Adding Oil to Forks??

[Lou Ranger]

I recently read on a Honda Nighthawk site a tip from an old bike mechanic. He was responding to someone who was having air leak out of the front forks - the Honda had adjustable forks using a valve and compressed air.

The mechanic said that he eliminated the need for any air pressure to firm up his shocks by inserting about an inch of plastic piping inside the top of the forks. This length of pipe pre-loaded the forks instead of having to rely on pressurized air (which routinely leaked out) and he claimed, as a result, they performed at 100% all the time instead of a gradual decline with air leakage.

Could that same principle work on xs400 forks - i.e., allow one to increase stiffness of the forks?

 

[Scorpio1963]

Sounds like a very interesting concept LOu,This preload piece would need to have a cushion stopper other wise once the preloaded pipe reach it max up and down travel it would be like hitting a hard bump would it not?

 

[XSLeo]

Some forks come with a spacer above the spring, some don't. Adding a spacer or making a longer one is how you adjust the spring preload.
To determine if you need to do this is with the bike setting with no load held up straight measure from the center of the axle up to the bottom of the lower tree. Now with some help carefully mount the bike. Now measure the same as before. subtract the second from the first. This gives you the laden sag. For an easy ride it should be around 35 mm. For a more sporty ride it should be around 25 mm. If more than 35 mm add a spacer to bring it up to the 35mm sag.
Your rear shocks should have the same sag, Measure from the axle up to a spot on the frame straight up from the axle. Adjust the spring preload by turning the outside of the shock.
Once you get the preload set, with the caps off the forks and springs out. forks collapsed, add oil to the forks till the level is 6 inches down from the top. I have a plastic hose for my Miti Vac with a zip tie 6 inches from the end. I add too much oil then put this clear hose down in the fork so the zip tie is even with the top, then suck out the extra.
This will be more oil than stock specs, but gives a better ride with better steering control.
Leo

 

[pupulek]

Howdie, Iam on my way to fix my forks but I have not figured out the amount of fork oil to put in. in "liter" please

 

[Lou Ranger]

Howdie, Iam on my way to fix my forks but I have not figured out the amount of fork oil to put in. in "liter" please

Welcome to the Forum.
The amount would depend on which model you have.
From here (http://www.xs400.com/forum/forumdisplay.php?f=2), go to the first thread and refer to the manual for your bike. Fork oil capacities are included in the body of the text which outlines the procedures. Good luck!

 

[john slaughter]

Hello- I'm new, just acquired an '82 xs400, and the forks seem to need oil, I understand the orthodox method of removing the hardware on top (circlip and spring cap) but fear of flying circlips and springs prompts the ?? what about injecting oil into the drain hole? The structure above is not airtight, or else you couldn't add oil from top anyway, so no bleeding would be required. What do you all think?

 

[Lou Ranger]

Welcome to the Forum.
I had to put oil in the forks of the Yamaha I had before the 400 using the drain holes.
All the springs and clips in the top of the forks were completely seized in there. It was also effectively airtight - I tried adding oil above hoping it would seep down but it did not.

I came up with a work-around which (sounds crazy but) worked really well - posts # 11, 25, 28, 30 on this thread:

http://www.xs400.com/forum/showthread.php?t=8139
​

 

[xschris]

You need to remove ALL the old oil before adding new. These need to have the correct amount in each tube. If you caps and seals are bad, replace them so they can work proper.