NGE

Uhhh...
Sep 6, 2003
197
0
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

~SPONSOR~
Aug 25, 2000
1,407
0
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

Uhhh...
Sep 6, 2003
197
0
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.
 

Robcolo

Member
Jan 28, 2002
342
0
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

Uhhh...
Sep 6, 2003
197
0
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!
 

Robcolo

Member
Jan 28, 2002
342
0
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

~SPONSOR~
Aug 25, 2000
1,407
0
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

Uhhh...
Sep 6, 2003
197
0
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.
 

terry hay

Member
Nov 8, 2003
200
0
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
 

georgieboy

Member
Jan 2, 2001
416
0
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?
 

georgieboy

Member
Jan 2, 2001
416
0
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.
 

marcusgunby

LIFETIME SPONSOR
Jan 9, 2000
6,450
2
It is used a tuning aid, however most tuners only go from a low of 150psi to a high of 175psi, so it wont make the shock much different going from 150 to 175psi.
 

terry hay

Member
Nov 8, 2003
200
0
As a tuner there is a constant need to maintain consistancy to best quantify the value of every change made. Personally I don't agree with the practice of adjusting bladder pressures to affect change. The shimstack works on the oil flow governed by the cross sectional area of the I/D of the shock minus the C/S area of the shaft. The bladder pressure is progressive and is affected only by the oil being displaced by the volume of the shaft entering the body. Remember the only thing that holds your shock intact is pressure. If the pressure in the bladder is insufficient for the shimstack to work against, a low pressure area will develop behind the piston and the sealhead assembly will be drawn into the body. This will affect the shaft alignment and the body or shaft could be damaged. Most Japanese manufacturers recommend appr.150psi. for their mx bikes. High leverage ratio shocks require a greater pressure. Remember - "Things should be as simple as possible, but no simpler".
 

georgieboy

Member
Jan 2, 2001
416
0
Yeah and i was a little low on pressure in the first place, so i really felt the difference. And for the pros, sorry that it sounded a little cruel.
 

Jaybird

Apprentice Goon
LIFETIME SPONSOR
Mar 16, 2001
6,452
0
Charlestown, IN
Oxygen is not a fuel. It is, as JTT stated, an oxidizer...or more specifically, an accelerant. For any sort of combustion to take place, a fuel and ignition source does need to be present. Oxygen will accelerate the combustion process.

Now, simple ambiant temperature or a flame is not all that is needed to produce combustion when the right variable exist. I saw a picture of an oxygen cylinder that was being filled at a welding supply store. Since they also provide breathing air, they used the same oxygen for the welding tanks.
The intake orifaces of these tanks are brass. The worker doing the filling had a tank with buggered up threads, so he decided to place a bit of cutting oil on the threads prior to hooking up the fill connector. It made it easier for the connector to go on, but when the oxygen was pressurized to the tank the friction that was created passing over the oriface lip, coupled with the fuel source that was present (minute amount of thread oil) the explosion that ensued completely peeled the oxygen tank apart like a squished banana. Imagine lighting a cherry bomb inside of a toilet paper roll...that's what it looked like. Luckily the ignorant operator was 50 feet away at the main fill valve.

You can also take a greasy glove, place an oxy/acetalene tourch tip on the glove, pull the oxy lever, and there will be a nice blue flame exiting the other side of the greasy glove.

Fuel (oil), accelerant (oxygen), ignition source (friction) = FIRE!

Compressed air will not do this easily, as explained before it is not pure oxygen.

Compressed air that is not clean and DRY can, and WILL, cause problems when used to charge a shock.
Compressed air that has no moisture content is fine to charge a shock with.
 

MXTex

~SPONSOR~
Feb 29, 2000
417
0
Nitrogen is cheap. The expensive part of getting set up to charge a shock is all the apparatus. Tank, regulator, gauges, hose, etc.. (Just got one on e-bay for $102 :aj: ) I think all this apparatus will basically needed for air or nitrogen. Nitrogen is cheap so why take a chance?
 

NGE

Uhhh...
Sep 6, 2003
197
0
why take a chance?

well, because the bike is an '82 KX125 in very sad shape, and I don't have the setup to recharge nitorgen (although it is cheap, the setup is not)... the shock likely leaks somewhat, so it would be a continuing problem.... and because, with the aid of a $20 mtn bike high pressure shock pump, I can do the changes anywhere anytime...
 

JasonWho

Member
Apr 10, 2002
2,109
0
"How realistic is rebuilding it myself?"

NGE, are you still interested in rebuilding the shock? Have you looked on the www.buykawasaki.com website at the parts diagram and parts numbers? You can look at a place like www.ronayers.com to get an idea on the pricing of some of the parts.

I disassembled a 1983 KX125 shock two years ago. It wasn't that hard. I have disassembled a couple of '87 KDX200 shocks in the last couple of weeks. They are very similar.

If it is leaking oil, then shouldn't you get it repaired, whether you do it yourself or not? Wouldn't adding ANY gas to the reservoir force even more oil out?

Have you looked at a place like Race Tech for spare parts? They have a complete seal head for $38.99.

If it is leaking oil, then it won't be long until your shock is like one of my '87 KDX200 shocks is. The previous owner let oil leak out, then the piston wore through the bushing that is on it, plus wore into the side of the body. The body is shot, the piston is hot, most of the valving shims are rusty, and to top it all off, the shaft chrome was worn away inside the body.

I know you probably don't want to throw money at a beater bike, but if you find a shock on ****, who is to say it won't be in worse shape than yours? Any 1982 shock was made in 1981, so it is 23 years old.

Hope this helps,
JasonWho
 

JasonWho

Member
Apr 10, 2002
2,109
0
I forgot to add:

e-Bay is worth a shot if yours is in real bad shape, though. I got back into dirt bike riding thanks to an e-Bay shock purchase for an '87 KDX200 I had.

Here is one: Item number: 2482231229
 

NGE

Uhhh...
Sep 6, 2003
197
0
wow.... thanks for going the extra mile.... sorry to say, but the bike blew it's lower connecting rod bearing on the very next ride after that post... lol... I was going to mention that in my last post but forgot.... anyways, at this point I have a '82 KX125 parts bike around.... need any parts?.... I'll give ya a freebie part (you pay shipping) for the help though!!
 

JasonWho

Member
Apr 10, 2002
2,109
0
CONCRETE THING THAT HOLDS BACK WATER!!! Sorry to hear that about the bike. You are welcome on me trying to help. I couldn't use any of the parts. You should try to part it out on e-Bay. Someone else might be able to use the parts to keep their bike up and going.

Good luck and again, sorry to hear about the bearing
 


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