Why does used fork oil smell like sewage?

Maybe in my next life

I was working on my old 1975 Kawasaki KZ400, and when I ripped apart the forks on that bike, you can only imagine the stench from that fluid. 30+ years of riding on the same fluid.... oy.

That's the one.

And just a comment, there's the lazy way to change fork oil - and if it' ain't smelling like sewage it saves a LOT of time. (If it's sewage you need to strip the forks down and clean them)

Just take the caps off, drain what you can ( use a transfer pump from the top if need be) and top up to the correct level with fresh oil, but do it OFTEN. Takes about 5 minutes compared with several hours needed to strip the forks down properly - well worth $10 spent on extra oil.

Pete

Yes, that is a fast way to replace fork oil. Though you won't ever get it all out, and there is no way to determine proper and equal amounts in each fork unless you remove springs and measure air gap.

Once the forks are off taking the caps and springs off takes and addition few minutes, so why not?

Proper and equal is easy. I have a bamboo skewer in the garage with tape around it I use as a refill marker. Do it properly once, measure and mark it once with the front fully down and the springs poking out.

Next time loosen the top clamp bolts, undo the caps, push the front of the bike down, pump the oil out that you can get at from the top (~2/3) (my forks don't have lower drain holes) and refill with fresh to the mark. Put it back together.

5 minutes every six months is a LOT less effort than several hours every two years, and I'll bet on average my oil is in better condition than yours. It's not engine oil (where this would be a bad idea) it ages totally differently.

Pete

You won't ever get all the contaminents out that are sitting on the bottom.

I had a neighbor for several years in San Jose by the name of Jim Lindeman. I talked to him several times about replacing fork oil. He argued very affectively that there is no way to get the proper amount of fork oil in each fork unless you remove the springs and let gravity and piston action drain as much as possible, then remove damper rod and compress forks with hand over open end to use air pressure for force in new fluid. He seemed to know what he was doing.

You bet your fork oil is in better condition than mine? It's not a competition. There is a right way and an easy way to do things. I can, and do, change fork oil in my bikes in about an hour, start to finish, and the experts say this is the correct way to do it. I will spend an hour every year at (least) to know my front suspension is fresh.

of course, I'm nobody to argue with bamboo and tape.

Me too

Pete

(Anything works better than waiting until it smells like a swamp though)

Ever work in a machine shop? Any machine using cutting fluid can end up stinking like rancid butter in a very short time. There are additives that are supposed to kill off bacteria, but even that doesn't totally solve the problem.

At one facility I worked at there was a sudden shut down, and despite the machinist's advice to clean up and drain the machines, they were told to leave things and get out. After a month long shut down the entire place smelled like a cross of rancid butter and rotting fish...and that aroma would bond to everything...and hair in particular. It got better after a while, but never really vanished entirely.

There are some pretty strange anaerobic bacteria that can grow and multiply in some pretty bizarre environments. Anaerobic bacteria tend to give off methane as a waste product. (Aerobic bacteria tend to give off carbon dioxide. Facultative bacteria can live in either aerobic or anaerobic conditions and can give off either gas - tricky!)

I always figured that heat and fluid/mechanical action killed off bacteria, but a few always survived, and they would just feast on the dead ones and the population would explode again. Even the original oil isn't added to the forks in a "clean room". Always going to be a few little critters getting into the system somewhere.

Not that I think they're involved with "Original Jap Fork Oil Horrible Stench", but one real nasty anaerobe, a sulfate-reducing bacteria (SRB, formally known as Desulfovibrio desulfuricans), makes H2S (hydrogen sulfide). Methane gas in farts may ignite, but the strong "aroma" is H2S.

Take a look:


Abstract

The corrosion of sewers and the control of odor are the major operational and maintenance problems in wastewater collection systems. The generation of hydrogen sulfide and subsequent sulfuric acid results from microbially mediated reactions, by sulfate‐reducing bacteria (SBR) and sulfide‐oxidizing bacteria. This review covers pertinent information about sulfate reduction‐induced problems in general and SBR in particular. Metabolism with respect to carbon, energy, and sulfur sources, ecology, growth factors (dissolved oxygen, temperature, pH, and sulfide), and the competitive effects of methane‐producing bacteria on SBR are discussed. Because metals react with sulfide to form metal sulfide precipitates with extremely low solubilities, metal interactions in sulfate reduction environments are discussed.

http://www.tandfonline.com/doi/abs/10.1080/10643389609388489

I'm wearing a hazmat suit the next time I change fork oil...

Bingo.

RIP Jim.

Yep, he was a good dude.

Another thing to think about with this method. Bike is sitting in the garage. While sitting, all contaminents settle to the bottom. Someone sucks up the top 80% (and that is very doubtful) of fluid, it's simply removing the BEST fluid, and replacing it with some slightly better. All crap is still at the bottom. Every fluid change I've ever done doesn't get rid of the junk until the last ounce or so, which tells me this does nothing but let crap accumulate over the years.

Not to mention taking out spring and changing/inspecting seals is a good time to look at all the internal parts.

The crap sitting on the bottom is fine, it's settled and it's not going anywhere unless the bike is upside down and bouncing down the road (And if that case I'm not caring about the crap damping). Until that crud gets 'quite deep' it's better there than stirred through the mix by a half arsed attempt to get it out.
(And quite deep crud in the bottom is the same as smells like sewage, not arguing that a real clean there isn't needed).

Use protection (for the sliders ) and frequent oil partial changes are good enough. It's not a race bike where I'd be dicking with the damping to set it up for a particular track.

Not saying your method might not be 'better' but it's like changing engine oil more often than necessary. Yeah, in theory better, but in practice there more chance of making a mistake as well.

(Now where's that asbestos suit).

Pete

That's just rationalisation, to avoid taking the forks off. :)

Forks should be disassembled the first time and cleaned well. After that, just drain and refill. Fork oil really has an easy life compared with engine/trans oils.

I still want to fart in the face of the engineer(s) who decided we no longer needed drain plugs in forks. A heavily festooned 860 lb. cruiser is just a crazy waste of my time to REMOVE the fork tubes, rather than simply draining. :ddog

Wow, I thought it smelled like sewerage cause I kept pouring liquid poop into my forks after eating pizza and drinking beer all night. Crap always ended up with that greazy sheen the next day, figured it had to have some good lube component to it.

I knew a machine operator that got a nasty infection machine coolant. He may have been immune comprised in some way, but there may be critters that live in oil that can hurt you. So wear gloves and be careful.

Rod

Amen. Even on lighter bikes it's a pain.

That's why I came up with the lazy bastards workaround in the first place.

Pete