fork springs and oil level

[clw]

Yesterday I helped lower the fork level on a friends bike. It's a '00 YZ. Two things: 1. One fork spring had a coating of rust! How does something rust in an oil bath? Should anything be done? 2. The oil level measured about 95 in both legs, on a fresh oil change is the oil level (after filling the tube all the way to the top to get oil between the inner and outer legs) measured in the same way? Seems I heard that the oil level after a fresh change will measure different as soon as the fork is used. Is there a formula or procedure so we can put the oil level back on a fresh change to wherever we end up after we tune? Does this make sense?
HELP!

 

[Jeremy Wilkey]

CLW,
First thing you can do is totally overfill, or you could empty the volume by exstending the fork and adding 10-15mm. Its your call. As for the oil this is a by product of the natural chemical degridation of fork oil. Mineral based fluids (most fork oils) in particular will become very acidic as they aged.

Secondly your from florida, If I recll, and I would imagine you guys have alot of mositure in your air and that does not help either.

Stock KYB forks used to rust horibaly some peopleI know think its the oil, I don't really cafre to venutre to far as top what the cause is with the stock situation, but keeping your stuff serviced will definelty help.

Regards,
Jer

 

[Jeff Howe]

I have not seen too may rusted springs but I have seen some nasty rust on the steel cartridge rods of the KYB's.

 

[Jeremy Wilkey]

Shocknut,
Dude what do think caused all that rust? We've both seen it in Brandnew bikes?

Regards,
Jer

 

[clw]

10-15mm; is that the difference between the "already been used" and "by the yamaha manual" methods? So, to duplicate 100mm as measured you would do the book method and adjust to 110-115?

 

[Jeremy Wilkey]

CLW,
I don't know the Yamaha method..


Regards,
Jer

 

[Jeff Howe]

Honestly I don't know what causes it, but Ive seen it plenty bad. I got to wondering if it wasn't condensation, like from riding on cold days. I know one that I had from SD was BAD, and they ride in some colder temps out there. I've seen it bad enough to rip the rod bushings to pieces, and I remember one YZ 125 you pulled apart on my first visit to your place like this. Remember that one, gawd it was bad??

Oil plays a part in this somehow. One thing though...there are some refining processes going on that are creating extremely high quality mineral/petroleum based fluids that are highly resistant to oxidation now days. Hydrocracking is something new in that, and I guess there are some European companies that have taken it to further levels...termed Molecular cracking or MC. These processes appear to produce basestocks that will perform on a level with PAO synthetics.(which are noted to be the bomb in synthetics) Good idea to stay away from the cheap low grade fork oils, they won't last long.

 

[clw]

Yamaha manual method--fill the fork to the top (overfill), get all the bubbles out of the cartridge and elsewhere and then suction out from the inner tube only without pumping the fork anymore. If you set the height this way once the oil is released from between the inner and outer tubes some fills the inner tube and gives adifferent reading. Question?--how much different?