Why does used fork oil smell like sewage?
 

Just R&R'd the forks on my Ninja 250 to flush them out and fill with fresh oil. Bike has 15K on it and is a 2007 -- first time I've touched the forks on it.

God almighty that shit smelled terrible! :puke2 Hard to believe that oil in a relatively sealed environment can get so disgusting! I don't get where the sulphur/sewage smell comes from -- I noticed this on my VFR a couple of years back working on those forks. Is it something in fork oil that "goes bad?" Yellow metals in the bushings?

Ever drain the 90 wt out of a work truck?
Stench to make a buzzard cry.:eek1
I've seen additives to give a grape odor to gear oil so it aint as bad the next time:lol3

Yes I've had my fair share of dealings with gear oil :puke2 That stuff will always be the reigning king of terrible smelling fluids. That stuff even reeks when it's new.

People used to joke that the Japanese OEM fork fluid was some kind of fish oil.

Maybe it's not a joke. :lol3

Is the oil hygroscopic? If it is, that would explain it.

The second time you drain your forks, the oil will smell just like it did when it was poured in. :1drink

Musta been some moisture in there at some point. Condensation/humid air at the assembly plant maybe? Done my Sporty and Buell on multiple occasions, and I don't remember it being funky at all. Hmmm...

Outta try combining Harley's Formula Plus in the primary with a bad stator, and it's just about garage clearing fumes.

I did a '99 250 with 16k on the clock last night at the shop and it was the same as you describe. Id say 80% or so of the forks I do stink BAD. Not sure what it is, but its there!

When I have customers in the shop I have them smell down a fork that Ive just popped open - thatll stop them from thinking about tacking a rebuild themselves :evil:rofl

Only takes one time to remove the little phillips head drain screw in the lower side of some forks w/o first getting the weight off the wheel.

Amazing how fast and far that stinky crap can spray. Don't even think about getting your wife/GF to wash your pants with any other clothes.

It is whale oil.....think about it. No really!

In the '50s & '60s there was whale oil added in ATF.
At one time it was considered the best watch lubricant.

Traxxion states, it is best to change road bike fork oil every two years or 10k miles.
Race bikes, dirt or track, should be changed quite often. The impact of fresh oil is felt.

Cleaning the fork internals can be tough. Better shops use ultrasonic cleaning.

The stink?
Alot of heat is generated as the oil is forced through the orifices. This causes it to degrade over time.

While that is one way to change the oil, I wouldnt reccomend it... its not the proper way as it doesnt get all the fluid out of the fork, or the actual nasty gunkiness in the damper rod/cartridge. Any fork service I do the forks come completely apart:

Ninja 250 example:

Lower Fork Housing
Chrome Fork Tube
Spring
Spacer
Washer
Fork Cap
Damper Rod
Top Out Spring
Valving Assembly
Inner & Outer Bushing

Everything goes into the parts washer, cleaned, dried, fork tube polished, new fork seals and fluid, and buttoned up with the top joke of a retaining clip replaced with a proper stainless steel C-Clip - makes changing fluid or springs next time a snap.

There is nasty, nasty gunk in the valve stack and at the bottom and inside the damper rod that a simple drain and fill will never get, instantly contaminating the new fluid.

Sorry, didnt mean to turn this thread techy, just wanted to make sure people knew that just because theres a drain screw on some forks doesnt always mean thats how it should be done.

ever smell ford friction modifier for use in limited slip rear diffs?:eek1

15k is too long for the first drain.

put some race tech fork lube between oil seal and dust wiper...

'Relatively sealed' is not completely sealed. Five years is too long. Replace it in a year as it should be on a bike ridden somewhat often and it will look and smell like new, and ride like new...or better.

Not really, and even if it were, how would water get in?....

Dunno about the Eurocrap, but OEM Japanese fork oil always smells like bait that's way past its' pull date, and if you wait a few years it just gets worse.