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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (

Hippysmack 12th July 2019 07:41


Originally Posted by dieselvette (Post 5762079)
Basically I think the squirters have no ill effect, except during that time when the scavenging is getting behind...

Oil in suspension - should only increase with RPM (or does it?)

Any restriction does change flow.

My theory on the smaller holes is that they're "just big enough" (or a little more than that) to let air out fast enough when pressure rises, but small enough that air trying to come back IN (as the check valve closes) is not any significant volume.

Well, the squirters arrange for more oil to be in the sump at once on both upstroke and downstroke (from the feed pump).
They also decreased backpressure on the oil filter with the added outlet downstream.
But the pump will only give what oil it will give (positive displacement).
Feed volume (to the sump) is based on RPM, (restrictions already passed).
I probably shouldn't have used a water hose example as restriction does add flow.
But going further thinking (at the time) you can only get so much flow from a water hose.

I believe I agree with your explanation of the hole size during positive moments.
It gives to the fact that the balance has to be maintained.
However, during negative pressure, you used bigger holes as did Gunner with no ill affect on time of breather closure.
It's not outside air that closes the breather but rather inside differential.
The speed the breather closes depends on health / construction of the breather as pressure reverses.
Big hole / small hole when it reverses should have no affect on how much air is pulled in before it closes.
But a certain amount will get pulled in as pressure reverses (until the breather closes).
Either is minimal unless the breather isn't working properly.

One more thing to consider is that with 2 breathers (one on each head), the condition of EACH breather can be a factor.
(if one closes before the other)

The squirters added more responsibility to the scavenge side.
It has to keep up or else.
If it doesn't (due to triggers to hinder it), then the sump retains more oil sitting there waiting to be suspended.
They add 'some' extra oil in the sump even though they have small orifices.
Extra oil can mean higher oil density in suspension.
The higher the density (not volume) of the fluid (air / oil mix), the more it drags on the rotating parts it contacts.
Squirters add oil to the sump on upstroke and downstroke.
(and give potential for added oil suspension while gravity falling to the sump as all gravity oil can)
Head drains fall faster on upstroke (negative pressure-suspension process).
At the same time, squirters send oil up toward the pistons.
Some of that is sent into suspension also even at idle.
Goose the throttle at idle, get more oil from the squirters all of a sudden.

Of course, there are several triggers to hinder the oil pump.
Some rubbermounts puke at 55MPH.
I don't think that's RPM but rather a imbalance in the system somewhere.
That doesn't necessarily mean it's the breather though.

Most oil suspension happens on every upstroke regardless of RPM.
That's the splash oil we need for lubrication.
Downstroke lowers the volume between pistons and case bottom (positive pressure).
Upstroke pulls oil into suspension thru vacuum (negative pressure).
Oil in suspension may actually decrease on higher RPM.
The faster the motion from top to bottom of the pistons, the more equaled out positive and negative pressures become.
Thanks yoda. :D
Positive pressure doesn't have as much time to build or vent before the next upstroke.
Likewise negative pressure doesn't have as much time to pull oil into suspension before the next downstroke.

When you see oil puking out the breathers at high RPM, remember, CC pressure is more equalized then.
Or should be.
The big change at higher RPM is blowby.
This adds to positive pressures and throws out the balance.

edit:Another change would be how fast the breather (umbrella) can close at higher RPM.

Changing to 1250 shouldn't change the balance (all things equal).
It may just make a stronger bond between positive and negative pressure.
(higher controlled windage)
So it may take a stronger force to change the balance.
The bigger bolt holes may not change enough to matter.

Hippysmack 12th July 2019 08:09

How does oil migrate back through the bearings.

harley506d 12th July 2019 09:09

Did the plug cap mod myself, a nice cheap and cheerful kind of thing.
That's pretty clean.
I assume stock air cleaner goes over the lines OK?

I cut the spigots off, leaving about 1/16-1/8". The remaining stubs will (maybe) press on the rubber plug caps.

Hippysmack 12th July 2019 17:46


Originally Posted by harley506d (Post 5762087)
Did the plug cap mod myself, a nice cheap and cheerful kind of thing.
That's pretty clean.
I assume stock air cleaner goes over the lines OK?

I cut the spigots off, leaving about 1/16-1/8". The remaining stubs will (maybe) press on the rubber plug caps.

Stock 1200 and stock breather bolts?

harley506d 12th July 2019 19:24


Originally Posted by Hippysmack (Post 5762131)
Stock 1200 and stock breather bolts?

Yep, totally stock motor and filter. The airbox only has the restrictor removed.
I fitted new breather bolts without the o rings.

Now and again i remove the pipe that loops to the breather filter to check for any oil.
never found any, only a tiny drop of water one time.

Hippysmack 12th July 2019 20:00

Well that definitely adds to the suspense.
Where is your vent line end placed, high or low?

60Gunner 12th July 2019 20:09

I'd be hardpressed to find anything that IS stock anymore.

Hippysmack 12th July 2019 20:31


Originally Posted by 60Gunner (Post 5762150)
I'd be hardpressed to find anything that IS stock anymore.

You got that right! :)

harley506d 12th July 2019 22:12

Had to search for pic! Filter just tie-wrapped to underneath airbox. I suppose the motor is not really "stock" as i have done the jetting etc. But having totally screwed up my beloved 1340 FXRT years ago , i am leaving this alone! Gives me 50+U.S. mpg, and goes to 100mph easily enough, (stock exhaust at the moment) it's good enough for me!

Hippysmack 12th July 2019 23:53

That looks nice and tidy.
I have a question about the bend in the line before the filter.
What, if at all, have you noticed in the line at that bend?

I'm thinking oil / condensation could settle there even if it doesn't run up to the filter.
I guess better put, ever pulled the filter to inspect the line near the bend?

I like the 'Y' down low instead of the horseshoe up with only one side running down for the same reason.

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