Burning Gear Oil

PE175 · Mar 7, 2004

Today I decided to change the oil in my YZ125 and I noticed that there was barely any in the gear box. Anyway I filled it up to spec and started the bike. When it started CLOUDS of smoke started coming out the pipe and spooge was getting everywhere. BTW I made sure not to overfill it.

Just great. Is this a Crank seal or something? Can someone give me an idea of what this is? Is this fairly easy? I am rather mechanically inclined and have a factory service manual for this bike. Any help would be appreciated.
Thanks

darringer · Mar 7, 2004

It's the right side crank seal. Engine is drawing in tranny oil through the crank seal and burning it, giving you the smoke screen. Remove the clutch cover, and remove the primary gear to get at the seal. With the manual it's a fairly easy job.

j_freak · Mar 7, 2004

My MR175 burns tranny oil too. It has a small leak in the gasket between the two case halves. Makes it smoke and spooge a lot, but I cannot get a replacement gasket (and if I delve that deep into the tranny, I'm afraid I'll find a bunch of other broken/cracked/mangled parts that need replacing...)

But if this started suddenly and it's a lot of oil, it probably is the crank seal.

j_freak · Mar 7, 2004

Spray wd-40 on the carb intake boot and on the seal under the flywheel. If the rpm's change when you spray a certain spot, that's where the air leak is

j_freak · Mar 7, 2004

Oops, please ignore previous post, I hit the back button one too many times...

PE175 · Mar 8, 2004

Also the bike revs uncontrollably, I have to have the idle screw almost all the way out for it to even idle decently

billtx · Mar 8, 2004

I have a 99 YZ125..crank seal went bad. You can change the right side seal without splitting the cases if your handy. However your crank bearings are probably worn out also.

mxmatt426 · Mar 8, 2004

billtx is right, there are reasons crankseals leak. It would be a good idea to replace the bearings.

j_freak · Mar 8, 2004

PE175 said:
Also the bike revs uncontrollably, I have to have the idle screw almost all the way out for it to even idle decently

:eek: Well, in that case, do not ignore my previously previous post. Spooky :cool:

PE175 · Mar 10, 2004

Can anyone give me a parts list I should have? I take it I have to split the cases?
I'm thinking both oil seals, new crank bearings, gaskets, is there anything else?
Thanks.

billtx · Mar 10, 2004

You probably should either replace the crank or have it rebuilt since the lower rod bearing is most likely just as worn as the crank bearings.

If you a have a local friendly dealer they will inspect it for you when you have it apart to make sure nothing else is worn - assuming you are getting the parts from them. You don't want to go through all this and have to split the cases a few months later. On a '91 you probably have other things that are worn and the part costs is small vs time and effort to replace.

billtx · Mar 10, 2004

Even easier..just send the engine to Forward Motion/Eric Gorr. I have not personally used him (yet) but many folks here have and they feel he does great work at an honest price. Sometimes doing it yourself is not the cheapest.. I know!!

Good luck.

PE175 · Mar 10, 2004

Hmm well I think I'd rather do it myself, it's something I'd like to learn and need to seeing how I've been riding my whole life and have never done anything to the bottom end of any bike... I"ll take the crank to the dealer... If it is damaged I will guess I'll just have it fixed.

Burning Gear Oil

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