Nitrogen shock questions

NGE

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#1
can you run air in a Nitrogen shock?(it's got a schrader valve)

I read the thread about the bladder burst (looking for an answer to a different question) but no one comments on the fact that he put air in it. (made the same mistake... but I don't think it has caused any harm yet. I doubt that I got any air in it... but I tried)

Does the typical motorcycle shop have facilities to fill it with nitrogen? cost?

Would the bikes rear sag considerably, even under just it's own weight, if the nitro was really low?

Is it possible that it just lost pressure over several years of just sitting, or is it, most likely, leaky?

How realistic is rebuilding it myself? (I am mechanically adept and have worked on other shocks and forks.. Mtn Bike... hurt myself pretty good with an air shock that had pressure in the negative pressure chamber)

What are the cautions to working on a shock yourself?

Are shocks for old bikes readily available? where?

Is a rebuild something you want to send off, or can a local shop do an adequate job?(not a racer)

Thanks for your input.
 

JTT

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#2
Whow...lot of questions there ;)

First, regarding the air/nitrogen thing, there was a real good thread a short while back that went into this very well, suggest you do a search.

Most (or at least many) shops do have nitrogen, particularly larger or specialty shops.

The nitro will have "some" effect on sag, but big effects on shock operation.

Yes, it can leak out over time. Bladders also become worn and damaged with time and use.

It's really not too hard to work on them, but suggest you have someone experienced "show you the ropes" first time through. The biggest hazard is making sure the nitrogen charge is completely out, and that everything is fully secured and right before recharging....we're talking substantial pressures here (170-190psi) that can be dangerous. :scream:

Rebuilds are generally best handled by an expert, or at least someone with experience. Simply changing oil is only doing half the job, and that's what you get with some "local shops". :think:
 

NGE

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#3
Originally posted by JTT
regarding the air/nitrogen thing, there was a real good thread a short while back that went into this very well, suggest you do a search.
I did do a search before posting this... can you give me a link to that convo?

Thank you for the input... I live in St Paul MN, so Bob's Cycle supply is only a mile away... they should be able to charge my shock then it would seem.
 
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#5
NGE------Eeric Gorr offers a video showing complete teardown & rebuild of shocks & forks and it's very worthwhile. Race Tech has separate videos for shocks & forks & their rebuilding and installation of their Gold Valves. Unfort, you have to buy the GVs to get it. There are many opinions on using pure Nitrogen [N2] vs air [79 % N2]. IMO [BS Chem & Physics] there is no PRACTICAL advantage using N2[theoretical advantage, maybe]. In older shocks where the gas contacted the damping fluid, there was oxidation of that fluid and resultant degradation and loss of gas pressure. This is not the case in a bladder fitted shock - the gas is contained in an imperveous neoprene bladder which could care less if it contains air [79% N2] or 100% N2. Air and N2 expand & contract virtually the same during temperature fluctuations due to physics gas laws. The only problem with air is moisture. Air can hold up to 4 % moisture and water changing phases from gas to liquid may make a small difference in internal pressure. Fortunately, compressing air removes a large part of its moisture burden. Varying internal pressure in the shock a few percent makes little difference in the shocks response. The crossection of the shock rod is around 1/4 in. sq. so a change of even 10% internall pressure would amount to around 5psi against the spring. The pressure is in there mainly to prevent cavitation foaming and to keep the shaft seal tight.
 

NGE

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#6
Thank you for the insightfull reply... you should read the thread that JTT suggests it is very informative.

After reviewing what was said here and in that thread, along with input from an aircraft engineer and some common sense, I came to the same conclusion you did.

Check that thread and throw in your 2 cents!
 
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#7
i am using air in my shock. For over a half a year now. No problems whatsoever. I can tune it myself. Great.
 
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#8
That whole thread that JTT is refering to started off on the wrong foot with JBird mentioning Oxygen where he should have typed AIR. Actually Oxygen would work, but why invite trouble. If the reservoir got too hot an autoignition could occur. I've used air in my shocks [and forks] for years. Now, do the Nitrogen Nuts out there use N2 in their forks? Here, the gas actually contacts and mixes with the fork fluid & is in contact with your internal parts 100% of the time --24/7.
 

JTT

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#10
Originally posted by Robcolo
If the reservoir got too hot an autoignition could occur.
I'm no chemist, but I always thought that oxygen was an "oxidizer"? (intensifies reaction, but isn't flammable itself) It would still need a fuel to burn wouldn't it?
 

NGE

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#11
Originally posted by JTT
I always thought that oxygen was an "oxidizer"? (intensifies reaction, but isn't flammable itself) It would still need a fuel to burn wouldn't it?
Oxygen is a fuel... it will not burn without another fuel source and approriate temperatures... which are very high in this case.... theoreticaly the aluminum in the shock body could be a fuel, but the temps would have to be extreme... (your seals would have blown out long before the temp was high enough to light aluminum aflame... thus relieving any controversy about air getting in there.... same goes for your oil)

I switched to air in my shock and I can now adjust my spring in 10 seconds ANYWHERE I want, because I have a tiny hand-held high pressure air pump.

Having looked into this extensively and reading all that is said here about it, I can see NO advantage to N2.... the expansion rate under heat is nearly identical to air (which is mostly Nitrogen anyways)... the corrosion issue is moot... the explosion theory is ridiculous (unless you ride your bike in lava streams).... air is easier, cheaper, and more adjustable.
 
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#12
NGE
Your'e right. However as manufacturers are ultimately liable for their products they have to be seen as covering all the bases. A few facts should be cleared up here though. The biggest danger comes from two areas. This is only the theory behind the thought process and in our case has little "real world" value. Number one; The possible moisture content of the air boiling in the oil creating a rapid expansion of the fluid behaving in a violent manner. Number two; The possibility of what is called a seat explosion. Most materials have a natural affinity with oxygen and seek to combine at a molecular level. This can often result in a disassociation of chemical or molecular bonds in the original material in order to accept the oxygen molecule. Oil and in particular grease when in the correct ratio with oxygen can be extremely hazardous. A rapid oxidation of the material can occur and result in an explosion. This requires no ignition source and no excessive temperature. Given the quantity of oil to oxygen in our case the mixture will always be too rich for it to explode. Also the bladder or piston seperating the oil from the gas negates the possibility of both scenarios. Bear in mid the fact that it is only pressure that stops the seal head assembly from moving and maintaining correct alignment. Go too low and you could pay dearly.
Regards
Terry
 
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#13
Just yesterday i checked my air pressure in the shock. I used about 125psi for a year now as i found it worked nicely. But yesterday i decided to go for the old 175psi and got a completly different shock. Much firmer on comp and quicker on rebound. How nice without changing shims.
Is it possible that suspension rebuilders only change pressure to obtain what the client want?
 
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#15
Well, also a legitimate one can do it within the book.
Since you asked for a firmer shock, that is what you get!
I mean: you didn't asked for a revalve, did you? Only firmer shock.
Just an other way of tuning the shock.