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Old 27th October 2019
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Hippysmack Hippysmack is offline
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I tried to bring it over here to begin with.
We may have scared the op away.
I don't know how the mods would take double postings but I can try to post them here maybe as 1 post. It'll be pretty long though.
This is one of those cases of asking forgiveness since I didn't ask permission.
I sent a msg to cantolina letting him know.

Originally Posted by Hippysmack View Post
These are some good bookmarks on breather mods and CC pressure in the XLForum's Sportsterpedia:

Breather / Venting Mods

Evo Crankcase Pressure and Engine Breathing:
Originally Posted by bustert View Post
dk customs numbers in your sportsterpedia link.
some interesting theory but in actuality it is slightly diff.
interesting numbers on vent cfm, which suggest something else is going on which supports the manometer numbers.
Originally Posted by Hippysmack View Post
Yeah there is gonna be some variance.
I've seen the balloon test and Aaron's breather dyno results but I guess your slack tube testing hit home the best for me.
But they all support each other basically.

I knew there was a point at which positive pressure would be greater.
And I assumed that would be around 5000 RPM.

But based on what I've read, I assumed pressure would be more to the 'slight' vacuum' side until that point.
Your testing shows it to be a gradual change in pressure as the RPM rises.
This shows just how pressure can change with the addition of air leaks and failed breather valves... and my removing the oil cap.
Originally Posted by bustert View Post
just using the numbers, it is a useful tool to determine top end wear.
for grins and giggles, take the sportster at .125cfm that being in good shape but later testing revels higher numbers, aka more blow-by and wear.
as per previous threads, the engine really does not have positive/negative swings, it goes by law of averages which the manometer shows. yes, down stroke does help oil circulation but the pressure diff'l is still constant.
in reality, the 1200cc engine has way more volume than that because you have to factor in the entire case enclosure.
the small amount of down stroke movement (the part that helps oil flow) is recovered on upstroke. the newer designs are more open than in the past which makes the law of averages more pronounced. the newer "u-tube" vs trap are less restrictive to oil flow also.
without consideration of orifice restrictions and just the numbers:
1cu/ft = 28,317cc
28,317cc / 1200cc (just using cyl displacement as example) = 23.6cc per stroke
if you factor in increase volume and restriction, the number will be lower.
of interest is the coast down number is the same which indicates that the slippage past the rings is consistent even though no combustion pressure. this slippage amount would be what is to be expelled. as rpm rises so does slippage and when it passes what the vent can handle, pressure rises, but one has to factor in time since there is less time for things to work.
so the point is, basically constant pressure and yes, vacuum is a pressure.

Originally Posted by Hippysmack View Post
Just like a compression test, you'll always have a certain amount of leakage into the bottom thru the rings.
And yes it is interesting that it is so consistent.

I don't feel like the DK test was awful scientific but just another tool.
I am not quite understanding the 'no combustion' though.
They wrote chopping the throttle to 0% with the clutch pulled.
But that was to let the engine decel on it's own while still running is what I gathered "on throttle let-off" even though they used the word chop.
So there was combustion at the time it seems.

The time doesn't show up in your tests?
I would think increased positive while the negative is lowered would also include stroke timing with increased RPM.
All one big stew.

Any luck finding a breather valve?

buster, if you wouldn't mind, I'd like to continue this conversation in the CC pressure thread.
Originally Posted by bustert View Post
according to your sportsterpedia, the numbers are consistent across the board from idle to cruise to hard accel to coast down.
rings float so it takes pressure to force them to seal.
even combustion pressure is subject to law of averages even though most only look at peak numbers.
when testing diesel engines, you are looking at law of averages which is way lower than peak pressure. now if you would use a more modern electronic recorder, you could plot the entire range but the old mechanical gauge set which is snub to reduce oscillation shows average numbers and you judge by this and mfg's data.
on the coast down, they did make it more consistent with idle speed, no load via clutch pulled in. but idle pressure is way diff than loaded engine. this test makes no since because the idle test is the same, maybe the numbers would be diff if the engine was in a true coast down.
Originally Posted by bustert View Post
i wonder about the terminology???
clutch in as in engaged
clutch out as in disengaged
perhaps you could get some clarification as this would shed some light on the above, does not make sense as surely they would know the test would be the same.
Originally Posted by Hippysmack View Post
Recreate this in your head:

In this test, air was captured and measured as to how much water volume was displaced in a fixed period of time.
Taking the liquid ounce displacement, you can convert that to Cubic Feet Per Minute (CFM) There are 957.50649350649 U.S. fluid oz. in 1 Cubic Foot.
Sportsters move the least amount of air through the breathers. Twin Cams move the most amount of air through the breathers, with little difference between air cooled and Twin Cooled.
Milwaukee-Eights move more air than Sportsters, but little more than half as much as the Twin Cams through the breathers.
Even more surprising is the least amount of air is moved on all bikes while at cruising RPM.
The only way to get a significant amount of air to move through the Sportsters was to get the RPM up around redline.
(and that crankcase pressure was probably because the valves were beginning to float) The most amount of air is moved through the breathers at idle, during hard acceleration and during deceleration.

The criteria for both DKs and Aaron's testing wasn't to answer some of the questions we've had.
DK's criteria was 'how much air was passed out the breather vents at idle, under a load, at cruising speeds and on throttle let-off' for different model engines.
So there main concern was how much air moved out of the engine.
Your testing backs up their data showing at most of the RPM range, there is more vacuum than positive pressure.
And it's the positive that leaves the engine. Therefore, their results are equaled out more.
Even though there is normal blowby throughout the RPM range, the vacuum created buffers that.
We've read and heard the phrase 'slight vacuum' from many sources.
But your slack tubes put a visual to the process showing that the 'slight vacuum' is not really a stagnant number but a moving range.

15 inches of vacuum that all of a sudden is hit by 5 inches of positive pressure rolling the throttle still yields 10 inches of vacuum at the time.
So there would be no air moving into the balloon or container at that point.

Aaron's testing was with the normal breather vents (with and without the timing hole plug removed) in the interest of measuring whether either would increase HP.

In theory and during that transition from 15" to 10" vacuum, more oil is pushed toward the scavenge hole in the sump, the pump gets a fatter supply of oil to send to the tank, pressure goes up in the air space in the tank due to the restriction size of the vent.

Aaron said "necking the timing hole down to a 3/8“ hole and connecting 2 feet of hose adds a pretty significant restriction.
The vent hose from the tank to the cam chest is also a restriction as more air/oil is forced into the tank but the vent restriction remains the same.

That's why I was wondering about your testing from the oil tank showing the pressure equaling faster than in the crankcase.
That would suggest the tank is being overloaded before oil pukes out the A/C.

Originally Posted by bustert View Post
i wonder about the terminology???
clutch in as in engaged
clutch out as in disengaged
Technically, yes.
But normally 'clutch in' would be referring to the clutch lever as in 'pulled in' I believe.
Originally Posted by bustert View Post
i assume you are talking about umbrella float.
if you view this as a closed system, what only can escape is what sneaks past the piston assuming leak past crank seals are too small to be of any significance.
assuming once again the numbers only, the blowby is pretty much consistent at .0626 or .0125 from the pedia.
while there is a slight transition to positive it occurs only near the peak value where it is high enough to overcome umbrella/atmospheric pressures.
for grins and giggles, this would occur in the last 20% of the cycle and the law of averages controls 80%. the basic over-all pressure is negative. the newer designs are more u-tube and open ended at that so it does not take much to move the oil.
the bag has restriction and it has to rely on the umbrella and it is of smaller volume so the readings will be diff.
the only way to tell would to put a data logger on the machine and run it through the paces.
as a side note, all the oil has to do is get to the pump, past that, no longer needs any assistance as the pump takes over. also is that with the u-tube, rising oil level in the flywheel compartment would just spill over, by gravity, perhaps hd way of controlling oil pooling at high speed.
Originally Posted by Hippysmack View Post
This my gatherings on 'extra' air.

Ring flutter around 5000 RPM and higher is thought of as the main culprit on a healthy engine.
Gasket / air leaks react the same as ring flutter but at a lower RPM.
They allow more air into the engine that add to the positive and take away some of the negative (vacuum).
So the introduction of air leaks into the crankcase lowers the RPM at which pressure changes affect the system.
Worn / stiff breather valves that do not fully close will allow more air at atmosphere into the crankcase.
This lowers the vacuum and contributes to higher positive pressure on downstroke changing the ratio at a lower RPM.

assuming once again the numbers only, the blowby is pretty much consistent at .0626 or .0125 from the pedia.

That's why I believe stroke timing has it's say in the midrange.
Couple working pressure with the increasing speed of the pistons which helps to equalize positive and negative pressure during operation.
As engine speed increases, there is not as much time to build vacuum on upstroke or positive pressure on downstroke due to the faster changing piston positions.
Just as you can inhale air slowly and fill up your lungs but faster breathing will not allow you to fill them due to the faster time that you exhale.
This would make for a shorter range of (both vacuum and positive) pressure that would be able to build in the crankcase.
So the internal pressure is more stable until extra air (blowby from ring flutter or other) is induced into the crankcase.
But stability doesn't help scavenging as much as pulsations do.
So there may be more oil pooling when the pressure is stable which contributes to higher windage and positive pressure during that time.

I wouldn't imagine it would pool up to the shaft though without other issues beginning.

There would be massive wheel drag before then.

Least not forget about the timing of the breather valve closing.
Guess we could call that umbrella flutter. The faster it closes, the more vacuum is kept in the crankcase.
The slower it closes, the more air is allowed to lower residual vacuum.
Originally Posted by bustert View Post
if this is true, hd designed the engine wrong and all would be doing it.
bit busy at the moment putting up metal on my extra shop but will jump back later.
also of note, this is not consistent data between engines with diff hours run time so it does not hold water (actually gas).
the sportster engine can easily take 8k so banging out at 5k does not make sense.
will be back.
Originally Posted by Hippysmack View Post
Don't get me wrong, I'm not saying it's dead at 5000.
But there does seem to be a pattern emerging.
This is Aaron's breather vent testing.
Around 5700? there is a dip in HP.
It does pick back but rises slower after that. Of course there are lots of factors in that though.
That dip is a sliding figure also.

At the point, there is more blowby and you should be getting better scavenging.
And as long as the breather valve is up to par, you shouldn't have excess oil in suspension.
But higher windage can pick up oil faster. Again, it's all a balance.

This where he tested different breather valves.

But for those of us that live between 4000-5000, we can end up with sustained time around that dip.
Originally Posted by bustert View Post
first on the subject of so called ring flutter.
there are two type and a good engineering design is the first weapon to prevent it, the very reason i believe this issue is not that. the history of the hd design does not support that.
as far as dyno runs, you can run ten and get diff results and dips and twist are common and not always accountable to a certain mode of operation. it is a good tool but i have seen "seat of the pants guys" smoke the so called dyno tuned engines.
this type usually begins at the ring gap and mostly at medium load and high rpm. this would fall into the cruise range but then again, who cruises at high rpm (guilty as charged) and it would tend to rule out hard acceleration since engine demand is high, so it is a crap shoot. on this point, even "IF" you attribute the so called dip in the graph, probably WILL not be there on the road, toooo many variables!
this ring movement refers to the lifting of the piston ring off the bottom flank contact area and as i said begins at the gap as it is the weak link (spacing). this allows motion of the ring ends which in turn sets up a wave pattern that gets transferred to the entire ring, sorta like throwing a rock into the water.
engineering with low ring heights and more pressure on the gap area has a tendency to reduce this flutter.
past engineering, what elese to consider?
1. excessive ring height clearance
2. loss of ring tension which compounds gap loss of pressure, of note: diff ring shapes play a factor
3. mechanical contact (head strike)
4. fuel burn issues, aka, knock and such
5. worn out piston land grooves
6. groove base gas volume too low due to build up behind the rings.

i am going to break this up so as to be readable.

excessive increase of gas pressure on the ring sliding surface during combustion. this disturbs the balance of forces briefly and forces the ring to lift off the sliding surface (ring to wall). when this happens, the ring can no longer seal and the constant repetition leads to ring fluttering.
1. worn rings (loss of pressure force between ring and wall and ring stiffness)
2. out of true bore which allows ingress of combustion pressure into gap and ring to wall
3. asymmetric piston wear from bent connecting rods. the ring will follow a slight oval travel path due to being out of plumb. this oval pathway allows combustion pressure to enter the top ring land, piston ring and cyl wall on the side with less contact.
4. excessive, crowned wear on the sliding surface of the piston ring due to excessive height clearance.
5. damaged ring edges due to incorrect honing. ( the ring is torn open and frayed on the ring edges, more pronounced on cast rings without coating). gas pressure enters and lifts the ring off the wall.

the straw and "BB" rule.

if i take a straw and shove bb's through one end, eventually they will exit the other end. the hd when started is like shoving bb's into the straw and eventually a point is reached, bb in/bb out. it can only vent what comes in, it is a closed system unlike a car engine.
when you exceed a car's pcv system, what happens?? well, it backs up through the c/c air inlet usually plumbed to the air cleaner, not counting newer systems.
what happens when the hd vent is exceeded?? remember it is closed!!
for grins and giggles, say a stroke produces 24cc of vent, now multiply by rpm. now calculate orifice capacity and subtract the diff, the given rpm where it is exceeded will be the tipping point for a transition to a positive pressure. we know this is a scaled process, sorta creeps up on ya!
the umbrella is not an on/off switch, in fact, it might not even reach full open. with the law of averages, the negative and positive balance out and the victory goes to the strongest and can last the longest, aka, vacuum wins. this is what you are seeing via the manometer.
another point of interest is volume, the ratio between piston up and piston down. for grins and giggles let us same piston up and piston down are equal, this equates to a 2:1 ratio.
for grins and giggles, take two bicycle air pumps, one 2" dia and the other 3" dia, but both having the same stroke. which one will achieve highest pressure per timeline frame?
so the big "?" is can oil flow with negative pressures, why sure, all that is needed is a diff'l. also of note, a negative pressure also reduces aeration oil the oil.
how you say, well, pressure has a tendency to make the bubbles smaller, aka less surface area to interact with fellow bubbles. now with reduced pressure, the bubbles expand and surface area increases which allow more interaction with fellow bubbles which then has the effect of joining the two. if you ever scuba dived, and look up, you can see this in action.
Originally Posted by Hippysmack View Post
There have been many engineering changes over the years to combat wetsumping and ring seal. Check.
There is an article from the MoCo somewhere around the house, can't find it right now, regarding ring flutter from the IH days.

But Evos also battle excess blowby at high RPM. That's how gapless rings came about.
Then they found gapless rings sealed pretty good but weren't very helpful for scavenging (less blowby - positive pressure) in the mix.
So the problem hasn't been engineered away.
It may be better but it's also important to note that the these tests were performed on healthy engines.
Adding to your list, results will vary depending on compression ratio, piston size, health of the oil pump and a host of differences including varying degrees of wear as you mentioned.

Undoubtedly, Aaron spent some time on this.
According to him, the variable breathing methods tested were within the repeatability of the measurement.
And again, he was just looking HP changes.

10 best pulls from the stock configuration.

10 best pulls from timing plug vent configuration.

Just sharing what I've learned Buster, the only thing I'm really good at is tearing stuff up.
Originally Posted by bustert View Post
on the graphs, you can still see variation, point made. vented out the timing plug basically just tightened the graph but diff'l is still not that great.
it is like going down hill with skates one with dragging bearings and one with well oiled bearings, gravity being constant, yes there will be diff'l but not by much.
remember the ole brain tester?
drop a pound of marble out an airplane and a pound of feathers out at the same instance of time at 5k feet, which will hit the ground first???
back to the graphs, this will all change with even the slightest of change with a controlled variable. put this out on the track or road, was a good tool anywho.
i know you are a hot rodder so you know a run in the morning will be diff from a run in the afternoon.
Originally Posted by Hippysmack View Post
Why is the ratio of positive and negative pressure important?
It takes a balance of the two to run a Sportster engine.

Piston upstroke creates negative pressure and suction of oil from the sump.
It pulls oil up in the form of oil mist to be tossed around on the moving metal parts.
So it is important for lubrication and it does keep down aeration as you mentioned.
But without the reciprocating piston downstroke, there wouldn't be a lot of force to help splash it around other than the spinning wheels.
The upstroke pulls oil into suspension (air/oil mist) so the downstroke can help blow the mist around working in conjunction with flywheel and cam rotation.
Negative pressure is also important for ring seal as it allows the rings to fully seat on the bottom of the ringlands during upstroke decreasing blowby.
Too much negative pressure is detrimental to oil scavenging as it allows more oil to be pulled up into suspension instead of moving toward the scavenge port in the sump.
The bulk of gravity oil on the sump floor is heavier than the moving air.
But the spinning action of the flywheels can pull that oil up to be slung around the wheels creating more drag as it does.
So it's important to get the excess oil in the bottom out of the engine as fast as possible to keep down flywheel drag.
That's where the positive pressure comes in.

Positive pressure is important for oil scavenging as it works in conjunction with splash lubrication as well as the suction of the oil pump.
The positive pressure generated by the downstroke pushes oil toward the scavenge pump to be sucked vertically into the oil passage to the pump.
So there is a balance of positive and negative pressure that has to be maintained for overall engine operation.

The role of positive and negative pressure can be confusing.
Even though there is a positive 'push' on internal pressure through piston downstroke, the overall internal pressure is still negative.
It's just less negative than it was before the downstroke. This creates a pulsing effect on oil in the sump which helps shift the oil toward the scavenge port.
Even though there is normal blowby throughout the RPM range, the vacuum created buffers that.

The dyno charts are, of course, specific to the test subject and each engine is different.
That dip is a sliding figure depending on specific engine conditions and yes ambient temp conditions.
I have tuned my carbs different in colder weather on V-8s at times to compensate.
Originally Posted by bustert View Post
while there maybe some little of that going on, not as much as you think. i have been inside many industrial engine blocks while running hunting down issues.
the majority of pre-jet engines oiling is from connecting rod sling off and some from wheel shaft drain off, or head drains to the shirt.
stop and think, closed system right. if that is so, when the vent closes, the back flow would be nil, this has to be so because the rings need the vacuum to assist them. if you have oil pooling on the floor, the wheels could pick it up but for the piston up wash to suck up pooled oil, do not see that happening.
from pictures you showed, the newer oil jet engines are more open and open at the top more so that in the past. if that is so, piston up wash would draw from the least resistance and that would not be from the floor.
as an after thought, inertia from wheel wash would have the tendency to remove aeration, so where would be the next source, well, it is the cam gearing and i speculate that this is way more that the wheels present.
while there is fluctuations in pressure, law of averages is dominate be it below or above atmospheric. when time and excessive or vent over-run happens, the system goes positive and the magic numbers are already shown by posted testing.
the only way for you to be certain is electronic monitoring.
remember, the positive or diff'l will be a very small part of the cylce so the pressure to lift the valve off seat will be a narrow band also. bb in/ bb out, or blow by in / blow by out.
well the bondo must be dry by now, gotta go shape it.
Originally Posted by Hippysmack View Post
The hard part about this subject is that the whole pressure system has to be taken into account at the same time.
We also speak of blowby as in compression getting past the rings and into the crankcase.
But that can also work in reverse especially on engines with worn rings which is another factor.

I kind of think of it more of a closed system with an intake air leak (blowby).
You are right, the changes are small when things are going good.
And truthfully, this is all a talking point until problems occur.
As with the op with oil puking out the oil tank;
Knowing what should be happening inside sometimes clues to why it happened and how to diagnose and fix it.
I believe you can pull up too much oil in suspension which is compounded on the next cycle and it gets ugly after that.
So as long as everything is percolating, changes are small.

I believe it is 91-03 engines with the largest splash holes in the cam wall (91-99 in particular).

They blocked those off with the piston squirters in 04 which bottled up the CC leaving the pinion bearing as the only vent port to the cam chest.
They closed off the top end otherwise including moving the heads drains to the cam chest.
But they also have the flywheels with the cups cut into the ends for the crank sensor.
So the wheels are no longer slick on the end which is bound to pick up more windage.
Think about it, they didn't have to cup the wheels. They could have installed a trigger on the face with a horizontal pickup.

I don't believe upstroke picks up raw oil but rather oil mist.
The wheels can pick up mist from the sump which compounds around the wheels which is the reason for windage trays.
The fluctuations pulse air/oil mist that is picked up by all the moving parts.
So upstroke play does a part in lubrication however slight.

On a separate note, I am working on a homemade slack tube.
Made the fitting and got a hose. Just have make a backplate.
I've not put the device together yet but did a test with about a 7'piece of Tygon R3603 just to see if I needed a valve and I don't.

With the end open, pressure spit a slight mount of oil mist in the bottom of the tube but no more.
And that slowly crept up the hose.
When I put my finger over the end, vacuum slowly pulled it back toward the engine.
Water added should create a restriction to keep it on the vacuum side.
Diagnosis begins before teardown, during and after rebuild.

In Search of Fuel, Sunshine and a Steady Idle.

Reference the XLFORUM'S Sportsterpedia
for additional technical information & advice

Last edited by Hippysmack; 27th October 2019 at 06:37..
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