Panhead Oil Separator and Screen Questions

[SeaHag]

I haven't got a good understanding of this yet after reading posts and looking at manuals so let's try to clear this up. The separator (hard curved metal piece with two 1/2" semicircle notches in back), from all the pictures I've seen, goes in arcing upwards with the two notches in back. The screen I've seen all but one pictures have it arcing downward, under the hard metal separator piece with a space between but not arcing upward against the separator. Only one pic I ever saw had the screen arcing upward against the separator. So I really don't understand how this system is supposed to work. On pistons down stroke air is forced thru breather gear into crankcase then thru timing cover out pipe into this "separator chamber" in the right case. Is the air supposed to go thru those two semicircle cutouts in the separator piece then thru the screen before it goes out the pipe to atmosphere? It seems the air can just go out of the timing cover pipe then right out the pipe that goes to the atmosphere without ever going thru the separator/screen combo. If the screen is not arcing upward against the separator then there is a big gap between the two where the mist can go and bypass the screen. And finally there is a big hollow area in the timing cover in front of the separator/screen where the mist can also go to bypass the separator/screen pair altogether. How is this crazy system supposed to work to separate the air/oil? It seems that the oil mist can go right out the pipe without ever using the separator/screen. And is the screen supposed to go right up against the separator or is there supposed to be a gap in between and why? I've built this bike from the ground up and this is the only part that has me stumped.

[Cotten]

SeaHag!

It is my feeble understanding that the screen and baffle were only "bubble busters", which have lost relevance with modern oils formulated with anti-foam agents (as have modern fuels).

Thus later models dispensed with them.

But I could be wrong again.

....Cotten

[SeaHag]

Thanks Cotten, that sounds about right. Seems like nothing to really worry about in this day and age. While we're on the subject I find it amazing that the engine can push two cylinders worth of air out of the case on the down stroke thru that little breather pipe that looks like about 3/4". This must make a lot of pressure in the case, then when the pistons go back up there must be a big vacuum. I know there is vacuum on the up stroke to draw oil out of that little hole under the screen in the separator chamber. Where does the case draw new air in from on the upstroke? Does the engine really suck in and blow out two cylinders worth of air from the case each rev? I'm talking about the crankcase of course not combustion. It only blows crankcase air out the breather, not in, right? Breather is closed off on the up stroke right? So then where does air come into the case on the up stroke?

[Cotten]

SeaHag!

Not all of the volume of the cases and cylinders is supposed to be expelled.
If the breather does its job, air is compressed within the cases to act like a cushion, and a spring to rebound the pistons on the upstroke.

Or so I was told.

....Cotten

[58flh]

seahag-----on the downstroke exhausting air delivers a oil mist-vapor to chain-which is regulated by screw on pump.The breather valve is timed according to downstroke of pistons!-this also will give scavenging oil a boost threw the crankcase into the camchest.You were correct i8n saying that the breather valve closes during upstroke,which creates the vacuum in crankcase. At that time the portin valve is closed-thats when the oil in breathervalve lines up with a pass in the crankcase, this is when oil is picked-up by vacuum from the oil-trap on breather,then recirculated to tank by oil scavenge passages. Its been awhile & early & im tired but I hope this helps out!.----58flh

[SeaHag]

If the breather does its job, air is compressed within the cases to act like a cushion, and a spring to rebound the pistons on the upstroke.

Ya again that sounds right, and after the rebound the pressure turns to vacuum at some point in the upstroke to suck oil back into the case and then provides the opposite effect of "sucking" the pistons back down on the next down stroke

Not all of the volume of the cases and cylinders is supposed to be expelled.

And now that I think of it if the pressure/vacuum in the case is equally balanced it's not going to be much.
but the small amount of air that is bushed out the breather each time must be replaced each cycle back into the case to be expelled next time. It's a one way flow of air. It goes out the breather but where does it come in?
As a side note, it seems that the pressure in the case would cause oil to leak out gaskets, maybe a good case for gasket sealer.

[Cotten]

If the breather does its job, air is compressed within the cases to act like a cushion, and a spring to rebound the pistons on the upstroke.

Ya again that sounds right, and after the rebound the pressure turns to vacuum at some point in the upstroke to suck oil back into the case and then provides the opposite effect of "sucking" the pistons back down on the next down stroke

Not all of the volume of the cases and cylinders is supposed to be expelled.

And now that I think of it if the pressure/vacuum in the case is equally balanced it's not going to be much.
but the small amount of air that is bushed out the breather each time must be replaced each cycle back into the case to be expelled next time. It's a one way flow of air. It goes out the breather but where does it come in? Maybe thru the generator bearing? the case is sealed everywhere else that I can think of.
As a side note, it seems that the pressure in the case would cause oil to leak out gaskets, maybe a good case for gasket sealer.

SeaHag!

You are presuming a steady-state, which may never occur.
While the motor is warming, there is expansion. Upon acceleration to high R's, the differential may even become insignificant.

I tend to believe it is insignificant when spread over the whole range of operation, lest these beasts would never survive at all.

....Cotten

[hogboy52]

..
This is absolutely not a pressure system. When the valve is open it removes air from the engine and when it closes the pistons go up and create a vacuum in the motor. The main function is to suck oil from the heads where ordinary drainage is too poor. Also it moves oil from the crankcase to the oil pickup. The 1969 manual shows how this operates.

Whatever is seen when turning the motor by hand, in regular operation the engine case is never over atmospheric pressure. At bottom stroke a small amount of air will be drawn into the breather a short distance then blown back out. The total air leaving the engine is that which comes from blow-by.
..

[SeaHag]

The total air leaving the engine is that which comes from blow-by.

Ah...and there you have it. That's where the air enters the case from. But when the two pistons go from their highest to lowest point isn't that pressurizing the case?

[58flh]

Seahag-----yes when pistons on downstroke it develops crankcase presure. It is this presure that travels threw scavenge passages in the motor,oil comes goes to chain,the rest gets recirculated. It is very easy if you have an exploded view of feed,&scavenge,&return system for oil!--58flh

[john HD]

don't forget your breather line to the oil tank.

additional space for air to travel back and forth.

john

[SeaHag]

Seahag-----yes when pistons on downstroke it develops crankcase presure. 58flh

And that would give the rebound/spring effect on the down stroke Cotten was referring to right? Ok so now you confused me, before you said;

This is absolutely not a pressure system.

Now you say there is pressure.

So it seems there is pressure on the down stroke and vacuum on the up stroke and there must be zero pressure at some point in the stroke near the middle right?

It is very easy if you have an exploded view of feed,&scavenge,&return system for oil!

It is not easy for me to understand crankcase air flow from oil flow diagrams. I have those, I'm not talking about oil flow, I'm talking about air flow. The diagrams always showed air going out the breather tube and I never knew where it came back in from. It's blow-by (which is about 1/14th gas right?). The crankcase pressure seems to go back and forth between vacuum/pressure every rev. correct?

I used to think (before this thread) when the pistons came down the breather gear opened and all that air (74 inches in my case) would go out the breather tube. Then I wondered how 74 inches of air would get back into the case on the upstroke when the breather gear was closed. But that's not what's happening. If that were the case there would be as much air going out the breather tube as there is going out the exhaust pipe and that's not the case. The way I understand it now is that the case oscillates between vacuum/pressure every rev and the amount of air that goes out the breather tube is the amount that blows by the pistons. Correct?

[SeaHag]

don't forget your breather line to the oil tank.

additional space for air to travel back and forth.

john

Ya what's the point of that? Is that to give pressure to the oiltank to help deliver oil to the engine?

[SeaHag]

I got it!

Here's some links to what we've been talking about crankcase pressure and a device to deal with it. I may get one;

http://www.patentstorm.us/patents/58816 ... ption.html" onclick="window.open(this.href);return false;
http://ip.com/patent/US5881686" onclick="window.open(this.href);return false;

[SeaHag]

...I may get one

Or not.

http://www.nightrider.com/biketech/crankvent_test.htm