I've seen posts about this before. Now it's happening to me. Searched no good results.

Over the last 2 weeks vacation I had some oil coming out the breather tube. It's enough to soak the top of the outerwear on the filter and drip down on the rear shock and swing arm etc. I have no air box. It seems to only do it on long hill runs at higher RPM's. I've ran high rpm's up hills in the past and haven't had it do this. Any reasons why? Cracked rings? Bigger bore causeing it? Any thoughts? TIA

 

Was the oil level fine? Just asking, I am sure it was. Was the weather hot? .

 

I've heard that if the rings are worn you'll get "blow-by" which effectively pressurizes the case and can force oil out of the breather tube. Maybe do a compression or leak-down test to check the health of the rings.

Not sure but something to think about.

 

Warm, 80's 90's oil level within specs.

The engine rebuild hasn't been complete long enough to have worn rings. 100 miles or less.

 

Hmmm...maybe, and this is strictly a guess, the rings are not "seated" yet and there is some blow-by. Not sure how long it takes the rings to seal best but after some more time on the engine they may seal better??

Sound reasonable or silly ??

 

I would think 100 miles or so would be enough. It only seems to do it when I rev high and for long periods of time, ie drag racing up hills and LS Utah has a very long one, thats where it started and Choke cherry and Devils dune are steep hills at St Anthonys Idaho that require me to be in the power for a good period of time also. I'll get it all cleaned up and see how it does on the next outing. I'll try not to hammer it so hard. LOL

 

What oil are you using? how much of it?

 

It may just be that the piston clearance and ring gap were set at the looser end of the specs. and
/or the ring gaps are line up or close together. Better to run things a little loose and buy a little oil than to have things break. Do you get anything out of the breather after the engine is warm and rev it?
I don't think it's anything to worry about but you could do a leak down test just to be sure.

 

Yamalube 4 from day 1. 2.4 quarts with oil filter change.

Well, the ring ends were set according to the manual. Doesn't mean they haven't moved or got moved some during install. I don't see anything when I rev it some in neutral.

 

Mine does this, too. I have been told it is normal.

Also, how long can you run the engine before your oil turns black? One good ride and mine is still thick and clean, just black. Just wondering.