shock rebuild using air?
Posted 12 April 2012 - 12:13 PM
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
Posted 12 April 2012 - 12:27 PM
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.
Edited by jayc250x, 12 April 2012 - 12:30 PM.
Posted 12 April 2012 - 01:13 PM
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.
Posted 12 April 2012 - 03:01 PM
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.
Posted 12 April 2012 - 03:59 PM
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.
Posted 12 April 2012 - 06:40 PM
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.
Posted 12 April 2012 - 06:44 PM
Posted 12 April 2012 - 08:30 PM
Posted 13 April 2012 - 02:49 AM
Posted 13 April 2012 - 03:07 AM
Posted 13 April 2012 - 04:45 AM
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.
Posted 13 April 2012 - 05:00 AM
take it for what it is worth
Posted 13 April 2012 - 05:09 AM
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.
Posted 13 April 2012 - 05:51 AM
Most likely dexron 3 seems to be the best candidate.
Posted 13 April 2012 - 06:24 AM
Posted 27 July 2012 - 02:23 PM
Posted 09 September 2012 - 12:14 PM