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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (http://xlforum.net/forums/showthread.php?t=2073932)

Tomcatt 7th August 2019 22:54

Quote:

Originally Posted by dieselvette (Post 5768345)
Attached pictures - let me know what you think...

I think that if the oil did what you show it would be picked up and pumped out by the scavenge pump and wouldn't be doing what you show.

At 6.000 rpm the surface speed of the crank wheels is ~200 mph. Think oil is going to sit as you picture it in proximity to the crank? Wet sumping kills power when it happens because the oil is whirling around WITH the crank wheels and isn't down at the scavenge pumps' pick up point getting pumped out.

dieselvette 8th August 2019 01:55

Quote:

Originally Posted by Tomcatt (Post 5768358)
I think that if the oil did what you show it would be picked up and pumped out by the scavenge pump and wouldn't be doing what you show.

At 6.000 rpm the surface speed of the crank wheels is ~200 mph. Think oil is going to sit as you picture it in proximity to the crank? Wet sumping kills power when it happens because the oil is whirling around WITH the crank wheels and isn't down at the scavenge pumps' pick up point getting pumped out.

Well, I think you and Hippy are both right, but how does it get to that point? I mean it makes total sense that the oil is flying around in there and NOT at the sump inlet, but what caused it to not get there? Was it accumulated in the bottom /front of the oil pan instead of the back? Why?

If there's too much air in the CC is it just so violent that everything flys everwhere but not to the sump? Or does wetsumping not happen at all at higher CC pressure unless other problem?

If there's too little air in the sump there is not enough draft to push the oil to the back?

Hippysmack 8th August 2019 01:59

Quote:

Originally Posted by dieselvette (Post 5768345)
Attached pictures - let me know what you think - filename is description for each.

I don't think it's density of oil/air mix, so much as density of air (with or without oil in the mix). Not pictured is when you have too high CC pressure, the oil is "blown around" more. Lower CC pressure the oil is blown around less. Either way can be detrimental in certain conditions. Could this be what happens when incorrect CC balance causes wetsumping?

The volume of oil below the windage tray, when level, I bet is less than half a quart. While engine running and more suspended & pushed towards back could be a little more. A whole quart in the sump would be a LOT while running. Just guesstimating. If you really want to know, while I have my jugs off I could dump a quart in there and see what that looks like (probably been done before though).

First,
I'd like to acknowledge this pic is from XLF member: meherdad_it.
I usually name the file by what it pertains to and the owner.

Second,
Quote:

Originally Posted by Tomcatt (Post 5768358)
I think that if the oil did what you show it would be picked up and pumped out by the scavenge pump and wouldn't be doing what you show.

At 6.000 rpm the surface speed of the crank wheels is ~200 mph. Think oil is going to sit as you picture it in proximity to the crank? Wet sumping kills power when it happens because the oil is whirling around WITH the crank wheels and isn't down at the scavenge pumps' pick up point getting pumped out.

+1

I'd buy part of the first pic at startup and intermittent times during riding conditions.
But you'll always have times when the sump has a lot less oil in it due to the bigger scavengers.
By the second pic, you've already started pulling oil up on the wheels and slinging it in a circular motion around them.
Oil just can't sit that close to the spinning wheels without getting blown around them.
That's another myth in my opinion of "the sump just floods with oil'.
Take a hand drill with a buffer or polisher (something of decent size and round) and turn it on high then lower it in a container of oil.
Before it actually sits down in the oil, it will start slinging oil.
Same concept in the crankcase just higher RPM and closed in space.

By the fifth pic, you've got a couple quarts in the sump.
All that oil right next to the sump port and the pump can't pic it up?

dieselvette 8th August 2019 02:13

Does anyone have GPM ratings for the pump supply, scavenge pre-07, and scavenge 07-up?

(How fast would you expect it to recover then, after all the slung oil settles back down to the bottom?)

Hippysmack 8th August 2019 02:17

Quote:

Originally Posted by dieselvette (Post 5768406)
Well, I think you and Hippy are both right, but how does it get to that point? I mean it makes total sense that the oil is flying around in there and NOT at the sump inlet, but what caused it to not get there? Was it accumulated in the bottom /front of the oil pan instead of the back? Why?

If there's too much air in the CC is it just so violent that everything flys everwhere but not to the sump? Or does wetsumping not happen at all at higher CC pressure unless other problem?

If there's too little air in the sump there is not enough draft to push the oil to the back?

Yes, it is violent in there.

The oil is flying around in there, it's also rising into suspension with the air and getting blown around, hitting things falling out of suspension back to the floor.

I think the disconnect is positive and negative pressures.
Normal scenario for scavenging:
Positive pressure (downstroke) is GOOD for scavenging.
PUSHES the oil to the sump port for pump pickup (detach that from puking oil).. this is normal.
Once it's to the sump port, the pump removes it.

Negative pressure (slight on upstroke) is not necessarily bad for scavenging since there is only so much oil in the sump to remove.
But it doesn't push the oil to the sump port as on downstroke.
This is also normal.

The pics you posted depict a never ending vacuum in the crankcase.
This is not consistent with the motion of the pistons.

Hippysmack 8th August 2019 02:26

Quote:

Originally Posted by dieselvette (Post 5768409)
Does anyone have GPM ratings for the pump supply, scavenge pre-07, and scavenge 07-up?

(How fast would you expect it to recover then, after all the slung oil settles back down to the bottom?)

I don't remember off hand.
I've seen something on the subject but testing needs to be done in a controlled environment including keeping viscosity at operating temp during testing.
That's on my list.
But I haven't seen anything I could lay money on.

Recover...
That's hard to explain.
The engine never recovers oil flow.
It's a constantly varying CC volume, constantly varying oil flow system.
Chaos IS normal. :)
This is the way it has been since the beginning of the Sportster line.

edit:
I guess you could call our engines a 'controlled chaos'. :smoke

bustert 8th August 2019 03:14

i doubt seriously you have more than a few ounces of oil in the trap. after a run, pull the never pull plug and drain it, even angling the machine for max effect.
i think there is corn-fusion with the terms positive and negative. the over-all effect below 5k is a net negative, never a transition to positive.
in electronics, you can have two negative voltages and yet one is more positive only because it is less negative. now i am corn-fused or is it the crown i am drinking.
if there were no blowby, then c/c pressure would remain constant after all, if nothing in, nothing to expell. that says a lot on how leaky these air cooled machines are.

bustert 8th August 2019 03:32

if i had dimensions, figuring volume is no biggie. no, i am not pulling my pump for that.

Hippysmack 8th August 2019 03:54

Yeah, it sounds like the crown.....

Tomcatt 8th August 2019 03:56

I still think that what's needed is an oil pressure relief. At higher revs it would work like "the bypass" but would maintain adequate flow at low(er) revs. Have we come full circle yet?

Or you could buy a set of S&S cases that have better oil management.


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