Vintage Dirt Bike Q & A

Im rebuilding the rear shocks on my 1980 cr250. Does anyone know how muck oil and how mush nitrongen goes in them?

Where did you find new seals?

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One is not enough.

I havent found seal yet for the shocks, infact, I havent even took them apart yet, im just trying to get all my information up first. But if you find some seal, let me know where you found them. So if any one know how much oil and nitrogen goes in them, please let me know.

are your shocks the reservoir style. i got seals for my 80 cr 125 shocks with the ressys from vintage elsinores. he was in the process of moving when i got mine. the web site will not work nor his phone anybody know how to get ahold of him thanks jay

These are gas charged shocks with reservoirs right? Those reservoirs have either an air bladder or a floating piston, right? If those answers are both yes, then you will be hard pressed to find a specific oil volume spec.
Try this:
Get it all clean
Clamp the top eyelet in the vise so that the open reservoir and open shock body are sitting up like two cups ready to be filled.
Fill the reservoir about 1/3 of the way full and pour a bit of oil in the main shock body.
Push the bladder into the reservoir just far enough to allow the retaining ring to go in.
This process will spill oil all over the place, so catch what you can with a catch pan.
Pulling that bladder up carefully into place now is the safest way to seat it.
Fill the main shock body almost to the top with oil.
Fit the piston into the body, rocking it a bit to allow air bubbles to escape.
Press the seal head just far enough in to fit the retaining ring in the groove.
Is that oil catch pan still in place?
The safest way to seat that seal head against the retaining ring is by pulling it up now.
To absolutely minimize the amount of air in the shock oil, you might consider adding a very small amount of pressue to the schrader valve to seat the bladder and seal head with internal pressure. This is dangerous though because an improperly seated retaining ring will cause projectiles and an oil gusher in your face if the pressure pushes everything out. And, you don't want to over stretch the bladder by pressuring the seal head and the bladder too far out to seat them. I start with a bit of a dimple in the bladder to allow more expansion without over stretching it.
Either way, if you survive, add a small amount of air pressure to leak test. Leave air in the shock until you get it to a Nitrogen bottle. Then let the air pressure out and refill it with Nitrogen.
Nitrogen pressure of 150psi will put you in the ballpark.
If you are ever in a bind for shock seals, your local hydraulic shop will be able to get them - almost always.
Enjoy!
Jon

Thanks jon, that was a lot of help. I guess I will go ahead and take them apart. What wheight shock oil do you reconmend?

It seems like Bel Ray HVI 5wt is always the right spec for stuff of that era. If you aren't too committed to always using exactly the product according to the label, or if you just finighed reading "Zen and the Art of Motorcycle Maintenance", then you might want to try ATF instead. It's very good quality hydraulic fluid, good enough for a $5,000 car transmission, and very well designed for use in shocks and forks. If the viscosity feels good in the application then you are set. As an in-the-garage ball-park check: look for quick compression movement and noticably slower rebound movement. If the shocks sound all squishy when you move them in and out, that just means you didn't get all the air out of the oil. Taking them apart and trying it again is much cheaper if you use ATF as a starting point.
Enjoy, Jon