shewie

Okay, thanks Banshee. I wonder if the stock valve could be drilled to mimic the Gold valve. I think I need to do a lot more research on this. First thing should be to find a local suspension expert who can explain the shimming to me.

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Where are we going and what am I doing in this handbasket?!

Banshee

What happens, is that there is a hole through the valve that is sealed off by the shim stack. This is a sort of conical stack of thin shims. When you hit a bump, the oil tries to flow through the hole, but the shims are closing it off. So the oil has to bend the shims out of the way to get past. The exact number, thickness and diameter of the shims used in the stack set how much it can be flexed initially and how far it will flex with continuous pressure, ie fast & slow damping response.

I would guess that a 'flatter' cone of shims would let it have softer damping & a steeper one would give harder damping as it would take more pressure to produce the same deflection in the shims.

I can see what I am trying to say in my head, putting it into words is not easy, however.

While you could drill the stock valve, I don't think it would be practical, as you would need to find the right shim stack by trial & error. Very costly in time & dis/assembly, I would think.

shewie

Hmm. I think I understand what you're saying. I would have to have it in front of me to really get it. You say the stack is conical? So the shims are of progressivley smaller diameter as they get nearer the rod? I'm off to try to find some shock diagrams and see if I can get on the same page as you.

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Where are we going and what am I doing in this handbasket?!

Banshee

That's right. Widest at the valve, getting progressively smaller in diameter as they are stacked. There may be several the same size, depending on the response you want from them. In the pic of the valve, the shims are those discs held on by the zip tie through the middle of the valve. Not a good picture of them, though, I was aiming to show the holes in the valve there.

If you look carefully, you can see some of the smaller ones from the bottom stack half hidden by the valve & top shims. The ones on the top are rebound shims for the 4 small rebound holes.

smurf211

Banshee, John was saying something about converting the stock shock to oil over oil vs gas over oil. We were long distance and he was involved with something so we didn't have time to pursue. I guess I can call him back and discuss that issue solely. Have any idea where he was going with this?

Great write up, the further we progress here the better. When I get the 900 shock in I'll take some shots of it next to another BB shock I have.My original plan was to send the second shock t0 John and have him rework / re-spring it. This was last winter. He told me not to worry about it until I hit the 15- 20k mark. He did advise that the setting should be 1/4 inch of thread showing and a half turn back from max on the rebound.

Banshee

Not sure exactly what he means by oil over oil, but I do know about the gas over oil.

Working from memory, so some details may be a little off.

Basically, inside the shock, you have the oil that acts as the damping medium. In the OEM BB there is no reservoir, so you have a fixed volume. Until you compress the shock, that is. Once you compress it, the shaft is also inside so you have less volume for the oil. So you need to have gas in there for compressibility. Then you have the issue, that you need to keep the gas & oil separate to prevent bubbles messing with your viscosity.

So at the top of the shock is a sealed chamber, (in the 900rr shock, this is in the remote res), that contains the pressurised gas. The end of this can move. During assembly, the movable cap is pushed in, oil filled in the main chamber then the valve goes in on the shaft. Oil topped up & the sealing caps go on so there is no air or gas in the chamber with the valve. Then the shock is turned over & the top chamber filled with pressurised nitrogen.

This is a fairly high pressure as the gas will act as an additional spring in effect. If for example the shock caused a 10psi increase in pressure & the chamber was at 10psi to start with, that would be a 100% increase in pressure giving a substantial change in the 'spring rate' of the gas. BUT, if the same chamber had 100psi to start with, it would stil only have a 10psi increase to 110psi, so now it is only a 10% increase in 'spring rate'.

In the 900rr shock, the oil fills the body of the shock & the line to the res. There is a one way valve on the res to adjust a secondary oil path for more or less compression damping. This valve is bypassed on the rebound route. There is another valve to adjust flow on the rebound route. On the OEM BB shock, there is only the rebound adjuster. It is effectively an extra hole through the valve which alows oil flow on the rebound stroke. The adjustment screw allows you to vary the aperture of the 'hole' by screwing a pin in/out.

So says the guy who knows enough to understand what the experts are talking about, and what NOT to touch!

smurf211

So the difference between the front and the rear is pressurization due to increased weight and workload? Nitrogen for heat and gas stability. Not adjustable in terms of gas but adjustable in terms of fluid flow, although some are. Another thing, how do the techs know how to stack the shims and in what order? I understand the conical concept, I guess there is a basic design and the shims are added , subtracted, stacked according to weight and desired damping. Just looking to gain a better understanding, this level of detail is new to me.

I took a look at Traxxion dynamics. Although expensive, I realized one of their key selling points in the ability to remove their cartridges and re-install the old components if you sell your bike. This will allow you to move the cartridges to a new compatible system, probably with a little fine tuning (read as repeat business). Essentially they are providing a cartridge insert that has the springs, comp and reb setup up per your spec with pre load adjusters as an add on. Last time I checked they were about $1100. (with out the preload option). fwiw, -sm

Banshee

I believe the use of nitrogen is simply that it is cheap & dry. After all air is 70% nitrogen.

As to how the tech knows, Racetech supply a list of stack specs for each bike & rider weights. If you need a change after that (for fine tuning on track etc), then the tech need to know how to adjust it.

smurf211

I posted this in the wrong thread. Here's the link, sorry for the rant.....

Suspension for dummies:

BackStreet

I just put a progressive spring on mine and the stock shock is fine IMO.

If some other available shock is too short why not just make a longer bracket for the top mount?

smurf211

You've just illustrated another solution. It's about endless. Good call.

Banshee

For me the stock spring was fine, but I found the valving too harsh. Replacing the OEM valve on the BB shock on my '98 with a Gold valve made a fantastic difference.

lois

Scott.....maybe the best way to go in the long run might be with an adjustable unit....no offence to anyone, but doing up the stock unit sounds like you won't have many adj options .


Lois

__________________
Call me "Captain Mudbucket".

shewie

I agree, but I am going to try to adjust my stock one and see if I can live with it. I'm not sure where the damping is set and if it has some more available it may be enough for me. If not, I guess the RR shock is the next step. I have to talk to smurf some more an dsee what else he's discovered.

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Where are we going and what am I doing in this handbasket?!

lois

Ok then....so what does this mean...


>
There is something brewing on this topic. Stay tuned for another of smurf211's excellent write-ups. BTW, you may want to hold off on that, Lou, unless your Gixxer is boring you and you want to take your bird to the track. <





Lois

__________________
Call me "Captain Mudbucket".

Banshee

Shewie, the only adjustments on the OEM shock are rebound damping adjust by a screw that you can see on the bottom of the left side where it is bolted into the triangle plates. And spring preload, by the 2 BMF locknuts on the top of the spring.

On my '98, I was quite happy with the OEM rebuilt with Gold valves, but in hindsight, I would have preferred more adjustability for when I my wife was pillioning. If you don't do track days, carry passengers & use the bike for the same type of riding all the time, (ie either weekend fun or commuting but not much of both), you could get away with the set & forget of the OEM overhauled.

If you want to be able to set it tot suit those times when you DO have a pillion, or go for a more spirited ride or hit the track, then a more adjustable unit will be better. That is where it gets harder to decide, do you go for a 900rr & rebuild it, or go whole hog & get the full aftermarket shock. By the time I totaled up all the costs & steps involved, my rebuilt 900rr probably cost me nearly as much as the cheapest possible aftermarket I could have bought from over there & had shipped out here, but that would have lacked the remote res. So over all I think I made the right choice. It also meant the spend was over a longer period, so cushioned the cost.

It's a real "What type of riding do you do & what do you want it to do?" sort of question.

smurf211

Got the 900RR shock in today and took some stills next to the stock XX. I'll be discussing the options for both when I take her in for the front end. The RT springs showed up today as well. When I get the pricing for the rebuilds I will pass it along. One note John suggested that preload be adjusted for 1/4 in. showing on the threads. I took a picture of mine mounted on the bike. The other was the rebound, which is fully clockwise and then backed off a 1/3 of a turn. I should have an update in a couple of days.

That tube is spacer material that can be cut to length as required. The preload on the stock XX shock is not set per recommendation. Compare to the one on the bike.


The CBR900rr wet weight is 460 lbs. if your looking at the spring difference.

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CiscoKid

Look at a Hagon do a search there is a recent post on it

shewie

Smurf is currently noodling on what he is going to do with his. I'm sure you have noticed from his previous posts that he is quite thorough (and extremely anal, but don't tell him I said that) and will examine all the angles before he decides, including talking to Jaws, who is apparently an even greater Blackbird authority than is generally acknowledged around here.

Once his research is done I'm sure he'll let us know what he has decided on. Then he will post an excellent write-up which will include pics and source info (are you reading this, Steve?) so the rest of us can reap the rewards of all his hard work.

So you may want to hold off until you can take advantage of this research. Understand?

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Where are we going and what am I doing in this handbasket?!

smurf211

Too much for my own good sometimes. I will be talking / taking my bike in to the suspension guru on Tuesday in prep for the front forks. The team is taking the weekend off after a grueling week of Laguna Seca prep. I’ll be dropping off the front end parts and the two shocks and find out when he wants the bike. Plan on leaving it and we’ll dial it in when I pick it up.

I have had a chance to gather all of the information up on the Comp and Rebound GVs, the springs, etc and logged in and printed out the settings for the valves and actually had time to put it all together and read it. I was going to scan these and post them up but I've got a strange feeling about copy right stuff so I am just going to cliff note it and post it up.

Here's an interesting note: The work sheet for my rear shock actually calls for a slightly less rate than the stock. I also looked through some documentation from last November and the stock shock can be good to 250 lbs, depending on preload. Also, there is the following additional work that needs to be done.

Bleed hole: 1.0 mm #60, drill piston if required.
Tap body for 5x0.8 for Nitrogen valve (Schrader) SPNV 0512 for 285 PSI.
Recommended spring rate 16.5 kg/mm vs 16.8 kg/mm stock <<<<<<<<<
Adapter collar for spring
Shock preload 12 mm, rear end sag 32 mm
Rebound adjuster 1.5 turns out
Of course this is after all the mods.


The key to all of this is the Access Code on the GV doc you receive when your GV package arrives. After you enter in your settings and requirements it calculates a general setting level that you can ride on and should be pretty close. It will be up to the more discerning riders what tweaks they want to make.

I’ve got 11 pages of this and will go through and condense everything and put it on the fork post. The docs explain the shims, bleed holes, building the valves, torque, Loctite, etcetera.

I went out again this morning. Great time to mull all of this over. The playlist is finally dialed in, the GPS is showing what curves are coming up, a feature I hadn’t thought about, haven’t gotten a ticket yet, and I laughed thinking after I beat this to death I’ll probably end up with a Penske on the back like everyone else. More later….