Hi all. I just reciently picked up a 85 Honda ATC250R. The bike is stock except for a pipe and K&N.

I want to rebuild front and rear shocks. I would take them in but I am straped cash.

Where can I find instructions?

 

a honda service manual is the best. you can get a clymer too. rebuilding the forks isn't too hard, but the shock is a little more involved. if the shock still has some compression damping when you push down on it, and rebound damping when it comes up, then you might want to leave it alone if you want to be cheap. if you want to change the oil and recharge, its not too big a deal. you just need a no loss pressure gauge and a tank of nitrogen. but replacing the bushings and seal pack are another story and more $. the forks are easier to do bushings and seals.

 

How much nitrogen pressure to fill to after the rebuild on the front? How much pressure in the back to "top-off"?

 

you don't pressurize the forks with anything. infact, after each ride, technically you're supposed to raise the front wheel off the ground and depress the schraeder valve on the fork caps to let out the built up air pressure for best performance.

as far as the rear shock goes, the service manual says 185-230psi for 85 models, and 284-327psi for 86 models. so you won't be checking this with just a tire pressure gauge or something. to properly check it you need a no loss pressure gauge which are about $140 from motion pro. maybe a dealer would have this. but just "topping it off" might not do anything. because the reservoir bladder could be torn, the line fitting could leak, etc. the point is you're not going to know unless the shock is rebuilt. the oil is probably original, and should be changed for best performance. but if you're not going to be riding it hard, then you probably wouldn't notice the new oil's benefits.

if the shock still has compression and rebound damping when you push down on it, and you don't want to spend much $, then you should probably just leave it alone.

 

Read somewhere that the front was pressurized to something like 6 psi. In hydraulic systems there is no air at all thus the hydraulic fluid will not foam and it will be stable. In a shock there is a combination of a hydraulic and pneumatic system. If the air side of the system is not pressurized to some value the fluid will foam because the density of the fluid is greater that the density of uncompressed air. I do not understand how you would build pressure in the shock (or fork) while riding. If the fork is sealed no additional air could enter or exit the fork while riding. If there was a smal leak the pressure in the fork would decrease By no mean I am I saying you are wrong on what honda says to do....

The reason I am asking is that I do not have the service manual.

Maybe we are saying the same thing but differently. With no weight on the front end the fork would fully extend do to the spring inside (there is a spring inside correct? If not the weight of the front tire and break + gravity would cause the fork to extend). The spring would put a positive downward force on the fork thus causing a vacuum condition inside the fork. When the valve is opened it would then balance the pressure inside and outside. As soon as you set the bike back on the ground the fork would start to compress thus causing a positive pressure inside the fork (this is the pressure I was looking for). I can see this more of an issue when you take a bike from sea level to the top of the rocky mountains. The pressure inside changes as you change altitude (this pressure change would be small becuase of the fact that the fork is a ridid vessle unleike a tire). You ever forget to take the pressure out of a bike tire while going up a mountain? I made this mistake on my kids bike 2 months ago. Before going camping I checked the tire pressure and filled it up to 5 psi below the max rating. Then went up to about 4000 feet, pulled the bike off the bike rack and both tires had exploded.

Again I do not have a manual so this is why I ask. If the manual say to lift the fork and open the valve that is what I will do.

As for the back. I do have a non-bleed pressure gauge and a cylinder of nitrogen. I fully under stand that if I check the pressure and it is say 100 psi. I should go ahead and fill it to the # you gave me. If I go for a ride and then check again and in say a week or so later and it is back to 100psi Yes there is a leak and a rebuild may be needed.

 

most forks on motorcycles and trikes actually utilize 2 springs; the steel mechanical spring and an air spring. now this air spring isn't a physical thing, its the result of atmospheric air pressure thats trapped in the fork when you put the caps on. and because you can compress air, it acts like a spring. this "air spring" is used to setup and tune the stiffness of the forks. the way to measure this is with the oil height in each leg. this is measured by taking off the cap, removing the spring, collapsing the fork completely and then measuring the level of the oil from the top of the fork tube surface. the higher the oil height, the stiffer the "air spring" will be, and vice versa. pressure builds up in the fork because air heats up as it's compressed.

on your shock air pressure doesn't build up because the rubber bladder in the remote reservoir is filled with nitrogen and takes up the space in the shock that the oil creates as its displaced by the piston. this way the oil doesn't foam. the nitrogen in the reservoir doesn't build pressure because nitrogen is a more stable gas than air. on forks, to fight foaming, the manufacturers came out with cartridge forks in 86, on the cr's first. the cartridge separated the compression valves and rebound valves from the main oil source which was easily foamed. this created more consistent performance for motocross. your atc doesn't have this.

sorry for all the boring tech talk. your oil height should be 186mm, total capacity is 400cc. you can use 5w or 10w fork oil. you can also use ATF. i think its viscosity is around 10w.

 

hey man i just bought a complete front shock set off a 85-86 250r so now i have two i could just sell you one of mine if you want. my email is taylerj2389@yahoo.com i will sell to you for cheap man real cheap.