Pitpro 160SE, rear shock help please.

[djeuro1981]

I just took a bike for a test ride for a mate as he is looking at getting into the pit bike scene also and it was a pit pro 160 SE model, i sat on it and the rear suspension felt like i was jumping on a trampoline, does that mean the rear shock is buggered??

 

[my67xr]

it possibly means that the seals are leaking in the shock, and might have lost it pressure.
you might be able to get the Nitrogen topped up at a tyre shop if it has a Shcrader (car type) valve fitted to it.
it should cost under $20 to top it up.
then see how the shock responds.

otherwise a new shock isn't that dear, measure the old one eye to eye, (mounting bolts) and have a look on ebay for a replacement,
the DNM ones are good for the money from what i've heard

 

[djeuro1981]

awesome thank u so much for the quick response

 

[Blender]

Is your bike running 17/14 wheels? Iirc the shock is a bit of an odd size, (305mm Isn't it ?) and alot of after market manufacturers don't make shocks in that length.

 

[stoozo]

Cheap china shock? If the seals are gone I wouldnt bother paying $20 on getting a nitrogen re-fill it. Just do it with a compressor....oxygen is mostly nitrogen, people worry about a tiny bit of moisture but dont worry about it, maybe if it was an elka or something good, then Id bother going to get it filled with nitrogen.

If its on its way out dont waste your money!! Just find someone with a compressor that will do 180PSI-200PSI pretty sure that is the common PSI level for a shock. Most tyre shops will max out at 180PSI as well. I remember some bicycle shops have 'shock pumps' that work too. I used to have a 'air shock' on my MTB years and years ago, used to have to get it pumped up every few months at the bike shop.

Im going to do one in the next couple of days with a compressor if you're worried about doing it like that!!

 

[my67xr]

the nitrogen helps the shock to not overheat too, have you felt the heat in your shock after a decent ride ?
air doesn't help the cooling, all the seals cook and go brittle causing premature failure

 

[stoozo]

So 22% is going to cause that much of a problem??? Really....

The common name given to the atmospheric gases used in breathing and photosynthesis is air. By volume, dry air contains 78.09% nitrogen, 20.95% oxygen,[1] 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases.

Give me a bit Im sure I know someone on facebook who is a chemical engineer...

Atmosphere of Earth - Wikipedia, the free encyclopedia

 

[Chops]

The best 4wd shocks for corrugated roads are? .................. Drum roll .......... Nitrogen filled!:thumbup:
And the closest replicated environment to that is dirt riding on bikes.

 

[my67xr]

think you need to do a bit more research stu.

taken from Wikepedia here-
Many shock absorbers are pressurized with compressed nitrogen, to reduce the tendency for the oil to cavitate under heavy use. This causes foaming which temporarily reduces the damping ability of the unit. In very heavy duty units used for racing or off-road use, there may even be a secondary cylinder connected to the shock absorber to act as a reservoir for the oil and pressurized gas.

a quote from another dirtbike forum-
Take it to a shop, DO NOT USE AIR. I've seen a shock reservior blow apart out in the desert. The guy said he pumped it up with a big hand tire pump and when it got hot, it literally blew the side out of the reservior, right into the guys leg. They called the ambulance and he went away in the ambulance. Everyone who saw it was shocked, wow, none of us have ever seen that before. Dude, don't use air, have a professional fill it.

another motorcycle forum, from a shock repair company-
Some dampers are charged with gas, typically nitrogen. These shocks have an extra unattached piston in the bottom of the damper cylinder, with oil above the piston and high pressure gas below the piston. When you hit very large bumps at high speeds, causing very high damper piston speeds, the floating piston will move, reducing the damping and allowing the shock to respond faster. Also, on an emulsion shock, if the damper piston moves too fast it can pull so hard on the oil that bubbles form. This is called cavitation. These bubbles form in thousandths of a second, but can take hours to pop. As long as there are bubbles in the oil, your dampers are pulling through a mixture of oil and foam. This ruins your damping. The free floating piston will keep the oil pressure above the cavitation pressure. Typically, nitrogen at 30 to 300 psi is used because the oil won't combine (burn) with the nitrogen nearly as easily as it will with the oxygen in normal air.

 

[stoozo]

Lol Yeah cause everything you read on forums is gospel....I was making the point the **** that comes out of everyone's compressor is 79.02% inert gas in the form of nitrogen and argon the other parts are oxygen and carbon dioxide...the remaining 5th...so that remaining 5th the 20 odd percent is 'bad' for your shock....as I said ill talk to my chemical engineer mate. He will actually know why or why not that remaining 'bad' non nitrogen part the 20% of what comes out of your compressor that will completely mess up the works....the misconception here is 100% of the air of breath is made up of oxygen. When its actually almost 78% nitrogen and only 21% oxygen with 1% argon...this is a matter of chemistry not 4wd forums answers ;-)

Sent from my WT19i using Tapatalk

 

[Chops]

Ok I'll never buy a brand name shock ever again coz those guys just don't know what they're doing. I feel jipped now I know it's just compressor air needed.

 

[my67xr]

did you see what i posted up above above?


so if you can just use air, why wouldn't the china shock manufacturers be using it instead of nitrogen ?

and you are right, you shouldn't believe everything you read on forums,
just look at what you have been saying about nitrogen/oxygen.....




it says that air cavitates and mixes with the oil in a millisecond
these bubbles make the area of oil larger, and end up forcing the oil out past the seals, killing the shock prematurely.
the air also expands with heat, nitrogen is way more stable
a rear shock can get up around 200° the rubber o'rings can't hold up too long at those temps.

 

[Cordogs]

Looks like I need to start reviving some old threads! Cause this topic was dismissed in detail about a year ago with pretty much that exact same answer!



Reps to Craig for putting this one to bed, Again.....

 

[stoozo]

Ok ill start thinking that the air I breath is 100 oxygen!! Easy....shove head up arse and ignore the most basic chemistry on the planet....hahaha and you think China uses nitrogen in their shocks....lololol yes 79% nitrogen...etc

Sent from my WT19i using Tapatalk

 

[stoozo]

Looks like I need to start reviving some old threads! Cause this topic was dismissed in detail about a year ago with pretty much that exact same answer!



Reps to Craig for putting this one to bed, Again.....

What ignoring chemistry happens on here all the time? Oh dear....


Sent from my WT19i using Tapatalk

 

[my67xr]

so are you saying all the shock manufacturers are just pulling the wool over our eyes ?
Showa, Fox, Kayaba, Bilstein, YSS, Ohlins, Fastace, DNM etc etc are just using air ?

 

[Cordogs]

What ignoring chemistry happens on here all the time? Oh dear....


Sent from my WT19i using Tapatalk

I didn't realise you were a Chemestry Proffesor? Or a suspension engineer!

The answer you have been givin is the same answer that was giving last year to the person who asked it, why you may ask? That's easy, because it's the right answer! Ring around ask the suspension experts! Craig has a "Spanner Spinner" title because of his years of experience with mechanics. If you don't like/agree with the general consensus go right ahead consult the experts in their respective fields!

Your belligerent behaviour will not be tolerated!

 

[stoozo]

Oh wow ban away then if I'm being belligerent....I said ill consult my mate who is a chemical engineer mate I went to school with....lives in Singapore and works for fosters, he did a double degree chemical engineering and economics. He will know! I also said ill do my shock with 79% nitrogen and see what happens all well knowing its not going to blow up unless I'm a red neck who pumps it up so hard it'll actually heat up and turn into a bomb! I think the fact you're threatening me as a mod when I'm simply asking a question that is yet to be answered is well ****ing immature corpdog

Sent from my WT19i using Tapatalk

 

[my67xr]

no it might not blow up, but people have had it happen when out riding.
pressure builds up until something lets go.


but if you are adding compressed air to a nitrogen /oil filled shock, this is going to cause more problems than just pressure/explosions etc.
with any percentage of air/oxygen in the oil over 2%, it can allow the oil to cavitate and cause hundreds of air bubbles in the oil, only takes a couple of seconds if that to happen.
then the air bubbles can take a day or so to diperse.
the air bubbles don't flow as easy as the oil through all the valveing inside the shock,
and this can cause heat, and cook the seals/o'rings, and the extra pressure needed to force the aerated oil though the valves will make it blow out the seals resulting in a dead shock.


if you were to ask a suspension specialist he will tell you the same thing,
when they top up a shock, they create a vacuum first to suck out any air inside.
most places wont top them up as they will tell you it has lost it's gas pressure due to leaking seals.
and advise you to have your shock absorber rebuilt

having it topped up at a Tyre shop, they will just do it as that's what you've asked.
and doing this you will find out if the shock is still good, or weather it is leaking for a minimal cost.
it could save you throwing money away if a top up fixes the rear shock.



another thing,
you shouldn't tell people it is ok to top them up with air, unless it's a specific air filled shock.
if they do it and their seals blow out due to you saying it's ok to do, then they aren't going to be too happy with you either.

 

[Cordogs]

Happy too, I don't like the cut of your jib!