So I've come to the conclusion that I have to rebuild my shock as the suspension gets softer and me getting lighter most likely nitrogen and oil levels have deteriorated. I weight about 180 to 185 LB in gear, depending on what I drag around with me (Shovel and such) and have measured the following:

On the stand I get 65cm,
Standing on the foot pegs I get 53.5cm (giving me a race sag of 115mm)
standing alone the value of the bike is 62cm (free sag being 30mm)
Preload is set at mid level.

Suspension is stock so the shock spring is 4.7 kg/mm for my 09 YZ250 and according to racetech is fit for a rider weight of 150 lbs or 68 kg.

I measured pressure of the shock and got 100psi so that could be the reason that the suspension is turning softer.

My plan is to change shock oil using hydraulic oil or atf and re-change it once I get some shock oil and refill the bladder with air. As it is quite hot over here the air should be dry   The compressor I aim for brings 140psi which should compensate for higher expanision.

I got myself another shock of a 03 YZ450f  so the spring I have availabe in a month or so will be 5.3kg/mm

Should I use that spring or is it too heavy for me? Or should I loose weight till I reach 150lb (my wife would most likely leave me in the process) Something I'd like to avoid.

I ride strictly enduro, we got some nice service roads, hills and natural whoops, not really high maybe some 30cm.

Question is will I make the current situation better, or worse.

Thanks in advance

Your sag measurements have nothing to do with your shock's action, only the spring.  Your spring is not tensioned set correctly, so we can't tell anything right now.  It's probably not all that far off.  With your race sag at 100mm, your free sag should be 20-25mm.

You screwed up the pressure by measuring it - you can't measure it with a tire gauge.

I suggest you first tighten your shock preload until you have 20-25mm of free sag.  Then, measure race sag.  If it is in the 90-105mm range, it's close enough.  Then re-pressurize your shock - if you want to use shop air, fine, but pressurize to full specified pressure - don't check it, just set the compressor to the specified pressure and fill until air doesn't flow, then yank the chuck off as fast as you can.  Then, ride it.

JayC

Edited by jayc250x, 12 April 2012 - 12:30 PM.

I agree with jayc250x,  you may have lost 50% of your nitrogen charge trying to measure it. It's a really small bladder. Anyway, the spring effect due to the nitrogen is very minor compared to the metal spring as far as setting sag.

Pretty sure the stock spring on that bike is 4.9 kg/mm, and from your measurements it looks like you are pretty close to ok with what you've got it. Increase the preload until you get your race sag to around 105 and then see how much static is left. I'll bet you will see somewhere around 20. If so, that would be good enough to keep the spring you have. To be ideal, you probably need to go up to a 5.1. The 5.3 might work, but you will be on the stiff side meaning you'll have to run with almost no preload (lots of static sag).

You can do the sag adjustment immediately without recharging the shock, but do recharge it for serious riding (Though I have no doubt the remaining 100 PSI will still work fine for the most part). There is differing opinion over whether or not to top it off with compressed air ;-)  You can take it to a local shop for a fill.

Changing the oil is fairly easy if you are mechanically inclined and willing to read about 10 hours of posts and don't mind a little risk. I just did mine in fact. But I would not reccomend it unless you really enjoy this sort of thing. For 80 bucks I could have had a shop do it and be done with it.

Thanks for your help guys, Ok will first try the pre load. The way I looks up the nitrogen charge fast, about half second so I don't think I lost 42psi. I tried it first on a shock I also have to do. That one had 60psi. Sure I lose some but in half of a second it won't be too much.

Over here on the Island there is no way to get a nitrogen but maybe in Caracas. Will put me back about 200 US. I do my bikes and do allmost all work. Now suspension is quite new for me.

The bike has 3 years of riding so I think oil change has to be done. What is better running the bike with an oil 3 years old or a new oil with is not as good like hydraulic oil or ATF but at least they are new.

The spring the RM250 is 5.2kg/mm  at least that is what racetech says. and it is not bad. The problem is that the YZ250 went softer and softer over time so a re build looks as if it is correct to do.

Edited by arnego2, 12 April 2012 - 06:44 PM.

Ok so I now adjusted the preload and have


On the stand now 64.3cm,
Standing on the foot pegs I get 54.4cm (giving me a race sag of 99mm)
standing alone the value of the bike is 62.2 cm (free sag being 21mm)

But still I think I have to change the oil, so I have to change the shock again with air.
I don't think that I should re change the shock as if I have not engough oil the blaller could have a problem.

So your spring seems good for your weight. Regarding the oil question as to whether it would be better to use new wrong fluid or old correct fluid I am not sure.

To partially evaluate your shock I suggest the following. Take the spring off, adjust the compression hi and lo speed and rebound all the way out (minimal damping). Put one end of the shock on a bench and compress the damping rod by hand all the way in. If the shock and oil are in reasonably good shape here is what you should observe.

(1) The rod should be really hard to press all the way in, but possible using both hands and constant force and will probably take a strong guy about 5 seconds.
(2) When you release the rod it should be expelled from the shock on its own at a nice slow and steady rate (maybe around 2 seconds to full extension).
(3) There should be no hesitation at any point and no gurgling sounds indicating low fluid or trapped air. Smooth and silent.
(4) Then try turning the rebound adjuster to the other extreme (all the way in) and repeat. You should now be able to compress the shock but it will stay compressed or move extremely slowly out. At this point slowly turn the rebound clicker out and you should be able to control the rebound speed of the rod in a predictable way.

If it doesn't work like this start looking at the instructions for a fluid change. Some instructions I liked are included in the following thread. The most difficult part is getting all the air out. Good luck.

http://www.thumperta...hange-seems-ok/

thanks, pretty nice Ok  will try it most like anyway when I get the yzf450 shock

One thing you might try is to get an air chuck that has a pressure gauge built in so you can measure pressure while you are applying air so you dont loose as much when you check because the seal is already made.. it wont be exact but it will be close.. also some tire shops use nitrogen for tires so you might be able to build up a cheap nitrogen setup.. look around on the internet there are lots of ways to build a homemade regulator.

I think tire shops over here don't use nitrogen. But I can have a look around at car tuning and ask those guys if they know where to get that stuff. So far I know just in Valencia, about 800 miles west across the water.

Don't worry about using air, as long as its dry air ( filter it from compressor ) it will be omnibus, you cant check the pressure without a no loss chuck,  half a second will be about 1/3 of the volume gone,  they have a tiny volume,  for oil can you get hydraulic oils?  For trucks and jcbs etc? Iso 15 oil for shocks and Iso 22 ( or ideally a mix of 22 and 15 for forks ) if you can get hydraulic oil as them for high viscocity index hydro oil, this is better for the shock where it gets hot,  I would guess most the fork and shock oils you see are 98 % the same as hydraulic oil, in fact ive seen many oils share the exact same specs as common cheap hydro oil,  typically hydro oil is 1/5 the price of fork oil :-)

That's good to know, if the little zosh noise was one third of the volume well that volume has to be really tiny I re tested the other shock I have here to do and that one lost 3psi between tests.

Anyway I can get Mercon V Motorcraft hydraulic oil, but its an ISO46 so Ford says. Or Mercon V Motorcraft hydraulic oil as for the imported ones. Some STP and Honda power automative steering fluids, not sure if they are any good. And the locally produced ATF. Dexron 2 and 3 typed ATFs they don't have much with ISO classification over here. We are kept in the dark.

Fork oils we get mostly W10  it seems that nobody thought of rebuilding a shock so far

Edited by arnego2, 13 April 2012 - 04:51 AM.

I wouldn't use air only because of moisture.The main problem being that if any moisture in the bladder boils when the shock gets hot you will have a very high pressure bladder.When I had my welding equipment I used argon  and I also used dextron atf , with no apparent problems. me being a novice motocrosser  and an old, slow, out of shape trail rider   not sure if I worked anything hard enough to create a problem , let alone knowledgable to notice it.

take it for what it is worth

After reading through the great debate nitrogen vs compressed air I came to the conclusion that I have to a real good rider to note any difference. I think I still have some way to go to get here

The bike has now about 400 hours of running, something like 10 topends I went through and to my shame only when the rear went softer and softer I though of servicing it. I realize now that the better you ride the better your bike has to be, newer tires, fork and shock serviced quite frequently.

Edited by arnego2, 13 April 2012 - 05:09 AM.

46 is way to thick,  ask about for thinner

Will do so, so far I went on to ask if they can give me any value like weight or iso.
Most likely dexron 3 seems to be the best candidate.

http://www.polyperfo...pter-p-286.html

Order one of these!

this is cheaper similar

http://www.ebay.com/...c0b4a8e&vxp=mtr

Edited by farfromhome63, 13 April 2012 - 06:05 AM.

hey that could be the solution thanks, now I need to find nitrogen

You can go to any store that sells compressor equipment and get a filter that will take the moisture out of the air.  Painters use them all the time.

Could someone post a link to nitrogen vs air discussion? I'm searching but can't find it...

How many would you like?

http://www.thumperta...2-shock-charge/

http://www.thumperta...ilshock-oilair/

http://www.thumperta...2-why-nitrigen/