The Sportster and Buell Motorcycle Forum - The XLFORUM®

The Sportster and Buell Motorcycle Forum - The XLFORUM® (
-   Sportster Motorcycle - Bottom End (
-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (

Hippysmack 28th July 2019 20:28

Me thinks we've created a munster..:wonderlan

60Gunner 29th July 2019 16:29

I've tried to find any negative impact of moving the breathing and using the krankvent. There are none.
Temps are better than ever and so is scavenging.
If the stock setup is good enough for you, then by all means keep it. If you're trying to find a reason stock is better, you won't convince anyone that's done this. No one I'm aware of has ever gone back. I tried to find a reason to.

Hippysmack 29th July 2019 16:45

Go back through this thread.
I am not trying to prove any way is better or worse than the other.
I'll leave that to you and others.
I'm just gathering information about the title subjects (not just either way of venting).
There are way too many opinions that sway people based on someone's experience.
But there are many more considerations than just moving the vent location that are usually looked over.
Because a racer said so is no reason to go and re-engineer your entire street engine.
That seems to be a going trend (not speaking of you).

I may be the only one here that is trying to get a overall just of the entire system, not just the breathing system.

Just like you have to crack a few eggs to make an omelet, you have to refute some opinions to get to the guts of a subject.
That's when things get complicated as 'my opinion or my mod' is all you have to do and all your troubles go away.
History has proven that just ain't so.
I'm laying out subject matter that makes me go hhhhmmmm.
If what I'm presenting doesn't agree with anyone, I'm completely open to discussion.
I've already challenged some of my own opinions based off posts in this thread.
Discussion is a good thing. It helps us all learn more.

That's the purpose of this forum.
But refuting any other way of doing something hinders the learning process of all concerned.

bustert 29th July 2019 17:06

ye who stirs the pot last usually get the blame for how it tastes!

i like your diamond view of things. many facets to the total cut so who's to say this side looks better, turn it in the light, does it not change??
no, have not forgotten about the slack tube, been out of town and have two steels to put together.
i am going to pull the timing plug and make an adapter.

Hippysmack 29th July 2019 17:08


Originally Posted by bustert (Post 5766148)
i am going to pull the timing plug and make an adapter.

Sounds good bustert.

Highly-Dangerous 29th July 2019 19:32


Originally Posted by Hippysmack (Post 5765831)
Harley Davidson Motor Company. :D

Thank you!!! :D

Four Speed 29th July 2019 21:10

Bustert somewhere on here I saw an impressive Iron Head that had one of these reed valves mounted on hose from the timing plug and then to a catch tank:

60Gunner 29th July 2019 21:26

I'm trying to find a reason one way works better than the other myself. A reason why it was moved to the heads from an engineering standpoint. I'd switch back in a heartbeat if there's one good reason to. Im playing the side of cam chest because other than 4 speed, no one else is really providing any info on how it works.
It's been suggested the stock breathers let a certain amount of air back in to keep pressure enough to help oil return. I think that's bs. Oil will drain just as well at atmosphere or even a slight vacuum. Maybe better. A clear cover would be nice. All I can say is my head temps seem to have gone down but I made several changes that could be part of the reason so it's hard to say how much is because of location or the better valve when compared to the failed stock ones. The fact I even had failing stock ones is an issue itself. Letting air in, any air, is not a good thing imo.

As for the krankvent imo it's already proven to be a better one way valve than the stock ones. Has anyone ever had one fail or need replacing? Idk but I highly doubt it. Does it close faster allowing less or no air back in? I think that's been shown. Perhaps not scientifically enough but it definitely works better at what it's supposed to do. Then there's the warping issue of the stock ones. I thought maybe they had been improved on since 04 but apparently not. Too bad. They could use improvement. Not sure where I saw metal ones that came apart.
Nevermind about the cosmetic aspect about the location. Perhaps some people like the dangling hoses. Who am I to pee in their oatmeal? ;p
Maybe pulling rocker covers to service or replace them is is an acceptable past time. Just not a favorite of mine. If I never had to pull them again it wouldn't hurt my feelings. I am once the riding season ends, however. Wedge is teaching me the finer points of home porting. Picked up a nice little angle grinder with bits I need at an estate sale down the street 2 weeks ago in fact.

I don't know what more can be done to prove or show one location is better than the other. At least not from a standpoint that matters much.
As a side note, it looks like I'm pulling that fitting. Turns out I have a chrome one. Found it digging thru my stuff. I think it came with my speedo housing setup. Had a few electrical connectors packaged with it and a couple hose clamps. Go figure.

Four Speed 29th July 2019 21:43


Temps are better than ever and so is scavenging.
That is my conclusion as well 60Gunner. What seems unresolved is the claim on here that more crankcase compression assists scavenging;
I contend that it just increases aeration. Like you, I also see more oil in my oil tank after I fitted a proprietary one way valve.


A reason why it was moved to the heads from an engineering standpoint.
I strongly suspect the mods HD did before the incoming Euro 2 etc emissions standards to reduce crankcase breathing were not to do with
performance but to keep hydrocarbon emissions to a minimum, as reflected by the decline in claimed power output. At the time Hydrocarbon
emission were cut back significantly, so recirculating the breathing inside the lubrication system would doubtless have helped but maybe this
lead to the subsequent increase in oil pump scavenging capacity.

Hippysmack 29th July 2019 23:53


Originally Posted by Four Speed (Post 5766229)
What seems unresolved is the claim on here that more crankcase compression assists scavenging;

Crankcase pressure is ever changing on a running engine.
The whole variable crankcase pressure issue.

To quote exact wording from the FSMs:
2004 Hd FSM, page 3-11,
1998 HD FSM page 3-29,
1986-1990 HD FSM page 3-7,
1979-1985 HD FSM page 3-7:
Oil flow to the pump is accomplished by the scavenging affect of the pump and by the pressure created by the downstroke of the pistons .

So we know downstroke (positive pressure) is a normal productive part of the scavenging system.
The good books tell us so.
Hammer Performance also suggests a vacuum on the system hurts scavenging.
We've seen the balloon test that shows during idle and normal riding, in/out pressure is relatively stable up to 3500 RPM ish per DK Custom.
(variables unknown of course)

What am I missing?
The extra blowby shouldn't be present until you hit the high speed / high RPM.
That's the extra air pressure that adds to positive on downstroke.
But an engine can wet sump due to quick on/offs as well.
Quickly adds more oil to the sump and then the off throttle doesn't allow as fast of scavenge with the quick reverse affect of CC pressure.

Try the balloon test and tell us how your engine reacts.
I can't on mine until I run vent lines.
So far I've kind of been on defense trying to learn of what you've been saying.
But now that I'm more up to speed, I can't understand your reasoning.
It was presented in the wet sumping thread that higher crankcase pressure aides in scavenging but it hinders crankcase pressure as it picks up more oil in suspension as well.
It makes the air/oil mist thicker.
Everything, including Hammer Perf, suggests the thicker air/oil mist is what overcomes the breather valve to puke oil out the vent
There is nothing to suggest, other than what you've been saying, that higher crankcase pressure makes scavenge oil more bubbly.
So I ask, where did you get that information from?
If you'll cite it, I'll research it.
There are several conditions as to what happens to make aeration in the oil scavenge return.
The main reason is that the oil pump scavenge gerotors are bigger than the feed gerotors.
Doing the math, aeration is most prevalent due to the oil pump scavenge side working too good.
Doesn't that make sense?
I've read from IHs to Evos, all year gerotor pumps that the oil, when viewing inside the oil tank, will return and then not return and that should be the cycle by default of the math.

During the time that the oil pump has just pumped what was available at the scavenge port and is waiting for downstroke to deliver more oil to the port, higher crankcase pressure is wanted to deliver that oil.
If there is only a slight push pull going on, the pump could cavitate due to no oil to the inlet especially during several quick on/off throttles where CC pressure is the most turbulent and can pick up the most oil during this time.

All times are GMT +1. The time now is 06:16.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
XL Forum® - Linson Media LLC