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

dieselvette 24th July 2019 06:36

Quote:

Originally Posted by bustert (Post 5764481)
first of all, do not need to do that, all i have to do is hook up my scan tool to the honda and pull the air cleaner off and watch short term fuel trends, THEY WILL CHANGE!
second of all, how does a filter work??? by impactation right???
if that is true, there has to be a resistance to flow and the media is like a labyrinth maze.
offshore, air intake is part of a preventive maintenance and was monitored via electronics and you could see the results and varied by rpm and load. when filters cost several hundred dollars, trust me, the oil company wants their money's worth. same with oil, at 70>80 dollars a pop and you have 7 large or 21 small units, it adds up so they monitor diff'l and run oil analysis and with the addition of spinners, they go well over a year on an oil change 24/7 run time.
i think we are on diff tangents.

Totally understand all that. But with a sporty the dyno says x-amount of filter area is enough for x-amount of hp (air pumped). So if the filter was a measurable restriction, the dyno would say it's taking HP away, get a bigger one. Some pressure drop, yes, but not enough to affect breathers.

dieselvette 24th July 2019 06:40

Hippy:
Vent your breathers to outdoors, and then try the oil cap scenarios.

Keeping in mind that maybe your umbrellas are intermittent, and that may throw off any data.

dieselvette 24th July 2019 06:51

Quote:

Originally Posted by Hippysmack (Post 5764277)
The first thing that happens on downstroke is that positive pressure (greater than atmosphere) is generated due to the restrictions of:
Case volume
Path to the vents
Vent hole size
Vent line (if applicable) length
Any induced air from the breather valve(s) not closing properly

To reword this - Only on the first stroke. After that, there are pulsations from atm to vac. Unless you have excess blowby, or air coming backwards through compromised umbrella valves.
Quote:

Originally Posted by Hippysmack (Post 5764277)
But ring blowby can also happen during upstroke depending on ring condition, thus oil entering the chambers.

How much "blowby" is this really? If your rings are that bad, need to fix it. Because during compression stroke the pressure above the piston is say 150-200psi, compared to lots more PSI during the power stroke. Any blowby that matters would occur during the power stroke.
Don't see how this would cause oil-burning anyway, that only happens during intake stroke - vacuum above piston, relatively more pressure under it (worse if your umbrella valves aren't sealing).
Quote:

Originally Posted by Hippysmack (Post 5764277)
Blowby adds to positive pressure which throws out the balance.

Yes, but blowby is easy to diagnose with a cylinder leak-down test. If it passes leakdown test, then most likely the rings are OK. Look for a breather problems, or valve guides/seals.
Quote:

Originally Posted by Hippysmack (Post 5764277)
The more the vacuum, even lower the positive will begin.
The rings act as a buffer between these two conditons as excess pressure could run both directions.
But positive pressure aides in oil scavenging.
So lowering positive pressure by default also hinders scavenging.
That's why racers with vacuum pumps use multistage scavenge pumps to account for the imbalance to scavenge and improve it.

Exacty, and racers like Aaron would describe that as an "art" to get perfect. The stock configuration is claimed adequate for any streetable bike, but upgrading to better-scavenging oil pump is highly recommended for 04-06 bikes. Keep in mind racers don't care if they use oil, as long as it's not robbing horsepower during the race. (They're not putting 1000's of miles on.)
Quote:

Originally Posted by Hippysmack (Post 5764277)
Same thing with lowering the oil level in the tank.
You are lowering the amount to be scavenged later which lowers the amount of oil that could get suspended to mist thus lowering the density of what does get suspended.

I don't think that's totally correct - I think the extra headspace is needed in the oil tank to keep all pressures and flows "in balance". Cam case is connected to this headspace (albeit by a 1/4" line) and perhaps this is more of a "vacuum reserve" that helps the crankcase be at higher pressure than the cam case during pulsations, thus better push for scavenging?

Getting really deep in the weeds here. There is really no need to reverse-engineer it just for the purpose of explaining those one or two outlier odd-ball scenarios. I'm willing to bet that many of the venting or wetsumping issues brought up throughout the years, could have been solved by addressing simple things. Except for being confused by all kinds of over-analyzing, which leads people down the wrong paths. Just need simple points like "the three most common causes" and people can ask questions from there, if needed.
Quote:

Originally Posted by Hippysmack (Post 5764277)
If you do test your oil tank pressure, could you take pics of the apparatus ?
That'd be helpful to others I'd think.
More data is needed in the form of testing data.
If you pull a vacuum on the tank with a mighty vac to test it, how much vacuum or how much is too much will it take to do a proper test?

Yes, I plan to do a tank leakdown test, so I'll get some pictures etc. That is a simple test that someone can do, to rule out the tank as a culprit.
Quote:

Originally Posted by Hippysmack (Post 5764277)
All tanks no matter of construction have puked oil from higher pressure with the cap on just like the breathers puke oil.
The oil level isn't getting higher but the pressure above it is.
This causes the pressure to break the seal of the cap or bust the tank and bring oil with it from below.
With the cap off, the pressure is relieved.

When they say "puke oil" I think it actually means that some splattered out, presumably along with air. A drop here and there can make a BIG mess. And the solution is to run the oil level not so full. And that leads to your next point...>
Quote:

Originally Posted by Hippysmack (Post 5764277)
Also with the cap off, you are connecting the entire pressure system including the crankcase and rocker boxes to atmosphere.
As far as air pressure is concerned, they are all as one.
You can't have more pressure in the rocker boxes than what's in the cam chest or crankcase.
The air has to back up from the source first and then reciprocate throughout the system.
That is why pulling the cap matters, the air throughout the bottom end including the top will react to the cap being off.

True they are all connected, but it's not static. The pressure below the pistons is cycling at an alarming rate. But for air to move takes time. At just 3000 RPM the pressure is changing 50x per second. So by the time you get to the end of the tank vent hose, there's very little movement. (As when Aaron connected a length of hose directly to the timing plug, nothing dramatic). But it could be a problem if the cap blew off due to high oil level, and make a person think breathers or too much blowby, but really they just had too much oil in the system.
Quote:

Originally Posted by Hippysmack (Post 5764277)
As cause and affect, if the tank is leaking, why wouldn't you also look into the breathing system?

You could, but this may be chasing ghosts. Air leak on oil tank can cause breathing problem, or in rare cases be caused by it. So fix the tank, and inspect other things.
Quote:

Originally Posted by Hippysmack (Post 5764277)
Same as weeping rocker box gaskets. Why wouldn't you add the breathing system into diagnosis with bad gaskets.

When replacing top end gaskets, advise replacing umbrella valves if there was any sign of breathing system problems. Or, even if not. They're cheap and easy to change. Inspect for other common breathing causes too.

Four Speed 24th July 2019 13:57

60Gunner, we are in agreement. The PCVs job is to cap crankcase pressure by allowing pressure pulses out not back in.
Your mod moves the breather to a better position away from heat where an elastomer valve should work more reliably.
And yes, I also see hardly any foaming in the oil tank after a ride. I hope your confirmatory observation will now convince
Hippysmack on that point.

Quote:

As when Aaron connected a length of hose directly to the timing plug, nothing dramatic
Good post dieselvette. Regarding this specific point, if that was just a hose then the air pulses will reach a point where you have
a standing wave. Introduce a decent one way valve and you get a steady draft out. That does affect scavenging and I suspect
will reduce wet sumping as there is less aeration of the oil in the tank as both myself and 60Gunner have found after adding PCV valves.

bustert 24th July 2019 14:37

running auto pcv
3 reasons not to
1. their design for the auto makes them unsuitable due to weight, inertia, cycle speed, pressure and flow range. this makes for soon to happen failure.
2. they were designed for multi-cylinder water cooled engines with wet sumps and over-all less significant air displacement. motorcycle engines have fewer cyl's and usually smaller dry sumps and air cooled and significantly more air movement. the only common thing is that they are otto-cycle engines
3. the auto pcv is designed for smooth changes in manifold intake vacuum and operate on a vacuum behind them. the motorcycle has a faster more aggressive pumping action with severe pressure oscillations. a valve designed for vacuum responds diff than one for high pressure. when we force air through it, we take it outside of its design.


the valve will not last and will leak, bringing back in air. how will you monitor that?? also of note, on an auto engine, the c/c has a secondary means of escape for the c/c vapors, the motorcycle does not. they will make considerable noise.

bustert 24th July 2019 14:46

leak down is a good test but is a static test. it is a good indicator however and points to where the leakage maybe but it is not all inclusive. a good example is a diesel engine, dynamic pressure testing reveals more info.
do you really need a vacuum under the rings??? desirable but really, a diff'l is all that is needed. as mentioned, industrial engines can be set for positive c/c pressures if needed. we are talking way more power than a mc engine.

60Gunner 24th July 2019 15:29

Quote:

Originally Posted by bustert (Post 5764753)
running auto pcv
3 reasons not to
1. their design for the auto makes them unsuitable due to weight, inertia, cycle speed, pressure and flow range. this makes for soon to happen failure.
2. they were designed for multi-cylinder water cooled engines with wet sumps and over-all less significant air displacement. motorcycle engines have fewer cyl's and usually smaller dry sumps and air cooled and significantly more air movement. the only common thing is that they are otto-cycle engines
3. the auto pcv is designed for smooth changes in manifold intake vacuum and operate on a vacuum behind them. the motorcycle has a faster more aggressive pumping action with severe pressure oscillations. a valve designed for vacuum responds diff than one for high pressure. when we force air through it, we take it outside of its design.


the valve will not last and will leak, bringing back in air. how will you monitor that?? also of note, on an auto engine, the c/c has a secondary means of escape for the c/c vapors, the motorcycle does not. they will make considerable noise.

The krankvent isn't a cheap auto pcv. It's specifically for motorcycles. More specifically Harley Davidson motorcycles I think. Probably why it cost $100+.

Cheap auto PCVs were tried. They didn't close fast enough.

I was just reading the back of the package and it does say:

"use a filter at the end as it's designed to let a small amount of air back in as the pistons go up to maintain the proper amount of vacuum in the crankcase at all times."

Must be an awful small amount as I couldn't detect it sucking my paper in.

Four Speed 24th July 2019 17:14

Quote:

use a filter at the end as it's designed to let a small amount of air back in as the pistons go up to maintain the proper amount of vacuum in the crankcase at all times.
Hmm. I suspect that is Hayden covering themselves about how quickly an injection moulded valve can close.
My ET can run without a filter but a well designed reed valve should have a bit less inertia than an umbrella valve.
Nevertheless, I still think the Hayden should be an improvement over standard HD umbrella valves and you are already
seeing the benefits in the oil tank. I am curious if you would see any benefit from changing to a reed valve. I suspect it
would be marginal and only at higher revs but the down side being more noise.

I also agree with Busterds comments about using an auto PCV but I may have confused things by using the term PCV.
60 Gunnner and I are both using valves designed for HDs.

60Gunner 24th July 2019 17:33

I was tempted to try this reed valve but the Hayden Krankvent had excellent reviews and all the usual places carry it. I'm happy with the results, it's quiet, and half the cost.

Folkie 24th July 2019 17:36

Quote:

Originally Posted by Four Speed (Post 5764775)
Hmm. I suspect that is Hayden covering themselves

https://image.ibb.co/dLCGBw/Agreed.gif

You don't maintain a vacuum by letting air in. :doh


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