Do You Really Need to Change Fork Oil? 1992 K100RS

[BCKRider]

If you have replaced fork seals, changed the fork oil, and also added gaiters so dried bugs on the forks can no longer mess up the seals - well, why change that oil every year or even two years?

When I did do it annually on my K75 (after all three above) what I drained looked exactly like what I added. My K100 now has a couple years with the same fork oil (again, after all three above) and just wondered if this is a little job I can safely skip. And for how long?

BTW, I've heard fork seals last basically forever when you use gaiters. If so, what other bad stuff can get in there?

As always, I'm sure I'll get some good advice from the knowledgeable people on this forum.

[PGlaves]

Gaiters (properly installed) are good. They keep out the debris. Seals do last almost forever. Gaiters are vented, so eventually you can get some moisture in the oil. I think annual change is/was overkill, but still don't consider it permanent. I think it depends on both time and miles. Every 2 or 3 years might be about right if you ride quite a bit.

[moondog]

yes

[GREGFEELER]

I have gaiters on all but one of my bikes so I see some pretty clean oil during my fork oil changes. I do follow the mileage recommendations, but don't always do it annually. I figure any place there is a lubricant and a possibility for contamination you need to change the fluid periodically.

[roncooper]

I had been doing mine annually until this year. It always looked clean, so I skipped it in Feb. If it looks bad when I do it next Feb, I'll report it here.

[deilenberger]

Doug,

Please see: http://www.bmwmoa.org/forum/showthread.php?t=46057 - I'm adding the info to your thread title.

I think Ron's idea is good. If the oil looks different when it comes out then when it goes in - it needs changing. If not - probably not.

While I doubt if much moisture can actually get into the forks - with the pumping up and down it's possible some gets in (unlike some bikes that use pressurized forks as additional springs).. and the moisture might contaminate the oil. The viscosity of the oil may also change just due to shearing action as it works through the passages that provide damping (usually holes in the fork assemby, sometimes on cartridge forks, holes with flat springs over them that are forced out of the way on movement.)

[bikerfish1100]

i am going from what i have gotten from talking to the guy that has rebuilt my rear shock the last 3 times- the oil itself wears out from use. not from contamination, just usage. he said mine smelled and looked prety nasty after ~35K miles, and recommended changing it at closer to 25K.
if that oil gets bad from usage, and motor/trans/Fd oil does as well- why would we think that fork oil does not?

[BCKRider]

Thanks, guys. Is there some consensus that "three years or 25,000 miles - whichever comes first" would be safe but not ridiculously so, provided you have properly installed gaiters?

Don, the year and model of my bike appears below my name at the bottom of every post I send. Actually, I wondered about sending my OP to the K-bike forum because I think the question applies just as much to airheads and possibly other BMW bikes. If you know how this question could have reached a larger segment of the online community who would be interested and could benefit from this sort of informed opinion, I'm sure I'm not the only person who would like this information.

Again, thanks all.

[David13]

Once in a while, I say. Depending on what things are looking like. A dirty dirt bike, more often. A clean road bike, less so, if the forks are kept clean.
But seals do not last forever.
If a bike sits the seals will dry out and crack and crumble.
They disintegrate as it is, as does rubber hose. Which is why fuel line needs also to be replaced when necessary, but definitely if it starts to harden.
On the forks, the seals will disintegrate and drop rubber particles into the oil, causing faster disintegration.
So I think it depends on the bike. I think it could be anywhere from two years to seven years.
But it should be done.
dc

[35634]

A little off topic, I blew a fork seal and found this spacer in the bottom of the slider. The remaining oil looked fine. I'm guessing the non-gaitered seal was letting in water before it blew. Never would have notice it if the spacer hadn't slid out.

[GREGFEELER]

Not to beg the question, but just how much work is changing fork oil? As stated earlier, I have gaiters all of my Klassic K-bikes and change my fork oil every 6,000 miles or two years. If it ever comes out less than clean I figure I've waited too long, or have a contamination problem. However, I've also changed fork oil several times in a day testing different weights and refill quantities to get the fork performance I want, and it didn't seem like a big deal to me. Just sayin'

[roncooper]

I had been doing mine annually until this year. It always looked clean, so I skipped it in Feb. If it looks bad when I do it next Feb, I'll report it here.

I just changed it and the normally dark purple BMW 7.5 was nearly black. I will go back to annual changes.