[ace.cafe]

Yes, I noticed that as well.  I seem to notice all of the "crankcase breather mods" after I read ACE's write-up on that subject.  Looks kind of cool, but likely has the shortcomings he mentioned.

The UCE is different than the older model engines.
However, I would still say that the filter is not needed because there should be no air going IN there, only OUT.

[SteveThackery]

The UCE is different than the older model engines.
However, I would still say that the filter is not needed because there should be no air going IN there, only OUT.

Won't it go in and out, as the piston goes up and down?  Or is there an internal duckbill?  (I can't remember).

[ace.cafe]

Won't it go in and out, as the piston goes up and down?  Or is there an internal duckbill?  (I can't remember).

I haven't dissected that part yet, but as I continue disassembling this blown UCE engine that I have here now, I will know that answer.
However, my conjecture at this time is that there would be some internal device for controlling breathing. I'm sure there is at least an air/oil separator baffle, and perhaps a valve of some sort. If not, then there will be pumping losses of some degree there, and that would not be good in any respect, and there should not be air entering there for any operational reasons.

As has been previously discussed, the UCE wet sump design has much more crankcase volume than the old dry sump models, so that helps. But as we see from GHG's comment above, if the hole is blocked, he recorded pressure increase, so it needs to vent out. This is expected. But if it then takes air back IN, then that doubles the pumping loss and loses the advantage of negative crankcase pressure.

Soon I will see for myself exactly what is in there. I am busy at the moment with the other projects going on, but I will get to it. If I find a way to improve the system, I will.

[mattsz]

I'm surprised this hasn't been settled by now.  Neither the parts catalog nor the service manual show or mention a valve or anything which might control the breathing.  But there must be someone who has had that part of the engine opened up enough to know what's going on in there.

Looking forward to your discoveries, ACE...

[ace.cafe]

I'm surprised this hasn't been settled by now.  Neither the parts catalog nor the service manual show or mention a valve or anything which might control the breathing.  But there must be someone who has had that part of the engine opened up enough to know what's going on in there.

Looking forward to your discoveries, ACE...

It would not hurt it to put a duckbill valve on the breather outlet. It would prevent the return of any air into the crankcase, and it would not impede any expulsion function. So , in the interim, installing a duckbill would do no harm, and in the event that no other valve is present, it could have benefit.

[Ducati Scotty]

+1.  I think there is a labyrinth in there to keep the oil from splashing out but no valve.  Venting to the air cleaner as OEM does makes sure there is always some negative pressure and clean air getting sucked in if that happens.  I've had that side cover off many times and there is a gasket for the vent chamber, but as it was never leaking I never opened it to change it, so not totally sure what lurks inside.

Scott

[gashousegorilla]

   There is no check valve in the pub at the breather exit on the side cover, there is no check valve inside the breather chamber/labyrinth.   But it works. And I would be cautious about putting a duckbill or checkvalve, reed valve, Krank vent etc. On the end of that breather without  checking to see what it does to the pressure in the case..... You may get a bit of negative pressure?  Which MAY help slightly ?   Or it MAY add a restriction and increase the pressure.... not good.   I would  just check the pressure and see how it reacts with what ever you stick on there.


   I don't fully understand  how system works... But I do know that a restriction WILL increase pressure.   I think the way the system works has to do with the volume of the chamber, it's labyrinth design... partial Tesla valve?  , the inlet and out let locations of the breather and  oil level.   It does not let much air in at all.  You can test this by trying to blow in. And you will find  .... at least I did.... that you wont be able to get half of your breath out before it stops and you cant blow in anymore.  It seems like you are filling the breather chamber, and nothing beyond that.   And certainly, there should be enough volume in that entire Engine case to get a breath into.  Remove or loosen the the oil fill ?.... and you can blow in to your hearts content.     

 Again, I get zero crankcase pressure throughout the RPM range. and it acts as a one way valve.  One MAY at times get some negative manifold pressure on the breather through the hookup at the air box ?   Not sure, as I no longer have one. But someone should check that on a stock bike .......

[suitcasejefferson]

It seems to me that on a single cylinder engine, or a 360 degree twin, when the piston(s) go down, there is going to be a decrease in crankcase volume, which will create pressure, which has to go somewhere. When the piston goes back up, the crankcase volume increases, which would create negative pressure, and would require that air go back into the crankcase, or it would otherwise create negative pressure in the crankcase.

I went out and started my XT225, another single cylinder bike, and pulled off the crankcase vent hose. I couldn't hardly feel anything at the crankcase vent fitting on the engine. Loosening the oil cap however, created very strong pulses, definitely pushing pressure (and oil mist) out, and sucking air back in.

I am an auto mechanic (retired) and never had to deal with this situation. Truth is I never gave it much thought. But I would be interested in finding out how it works.

I would still like to see RE build a factory scrambler, for about the cost of the GT. I could almost for sure convince myself to buy one.

[Ducati Scotty]

It matters less in a car engine since they're almost always multi-cylinder.  Some pistons going up, some coming down, it helps to balance things out.  On a single with large displacement and a small crankcase, it's as bad as it can get.

I suspect you're XT has a one way valve which is why you didn't feel much at the vent but did at the oil filler.

Scott