| Author | Message | ||
     Audiowize |
I searched a bit and consulted the FSM, and I'm not seeing an answer to my question. The crankcase is vented out through that reed valve that admits said air into the cam gear casing. When the pistons are moving up and the reed valve shuts, from where is air under the pistons resupplied? | ||
| Ducbsa |
You want a vacuum there, so no air should be re-supplied. Race car application: http://www.jegs.com/p/Moroso/Moroso-Racing-Vacuum- Pumps-Accessories/745524/10002/-1 | ||
| Audiowize |
If there was no supply for additional air, there wouldn't be any real flow out of that reed valve at a certain point, and that doesn't seem to happen. | ||
| Greg_e |
The PCV is really to get "stuff" that blows past the rings. If that never happened, I don't think we would be having a PCV system at all. | ||
| Livers |
Pulling a vacuum just implies that there is less than atmospheric pressure in the crankcase. Still plenty of air plus blow-by to open the reed on the down stroke. | ||
| Audiowize |
Interesting, I had never imagined that there would be that much blow-by, but that certainly answers my question. Thank you. | ||
| Sagehawk |
I really like these types of threads. thought provoking they are! There isn't a lip seal on timing side of crankcase so there is some regurgitating of expelled air from the reed valve back through the crank bearing. also , there is a oil jet that sprays underside of piston. It's conceivable that on a long hot day, your oil will get aereated and introduce some air into the crankcase area as well. Also add any blowby by rings to mix it up. In the end, even a negative pressure is pressure and generally if there are open paths within different parts of motor, I would think the pressure would try to equalize. like when pistons come down , reed valve opens and burps to timing chest, but there is the opening thru the bearing. Liquid may not go through spinning bearing but the pressure will, however minute amount it is. So, these crankcases never really go full vacumm while motor is running. I can go on a leisurely ride with wife and not have anything but condensate in catch can. I can go for a ride and really press the bike hard for 200 + miles and then I'll have oil blow over in catch can. when it clears and back to leisure riding back to just condensate in catch can. Now to go on a tangent, I have a 278,000 mile mazda truck that has a fresh air inlet to the crankcase that goes to a pcv valve that sucks crankcase air into the intake. why don't modern motorcycles have a fresh air inlet to crank case as well? I don't race my Buell so I don't need 100% Horsepower and all the Hype that goes with it. Yes , I want my rings to seal but I don't think that they won't just because I don't have a 100% vacumm under neath the pistons. I have said enough to take up my share of thread but I'm just sharing my opinion. | ||
| Ducbsa |
Sage, the pcv is a one way valve that allows the suction in your intake manifold to draw air out of the crankcase and not allow air back the other way. | ||
| Audiowize |
I do have to say, you guys are way, way more polite and informative than the members of the "other" Buell forum I used to post on! That reed valve seemed a lot like a PCV stuck down in the engine, I was just used to the PCV system having a pretty limited role in engine operation and being more functional in the sense of emissions. | ||
| Sagehawk |
Audiowize, thanks for the compliment. Life's to short to be that guy. Peer pressure works best and I've heard there have been several here that finally just went away. Ducbsa, true that on pcv seals after gas passage thru it. Nothing is perfect and if the foam in valve gets all gunked up then it wouldn't be as effective. Have you seen the really small holes at bottom of valve? I'm curious if they could pass enough air if running at high rpm or a big bore kit. All I know is I run a catch can with two hoses to it and a vent hose from the can to atmosphere. When opening drain, you can always feel the pulses of gas coming thru. So thread goes full circle. Where does all the extra air come from or is it some recirculated air? Anyway, I cut one of the pcv valves in half several years ago and I think it's still in toolbox at work. I'll look tomorrow and see bout posting some pix of it. I've thought if there was any advantage to running a vacumn line from emissions port on throttle body to my catch can to pUT a vacumn on breather system but have a place for oil to drop out. I would also plug off vent on can for this. I do know when breather hoses came out of intake it seemed bike fueled a lot better. Always thought that was best mod yet out of all I have done. | ||
| Ducbsa |
Audio, the reed valve is a pcv and all such valves are intended to minimize oil vapors getting into the atmosphere plus minimize crankcase pressure. With a bit of a vacuum in the crankcase, the pistons has less work to do, not having to compress air on the downstroke (called pumping losses) and making more net horsepower. The oil fumes don't burn so well in our motors, but in a modern water-cooled car engine, the tolerances, etc. are tighter and less air gets past the rings, etc. and the O2 correction in the fuel injection controls compensates for the oil fumes in the gasoline/air mixture in the combustion chamber. | ||
| Sagehawk |
Pix of my breather valve.   | ||
| Nillaice |
cool pics!  | ||
| Sagehawk |
I wanted to see how they were built. If you have a lot of crap going thru , I could see where sponge would load up and possibly plug up some. The valve itself may last longer in these due to not seeing the heat that my evos see where they are mounted directly in rocker cover |
