiff spring that holds the 2nd,3rd and a bit of the 1st LSC port closed.

To really change things you will need to try and modify the plastic MCU spring i suspect, if you stiffen the plastic spring and open the port a little you will get more oil flowing through the lsc port but the blow off will be higher and will thus provide more pedaling platform effect i suspect. If you soften the MCU spring i suspect the fork would become more plush and wallow, like a marzocchi fork.

I could be way off the mark though