Frothy gear oil '85 K100

Hi all,

My '85 K100 has been shifting "different" lately. Clunkier when cold, and missing shifts more often. The clutch splines were lubed less than 4,000 miles ago, and the tranny oil was changed at the same time. The other day I thought to check the level of the tranny oil and found this: see attached.

The gear oil (Valvoline 80-90) is white, frothy, reading at twice the maximum level, and the consistency of a very wet cappuccino (hey, I'm from Seattle). By the way, when I took this picture I was just back from a 45 minute hiway ride in high forties temperature, but the oil looked the same this morning when checked cold. Also, I do have minor weepage out the drain hole under the transmission, but according to my searches this isn't uncommon in K Bikes.

I will, of course, drain and replace the gear oil as soon as possible, but any thoughts would be appreciated!

Looks like water mixed with the transmission oil. If it were me, I'd change the transmission oil immediately. I'd also look for potential sources of ingress of water and replace cracked or torn rubber seals.

I'll bet a dollar to a doughnut that you have a split/cracked/torn clutch rod boot. BTDT.

Ralph Sims

Drain and refill the gear oil immediately. Go to a pharmacy and get a few ounces of glycerin and add it to the new gear oil. Glycerin does for oil what Heet does for gasoline - absorb moisture (old North Dakota winter trick). Ride the bike long enough to fully warm up the transmission. Drain the new oil and replace it again.

Hope no bearing damage has occurred.

You boys are scaring me.

Drained and refilled tranny oil. Off to buy some glycerin (keep them tips from the heartland coming!). Then to the oil store.

I don't see any obvious areas of water penetration. There is slight evidence of oil weeping from the bottom of the forward seal, but nothing that screams water intrusion. Also took a good look at the clutch pushrod boot, and other than needing a bit of a scrub it looks to be intact. I will clean and inspect it more thoroughly.

What, I'm afraid to ask, are some of the classic symptoms of bearing damage?

Thanks!

I wonder if the water is coming in the breather vent , if the vent cover is missing?

I've seen this happen if a bike is used in a damp environment for short rides where it never really fully warms up. Unlike later models - the K bike doesn't have a heater built under the transmission (no cat-converter), and the transmission only heats up with heat from the engine. As it warms up a bit - the air in it expands (hence the need for the vent) - and when it cools down the air contracts, and if there is a lot of moisture in the air (we're talking Seattle right? WetLeather area?) it gets sucked in with the air, condenses and falls into the oil.

It's unlikely that any seal is letting the water in unless you're missing the cap on the vent at the top of the transmission. The drip from the hole in front of the transmission usually indicates a bad/petrified O ring behind the big-nut on the clutch assembly, and usually has nothing to do with the transmission.

If possible - take it for a nice long ride and let it get good and hot. When the transmission is really uncomfortable for you to put a bare hand on, it's boiling off the absorbed water vapor. That's a good thing.

minor weepage...

Looks like you are on the way for the current issue, and the minor weepage is telling you that you probably have either engine oil or trans gear oil getting past their respective seal. Early warning sign that a seal replacement job is coming. Best to do before it contaminates your clutch. How minor or not determines the urgency. If you are actually getting drops, smell it and see if it is engine or gear oil, and then proceed to prep for that job. There are many threads on this, and complete instructions on how. It is not that hard, just takes time and patience, and maybe a friend or two. Doing it yourself makes a $1500+/- job about $100-400 depending on whether you need a clutch plate or not.

Could it be that it was just over filled and is not being whipped into the froth you see there? Same thing that happens in the crank case when motor oil levels are past.

Do you know how much oil was added when it was changed?

I know that the gear oil level was within spec, as I topped it off myself after the mechanic's service. I'm still a bit flummoxed as to how so much water got inside, but I'm kicking myself for not checking it earlier. I completely disregarded my father's cardinal rule for the fixing of any problem: "first, jiggle the handle."

I will certainly troubleshoot the breather cap, but haven't located it yet. An online search and my Haynes manual yielded only conflicting advice and a wonderfully unhelpful picture. Can one of you give me a heads up?


Cheers gents!

abharding said:

I know that the gear oil level was within spec, as I topped it off myself after the mechanic's service. I'm still a bit flummoxed as to how so much water got inside, but I'm kicking myself for not checking it earlier. I completely disregarded my father's cardinal rule for the fixing of any problem: "first, jiggle the handle."

I will certainly troubleshoot the breather cap, but haven't located it yet. An online search and my Haynes manual yielded only conflicting advice and a wonderfully unhelpful picture. Can one of you give me a heads up?


Cheers gents!

Click to expand...

The breather cap is a little black knob located directly underneath the battery tray.

You may be able to peek in from the left side to see if the black cap is still in place.

Actually, it's at the very front of the tranny, on the upper left, directly underneath the starter.

If you get a flashlight and lay down with your head right at the riders left peg and look underneath the coil cover, you can JUST see it. The cap is black about 1/2" tall by 1/2" in diameter.

In this picture it's just past the tip of the light and looks grayish (but it's really black).

Thanks Lee, great visuals.

Sure enough, the breather cap is in place, with no evidence of problems. Meanwhile it's nice to have some smooth shifting action again with the replaced oil. Things have gotten a good scrub around the transmission housing, and you'd better believe I'm gonna keep a close eye on it.

Still wondering about the possibility of bearing damage. How would I tell?

Unless you hear some REALLY noticeable noises or feel some REALLY weird shifting problem, I would just keep an eye on the level and condition of the oil. I would give it another change in maybe 1000 miles and really look in the drained oil to see if there is any sign of metal.

After that, don't worry about it or you'll drive yourself crazy.

reviving another old thread.... Does any body know how tight the vent cap is supposed to be? In my struggle to remove the gearbox without taking off the starter first, I kept getting stuck at this cap. Now the gearbox is off, the cap is very wiggly and I don't know if that's the way it is or I damaged it when I kept yanking.


Dealer parts lady says there is none in stock in the US. It will take 2 weeks to get the part from Germany... But it's only $1-2.

It just snaps on. You can take it off by pulling straight up. It's normal for it to be wiggly as long as it won't easily fall off.

Thanks Lee. My is very loose. But I think because it sits under the starter, it won't clear the space to fly off. I just was thinking I may have broke it.

as an old SFK bearing guy..

Modern bearings tend to outlast the machines they support. I wouldn't be too concerned.