[OreoGitorio]

the rear shock on my ZX is nitrogen charged... but there's still oil in there, right?

I ask cuz some kid on another forum said there was oil on the ground directly under his rear shock (10k miles on it). Some other kid told him it couldn't be from the shock cuz it's nitrogen charged.... that doesn't seem right to me.

[Honclfibr]

Yep, there's still oil in there. Nitrogen is used in place of air in the reserve section of the shock to keep pressure on the hydraulic fluid, ensuring that the cylinder is filled with fluid at all times and acting like an air spring. I believe pure nitrogen is used instead of air because it's inert and doesn't vary in pressure as much with temperature

[gmdboston]

All stock shocks on Kawasaki's (at least the late model stuff) are nitrogen charged shocks. There is oil in the body and res. The nitrogen in the ZX shocks is in the res. separated by either a piston or a rubber bladder. His shaft seal has been cut and the N2 pressure in the bladder has pushed out the oil. Tell him not to ride the bike until it's fixed, and not to think it's fine because it stopped leaking. Once the bladder has fully expanded, it will stop pushing oil out when the bike sits. However, when he rides it, the pumping of thte shock will push out the remaining oil and make the bike dangerous, as well as wear out the shock body. Right now he has a $125-$150 repair. If he keeps riding he will need a whole new shock.

[OreoGitorio]

Cool. Thanks guys, i'll let him know.

[Dichotomous]

you can get ZX shocks on ebay for about $50, so I think speding $150 to fix it sounds a little bit silly to me

[gmdboston]

[quote]Originally posted by Dichotomous
you can get ZX shocks on ebay for about $50, so I think speding $150 to fix it sounds a little bit silly to me [/QUOTE

Yeah, you'd be much better off to spend $50 on a shock, and $15 on shipping for a stolen part that has who knows how many miles on than to rebuild the one you rightfully own.

[Karaya One]

STOLEN??? On the internet????

stop it.

[gmdboston]

Originally posted by Karaya One
STOLEN??? On the internet????

stop it.

No really Dave, it happens......

[Dichotomous]

I'm not preaching ethics or the possibility of buying stolen goods, I'm saying that on a budget it would work.

[gmdboston]

I've seen too much garbage on Ebay to ever think you could actually save money on some thing like this. I've seen frozen adjusters, stripped threads on the body, broken and leaking hoses, rusty shock shafts, wrong parts altogether, you name it. Ebay is ok if you are buying some thing new in a box. I would never advocate buying suspension parts there. Almost all the forks and fork tubes I've seen come from ebay are bent, or smashed. Those rip off artists will say anything to get you to buy their junk and then blame you for the damage. It's not worth rolling the dice.

[Currently]

Even when you do buy new out of the box you can get screwed.

I bought a Penske 8987 for the SV and it took over 8 months to resolve the issues to my satisfaction ... even then ... I just gave up cause I just wanted to ride. They sent me the wrong shock for the wrong bike and it was a friggen mess just to set that straight.

All that grief and misery with endless phonecalls just to save 125 to 150 bucks off of Pete's prices.

I am going straight to GMD for my next suspension needs.

[OreoGitorio]

Originally posted by gmdboston
rusty shock shafts

Pete, is that anything like a Rusty Trombone?

[gmdboston]

Originally posted by OreoGitorio
Pete, is that anything like a Rusty Trombone?

Sort of... It's the reverse modified Greek hold variation.

[hessogood]

If you're feeling frisky get it with the GI Joe kung-fu grip.

[Tabby]

I'm sure Pete at GMD will pipe in here. Isn't the main reason that nitrogen is used , under pressure, is so the oil won't cavitate under extreme use? Under the right conditions, gases held in solution in the oil, can come out of solution and form bubbles. I believe that is a simple definition for cavitation. When this happens enough, damper valving is just moving through what amounts to foam, and doesn't "damp" worth a damn. The pressure on the oil, from the nitrogen, helps keep the gases in solution. If some cavitation does occur, sufficient pressure should force the gases back into solution. I don't believe that the nitrogen is used as a spring. I think that is just a fringe benefit.

[gmdboston]

Next week Hysteresis and it's effect on damping and the recent Patriot failure.....

[Currently]

Originally Posted by Tabby

I'm sure Pete at GMD will pipe in here. Isn't the main reason that nitrogen is used , under pressure, is so the oil won't cavitate under extreme use? Under the right conditions, gases held in solution in the oil, can come out of solution and form bubbles. I believe that is a simple definition for cavitation. When this happens enough, damper valving is just moving through what amounts to foam, and doesn't "damp" worth a damn. The pressure on the oil, from the nitrogen, helps keep the gases in solution. If some cavitation does occur, sufficient pressure should force the gases back into solution. I don't believe that the nitrogen is used as a spring. I think that is just a fringe benefit.

NO! The reason that nitrogen is used is because when you compress oil
in the presence of oxygen, you get KA-BOOM!

That is why you also never oil fittings on a oxygen cylinder or other fuel
cylinders.

[gmdboston]

Originally Posted by Currently

NO! The reason that nitrogen is used is because when you compress oil
in the presence of oxygen, you get KA-BOOM!

That is why you also never oil fittings on a oxygen cylinder or other fuel
cylinders.

Wrong, The reason for keeping the oil under pressure is two fold. One, to reduce the effects of cavitation. Two, to help balance the pressure differential in the different areas of the shock. That's why Head valves and bleed area are so important.

A shock will not explode, under normal use, for several reasons. First the pressures are not high enough to compress the oil to the point of combustion. Second, Hydraulic oil is not very volitile. Third, the is no heat source high enough it ignite teh compressed oil. You can use air to pressurize a shock with out risking explosion, how ever nitrogen is cleaner, dryer, and readily available in high pressure cylinders at very low cost when compared to air compressors that will reach 300 psi. In most performance shocks, the nitrogen (or air) is separated from the oil by either a rubber bladder or a dividing piston.

The welding tanks analogy is incorrect. There is no pure Oxygen source, the pressures are less than 1/10 of the gas cylinders, and there is no ignition source. I have heard from guys that have seen an oxygen/acetylene kit go up. There common thread to the stories is this quote,"it was still climbing when it went out of sight...."

[Tabby]

Hey, thanks Pete. I didn't think about the pressure differentials. Makes perfect sense. Having a balanced pressure would help make the damping more consistent throughout the whole stroke, right? I just like having a good basic understanding of that stuff. Hmmm, ya think that's why you are in your business and I'm not?

[brewmaster]

Another reason to use Nitrogen is that it has a very low solubility and a relatively low coefficient of thermal expansion.

[gmdboston]

Originally Posted by brewmaster

Another reason to use Nitrogen is that it has a very low solubility and a relatively low coefficient of thermal expansion.

Also true. I try to keep it to the Cliffs Notes version on the web. One time we were testing a different piston design for Penske and we had a fade problem. I spent 45 minutes on the phone with one of the engineers discussing what happens to the oil molecules when they pass between the shim stack and the piston lip. I laugh out loud every time some one says they know anything about suspension. Penske has over two dozen engineers, not employees, engineers with Masters and PHD's in Mechanical and Electrical engineering, Fluid Dynamics, Aerodynamics, and a few more in Applied Mathematics and Physics, just to be sure. If you could see the R&D Facilities of both Penske and Ohlins, you would agree that $1200 for a shock is cheap. FYI, Formula 1 car teams budget over a million dollars per year for their shock program. Per car.

[Currently]

Thanks for the clarification Pete.

However, I was taught that a source of heat is not necessary
for ignition if there is enough oxygen, pressure and petroleum.

As for what goes on in a shock, I defer to your knowledge and
experience. I still have a lot to learn regarding that subject.
Don't think I will ever master it but it is the journey ... not the
destination that matters.

[Tabby]

I think my brain only has room for "Cliff notes".

[gmdboston]

Originally Posted by Currently

Thanks for the clarification Pete.

However, I was taught that a source of heat is not necessary
for ignition if there is enough oxygen, pressure and petroleum.

That is true, it's how diesel engines work. How ever with out a heat source you need a lot of pressure to make any oil (diesel fuel is oil, and needs 20-25:1 compression as well as glow plugs to get it going and residual heat to keep it going) ignite. With welding equipment you have 2500 to 3500 psig tanks feeding directly into the gage and pure oxygen. That makes the oil very volitile. Add in heat and sparks from welding/cutting and it's a bad combination. Welding rule number one, never oil your gages.....

[OreoGitorio]

this turned into the coolest thread.... I should get some kind of an award