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  #121  
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Quote:
Originally Posted by Hippysmack View Post
What does that spring do and is the probe sticking down into the tank hollow?
Makes me wonder if the O-ring seal has something to do with rubbermount heat and oil consumption.

OEM cap like the one pictured - no - the end is sealed, the entire gray piece is one mold, as long as the main oring is good you're OK, and that's all you need to cap the tank. The rest is just there to make it fancy.

The O-ring not sealing - seems like it would take a heckuva leak though (like maybe NO oring at all) to cause a noticeable issue. NEED to read Aaron's experiment with the Buell. I found it here:
http://xlforum.net/forums/showpost.p...5&postcount=34

Similar it is, to your removing the cap at idle. You've just opened a 1/4" 3-ft hose from cam chest to atmosphere. Differences you were at idle, and connected to cams not crankcase. It's a moot point tho, because if you suspect oil tank/cap leak you wouldn't diagnose it by looking at your venting system. It is easy to do a tank leakdown test with a mity-vac (or something) on the vent line - if tank is sealed, it's sealed; if not, then find the leak and fix it. After testing/fixing that and you still suspect venting issues, forget the tank and carry on with other checks.


It doesn't, I'm looking for reasons why it doesn't.
Then reasons why Deimus's first mod didn't work (PCV on oil tank vent) and consequently why other folks that did that mod where it did work (somewhat).

I still don't follow. The tank can't puke oil out because the oil level is *inches* down from the top. The only way to get it to puke would be wet sump, add oil, then wet-sump again, and add more, then maybe after the sump empties it would be full enough to come out the top. But that's because there's way too much in the system. This new "venting problem" would NOT have started due to a venting problem. To say that is mis-diagnosis (which I'm sure some have made that mistake).

To quote from aswracing post linked above "Excessive airflow & oil discharge through the breathers can be caused by malfunctioning umbrella valves that are allowing air into the motor." I think this would apply to any venting mod with an inadequate check valve. A regular PCV valve doesn't work well enough as a check valve.

Agreed, the extra air intake is harder on piston downstroke.
But why is it even harder when the oil is hot?
Operating temps give clues to conditions that end up being bad for the engine.

By air compressor, I mean UNDER the pistons. What happens at the intake & combustion chamber, stays there (mostly).

Hot oil is a symptom, not a cause. It's confusing because bike also runs different when oil is hot - but that's not relevant, just need to find what made it hot.

The oil gets hot because of a)hot weather, slow traffic + high revs; b) lean running conditions; c) wet-sumping.
Any of these are easy to detect.
Venting = not a factor


There is a balance I'm looking for that has to be maintained.
I need data for a more complete understanding.

Don't need more data, already confused. Just need to compile it. Keep it as separate topics, even if one can cause the other:
-Wet-sumping
-CC venting

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2004 1200 Roadster Custom-Electra-Glide-Sport-Touring-Edition
SE air cleaner w/venting routed outside a/c
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Stock CV carb w/ Yost tube + DS idle mixture screw
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  #122  
Old 18 Hours Ago
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while that is true, that the air cleaner MUST flow more than the cfm of the engine needs, the media does in fact effect air flow. of more importance is how or the direction the flow must take. the best is a direct inline flow which does not happen with an hd ham can. if you introduce angles, they must be wide radius and the ducting of correct size as every curve or turn adds resistance and more importantly turbulence, best to have laminar flow.
my vents are not stock and probably flow more.
when the the vent exists the orifice, as mr. hippy mentioned, the velocity must increase but after the orifice the pressure must drop and drops greater as distance increases. when this vent hits the volume of the can, it becomes lazy and more so with little throttle demands at idle. now what happens when you get lazy flow, well anything in suspension will coalesce and drop out. this leads to oily/water mix. now is the really a vent issue, hummmm, well maybe and maybe not, i am more inclined to believe it is an engine condition issue since it progresses with age.
as an example, ever fooled with pontiac engines with trip-duce?
really could be anything but this is a personal example.
if the carbs are syn to open in one felled swoop, on a take off, the air flow becomes near atmospheric for a brief moment, the fuel drops to the manifold floor, this results in the two inside cyls on both banks to run rich and the further cyls to run lean. an ole trick was to groove the manifold floor so that any drop out was directed to the leaner cyls.
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  #123  
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Quote:
Originally Posted by aswracing View Post

First, a little background. In the stock configuration, the crankcase vents through a pair of "umbrella" valves, which are essentially check valves. There is no air inlet into the motor. As I understand it, the idea is that as the pistons come down the first time and the crankcase air is expelled, the air is forced out through the umbrella valves. But when the pistons go back up, the umbrella valves block the inflow of air, causing a slight vacuum in the crankcase. The next time the pistons come down, crankcase pressure will return to atmospheric. If no air is allowed into the motor, the crankcase will cycle between a vacuum (pistons up) and atmospheric (pistons down).
I read that post, not the whole thread yet, but:

I agree as I mentioned earlier, that the crankcase is at atmosphere while not running.
And a slight vacuum is pulled while running.
Then a push - pull is established while running.

But 'the next time the pistons come down, crankcase pressure will return to atmospheric."
Inbetween that you get this:
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

These things will bring the pressure inside to higher than atmosphere, else there would be nothing to expell.
As the air is pushed out of the vent, at BDC, the air returns to atmosheric. Check.
That is the problematic condition, the higher pressure before returning to atmosphere.

The negative (vacuum) on upstroke I'd think is more stable than the positive pressure on downstroke due to ring blowby and others.
But ring blowby can also happen during upstroke depending on ring condition, thus oil entering the chambers.
Blowby adds to positive pressure which throws out the balance.
Let's use X (+1) as positve and Y (-1) as negative.
In a pefect world, X goes down and Y comes up ------ X+Y=0
Add ring blowby and you get ------ X+1>Y------ or the real result. Balance is off by nature of the moving parts.
The pistons move up and down almost together.
That makes the push/pull environment more violent.
Add a vacuum pump with Z (-1) amount of pull:
Now you get X+1=Y-Z... seems the balance (to zero) is restored even though positive pressure is compiled of blowby.
But the lower the negative pressure is at the beginning of the downstroke, the lower the positive pressure will be.
If you are generating 2 psi of positive pressure on downstroke but reduce it's beginning surge to -1 psi (Z), the result will be only 1 psi of positive pressure during downstroke.
-1 (+) + 2 equals +1.
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.

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.
Lower density of suspended oil drags the wheels less being lighter as it moves.

I've read posts where there was a concern with the plastic tank neck warping which would change the seal condtion of the O-ring.
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?
That depends on what the engine would pull at max volume... which is ?? volume.

I'm broke right now but I want to do some flow testing on the breathing system when I can so I can examine real data instead of figures out my arse.

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.

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.

As cause and affect, if the tank is leaking, why wouldn't you also look into the breathing system?
Same as weeping rocker box gaskets. Why wouldn't you add the breathing system into diagnosis with bad gaskets.
I think it's the big picture not being diagnosed is what I'm getting at.
Hence, I agree with carrying on to other tests.

Too hot oil is a symptom but it can also cause other problems as in less residual lubrication and damage thereof to pistons, lifters, bearings etc.
As I mentioned, it can also cause more oil to be suspended, drag the wheels (less power), overpower the breathers (oil puking) etc.
Sometimes it's not as easily detectable before it does damage to an extent either.
I do have these as separate articles in the Sportsterpedia but have brought wetsumping into the CC pressure article as it relates.
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  #124  
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there are cheap digital pressure recorders out there.
with the right orifice, a water manometer could be used, they use this methods on diesels to determine blowby and engine wear.
i do not think the hd engine achieves a negative pressure.
even if you tested this in alabama, it will not hold true every where. the elevation and barometric will have its nasty hand into the pie.
in a recip aircraft, the breathers pretty much remain an open system..
the little mention of auto pcv is not a very good idea for at least 3 reasons.
i have a couple of slack tubes and if i get time, i will do a garage test. this also is moot since everything changes with throttle opening.
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  #125  
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If you think about it without a negative pressure on upstroke, even if slight, the umbrella will not close.
It's not a seal from atmosphere without suction on the inside.
I can see negative building as the piston rises since the positive went out the vent.
Too much ring gap could alter that though.
Some pressure escaping the rings on upstroke to sort of equalize somewhat I'd buy.

I agree if tested here, the results won't be the same everywhere depending on elevation.
But that may be able to be calculated out later?

I tried again today with the cap.
Oil temp 210, raised idle to 1200 and lost 700 RPM.
So it's a variable figure.
I got the same figure when just cracking the cap open as with full off.

edit:
I forgot to mention I pulled the cap just after the idle was sufficient to take the enrichment knob back in.
Absolutely no affect on RPM.
So there is a correlation to the heat of the oil.

Last edited by Hippysmack; 7 Hours Ago at 04:02..
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  #126  
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Quote:
Originally Posted by bustert View Post
there are cheap digital pressure recorders out there.
with the right orifice, a water manometer could be used, they use this methods on diesels to determine blowby and engine wear.
Just hook up a balance tube to the back of your a/c, and fire it up, rev to full RPM and you will see how restrictive your a/c filter is at full flow. Compare that to the crankcase pressure variations and see that this is of little significance. If your a/c is significantly restrictive, get a new filter.

Yes things drop out of vapor or coalesce with pressure/flow changes, but I think that once anything is past the umbrella valve it doesn't matter anymore whether it presents itself as droplets or vapor, there's very little of anything unless you have parts somewhere in the engine not working right.

You are correct that a/c design matters for flow & HP, but only at higher RPM (flowrate). And then the only filter determines pressure drop, not the backplate design. Backplate design affects how "smoothly" the air enters the carb.
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