Positive Crankcase Ventilation

[Patch]

Well very sorry I missed this thread.

At the risk of coming off as tho I am wanting a slice of alimony and knowing this is an old thread it is also one that can tie in a better understanding of crank efforts and ring issues!

 

Skydoc is right to expect and receive a quicker response across rpm range.

Positive crank pressures are a result of the moving parts but, also in large part a result of blow-by!

 

The vacuum at the pcv (positive crankcase ventilation) is passive as in siphon only.

The cost savings on such a pcv is short term minded from the factories period, as it is very inefficient; but, please heed this experience, it is absolutely a minimum requirement.

 

I’d like to offer some acknowledgment to the tree huggers. A couple of the comments are correct but what skydoc has done, as is in addressing the concerns posted, is in fact to reduce overall emissions not increase them! And yet you huggers are correct that one piece of the effort is again not proper accepted practice so, what is the fix is a better argument than to fault the whole exercise.

 

Now Puc in his own way was on to something. The answer is and oil-trap, but it cannot be in the form of a P-trap.

 

Recently I posted and mentioned crank balance during normal engine operation; I assume we all read that I referring to active balance not weight balancing as I referred to effort.

So once again skipping over crank timing: We run 4 cycle engines thankfully (I could imagine the fun of justifying 2 stroke in any size room with even one tree hugger among us;) )

Out of the 4 strokes only 1 produces energy. the remaining consume.

The intake stroke slows the crank as it generates vacuum then the compression stroke slows the crank more and the exhaust stroke is a matter of time with little back pressure created by valves and ports (say 3.5 lbs)

By reducing effort on the intake stroke to achieve filling skydoc has realized a slight higher percentage of fill, meaning a closer stoichiometric, so a higher more efficient expansion/burn over the same stroke distance or duration but, time over distance traveled is accelerated has noted in the outcome!

 

What we performance junkies appreciate about easier air flows is gains that keep velocity up, which this will do if maintained.

 

What has been overlooked is the blow-by however!

 

So skydoc when can I expect my check? And when will you be offering an oil trap with a split pipe for drainage?

 

Patch;)

[circa1968]

Hope its ok to revive this old thread!

Pic attached of what I just installed to capture oil and vent the crank case.  The intake port @ the airbox, where the hose was attached, has been capped.  This is on the left side of the bike, so aesthetically, my girl now has a good side and a less good side....  This was sorta proof of concept and now plan to see if it can somehow be at least partially hidden but still accessible enough to eventually drain any collected gunk.  I think I will also paint the collector bottle black, save for a small window to watch the level of what's collected.  That might make it disappear a little better.

And yes, subjectively, she runs super, IMHO.  (Note: I also just had the carbs rebuilt and this was done at the same time I re-installed the carbs so can't really give a good before/after take on it).  Biggest goal for me was not to turn my beautiful new carbs into another gunked up mess.

Now, here's the interesting part:  I also just changed the oil and filled to the max line! (I know, a sin here)  Yes, a bit of oil blows out & is caught in the collector bottle but guess what? 

Oddly with the oil at the max level, to my ears the clutch whine is much less noticeable (again subjective, I know).  Does that make sense?  I read an older post here about a guy doing some anecdotal testing and he found that lack of oil in the clutch box contributed to the whine so he ran an extra oil line to the clutch box and swore it significantly reduced the whine.

Would that extra little bit of oil fill in the crankcase, from 1/2 way between the lines to top of the line, make enough difference in oil pressure or splash around, or whatever voodoo oil magic happens inside of there, to reduce the whine? 

[Patch]

"Pic attached of what I just installed to capture oil and vent the crank case.  The intake port @ the airbox, where the hose was attached, has been capped.  This is on the left side of the bike, so aesthetically, my girl now has a good side and a less good side....  This was sorta proof of concept and now plan to see if it can somehow be at least partially hidden but still accessible enough to eventually drain any collected gunk.  I think I will also paint the collector bottle black, save for a small window to watch the level of what's collected.  That might make it disappear a little better."

 

Well Bro as far as looks go

But as for the rest, its a NO CAN DO nor should!

Also possessive crank case venting is a term we still use but in fact  that is not correct. We actually run a negative pressure crank case venting systems since the midish 80's...

The way it reasons is that of a sealed crank case would develop so much positive pressure it could in theory stop  stop a pistons down travel, in reality tho more like slow it! Worse yet is that it will blow oil throughout all the sealing gaskets.

Taking it a bit further for you thrust of knowledge: Because we know your engine compression marks this mod now,   is most likely not nessary, meaning your blowby must be at or very close to design expectations. Even if you hadn't of note which were like 5ish lbs. higher I could of bet which cylinders were higher than the others just by reading the plugs.

So there you have it, too much or excessive oil in the box is one of 2 things, poor maintenance or, low compression reading!

How ever and because I like the setup you fabricated I am forwarding you a cheat  but first let me explain something: I am a theory guy, my kick  is 4 stroke combustion, I rarely post specifics as relating to models. That said and to address your mod here is what I would consider as a viable correction: maintain the structure as shown  above: insert one rubber reducer washer as used in plumbing fixtures such as shower heads.... Unstuff the vacuum port in the air box  good to go! The low pressure is actually a know average say less than 4mbars so without that or say 0 the system is @ atmosphere, meaning you would lose every argument from every tree huger every every where you go....

You haven't kept up with your studies I see, think hydrocarbons 

[circa1968]

@Patch Hi Patch,  Could you repost with plain text?  For some reason, it shows up as black hihlight on black text on my computer!  Can't quite read it  Thanks!

[circa1968]

3 hours ago, circa1968 said:

@Patch Hi Patch,  Could you repost with plain text?  For some reason, it shows up as black hihlight on black text on my computer!  Can't quite read it  Thanks!

@PatchDisregard, I was able to just select the text and then the highlight goes away so I can read it.  Thank you for the feedback.  So, are you saying I actually need the vacuum @ the airbox to properly vent (pull) any blowby that makes it into the crankcase?  So far, on a couple of short rides it does collect a small bit of oil and other vapors so it seems something is pushing it out, or perhaps there's some venturi effect going on through the venting.

My original plan was to route the output back to the intake port, as you suggest, rather than vent to atmos via the filter.  I've read here others vented their 1st gens to atmosphere and at least one 2nd gen so thought I'd try that first. 

Well, I have as much interest in arguing with tree huggers as I have in arguing with an actual tree.  Both would be equally useful to me.  But for the sake (fun) of argument anyways, as far as I'm concerned, once we extract the dead dino's, those hydrocarbons are out and not going back in, seems like semantics of what games are played with them in between - they are out, staying out and not going away to some magical place.  So, to me the argument is extract or not, rather than what to do once out.

Here's my logic:  If 99% of a combustion cycle's hydrocarbon exhaust goes out the tail pipe then 1% blows past the cylinder rings & goes into the crankcase.  Let's say we have a perfectly efficient re-circulation from the crankcase back into the combustion chamber of that 1% blow by.  Then 99% of that 1% is getting put out the tail pipe on the next combustion/exhaust cycle anyways.  What I'm left with then is oil vapor, moisture, etc infiltrating my carbs, gunking them up, creating carbon buildup and less efficient motor operation all together.

So, as you pointed out in a prior post on this topic, more tree hugging harm than good,  yes?

Yes, grasshopper has studied a bit...😉

 

 

[Patch]

Funny "Grasshopper " was a thing between Puc and I some time back....

So I thought of writing out a painful memory I think the year was 1980 then nah I thought it still kind of hurts.

Here is the basics on what happened: I owned a third of a car mod shop long time back. I was still travelling most of the year but I got to play when ever I landed in town so, I decided to resurrect a project car in a rush after booking a couple weeks off. Long story short I lost the oil cap on her first run down the H.W./ Smoke was just overwhelming in the car and out the back! I pulled over discovered the missing cap which also had the chrome vent top above the cap seal on a set of M/T Covers... Well there I am between there and nowhere eh so I stuffed a rag in the valve cover right down to the oil separation plate; makes sense right! 20 minutes later i began seeing smoke again, chit another 20 minutes I'll be on base so pushed on Pulled into the lot cut the engine ran to the front to lift the hood, as I unlatched it well she blew the top off the engine! (lucky I wasn't sitting above it)

I have fooled with many kinds of engines and there just isn't a very good system when it comes to venting the crank fumes, yet it is a must. No I don't think venting fume to atmosphere is a good idea especially as in this case there is potential for ignition!

I've been rereading the thread and seems to me not all the bases have been covered. 

Lets break it down: we know we can't have a closed crankcase but why? Expansion and the forces hat accompany it. So the root is expansion then. The expansion in a crankcase consists of hot gasses, fluids and of course the solids: as they heat up they displace everything that is present in the container/crankcase. If left uncontrolled  they will overcome any lesser counter force of resistance such as seals, gaskets and the displacement of the pistons as they travel.

So we design venting system that control these unwanted counter forces thru crankcase ventilation systems. Seems simple but is it? How many forces are at play? What are the dynamics that hinder consistent venting in a looped system?

I am sure I will miss some items of cause but in general:

first off there is no 99% efficiencies in any of the engine I've worked on or know of.

Compression rings lockup where/when in the cycles? Are they locked up on the exhaust strokes? Which fluid must be replenished with every stroke, and where does it end up and, what does it carry with it? How many bikes are running overly fat jets? Depending on engine condition say good, a naturally aspirated motor is less than 70% efficient depending on RPM and as mentioned condition.

The vent tube on these bikes is a dead rise with a S shape, oil droplets are heavier than vapor the droplets should reverse direction for both reasons.

The vacuum as mentioned is low between a 1/4 to 1/2 pound so from where is the lift coming from? Or is there a dynamic at play with the vacuum?

Well yes there is  dynamic at play actually more than one. First consideration should be to test compression, the lower the number the more blowby there is. Next check for flooding which washes the walls reducing compression and collects in the crankcase. Now picture the case where you have flooding then making its way to the crankcase then venting out to atmosphere right by the engine and where you sit.

Vacuum dynamics: so we are dealing with low vacuum as mentioned however all bets are off when the throttle is chopped. The oil rushes forward still being spun around by the crank, pistons are racing, ring are fluttering/oscillating blowby increases and the lift forces push while at its highest vacuum.

Rapping up, yes mod if that is what is required but do so with follow thru, vent aft of the riders, or and better yet separate the fluids but burn what has yet to be burned. Remember motorcycles are not your fathers Buick  they are meant to be pushed true but designed to be maintained.

Well dat's all folks

Edited January 27, 2021 by Patch

[circa1968]

Thanks @Patch!  This grasshopper just got a little smarter.  Been reading a lot about open vs closed loop crankcase ventilation and will get rid of the vent and go back to a closed-loop - with the catch can.

Sorry, I wasn't suggesting the engine is 99% efficient.  The only thing I know in the entire universe which is 99% efficient is me, in my proficiency to do stupid stuff!   I just used 99% as a strawman argument about how much of the exhaust gas is exhausted vs blowby/recycled through the crankcase ventilation as to why the tree hugger argument does not impress me.  Once again, once we dig up the dead dinos, its out and not going back in, regardless of what this or that agency requires.  (And once again, for the fun sake of argument.....If the world was once a lush, tropical paradise with man-eating dinosaurs and we're slowly taking ourselves back to that, minus the dinos.....why is this a bad thing?😀)

I will go back to my original plan of just using the catch can in the as-designed closed loop system. 

As always, I'm here to learn and always appreciate and humbled by the knowledge that is shared!!!!

[Patch]

This club is certainly the best I have experienced in my time sharing over the net. New members such as yourself are a treat to us! We are a mature bunch with a diversity of experience aching to share our hard earned lessons. Thru the questions we stay sharper and reminded of our early days. Not always easy to understand the questions or the order in which they are presented sometimes but, only serves to make us dig deeper.

In your case tho this was pretty easy as we knew what the compression numbers are; again this shapes our thinking. I can't stress enough the value of knowing engine compression, it shouldn't be viewed as a boogeyman.

Remember how this thread started years back, one member expressing a fix for another. Agreeing or tweaking a thought should only serve to help refine and shape. I liked how you approached the problem however I do not equate the issue to your bike, know what  I mean.

There's lots that can be said about treehuggers: My Ont. friends can stipulate to the consequences of "acid rain" up in the Nickel belt. Dead forest as far as the eye could see. Still even to this day if you debark and walk some 50 feet past the newly planted vale of trees the tree graveyards remain standing. I showed my boys this some 10 years back. So these green naggers do force us to face facts while asking us to be a man and, find better ways.?!

[circa1968]

Yes, I poke fun at them, only because of some of the extreme positions but I love nature and also believe where we can, we should do better.   My biggest issue is where they use the "environment" as an excuse to command control over too much of our lives and in the US, we have such strong special interest (deep pocket) control over our gov't, which then has control over us, that so much of this stuff turns into protecting profits and/or large gov't employee unions and the balance of power, first and foremost.  The truth dies a sudden death when either of those are at risk, IMHO.

Industrial processes and output has vastly and necessarily improved over the years for protecting both people's health directly and the health of the environment.  But, I always question if ethanol, solar panels, electric cars, etc are truly a net benefit or just pushing chairs around on the titanic, or is it just a way to provide profits to well-connected individuals and companies - in the name of environmentalism.  Are you 100% certain those trees died of 'acid rain' and not some other natural phenom (like beetles, some underlying volcanic activity, etc).  For example, the ocean emits more carbon dioxide, through natural processes, than all human activity combined.

I sincerely appreciate all of you being here, sharing knowledge and pushing me to learn more.  Such a great site and group!

[Patch]

Yes WE are certain, top down and I watch the progression thru the years as I traveled thru the belt.

We appreciate what you bring too! GH

[circa1968]

Ok, I removed the vent filter and routed the output of the little catch can back to the intake box.  So, this is now essentially the stock config PLUS the catch can.  Also, I did not modify anything else, including the stock hose which connected the crankcase to the airbox so in case this ends up being another of my useless hair-brained ideas, I can go back to 100% stock config.

Thanks again for the honest feedback and great advice!

[vzuden]

Where did you purchase your catch can?

[circa1968]

Amazon:  https://www.amazon.com/gp/product/B07Z1R2MSN/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Made a couple of modifications to it.  The elbows shown did not come with it and as I found out after a trip to Home Depot, they are not NPT but rather BSPP (British Std) so you if you want to use those, have to order them separately.  I found mine on ebay:  https://www.ebay.com/itm/Fitting-Hose-ID-1-2-13mm-Barb-x-1-4-Male-BSP-BSPP-Brass-90-Elbow/162893204537?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Also, replaced the the schrader valve core with a screw and an o-ring as I did not want there to be any accidental dumps of fluid.

I ]coated the gold-colored filter with 2-part epoxy to basically make it a pipe & then used a dremel to make a hole on the same side as the exit port, then epoxied a piece of aluminum from a can of Red Bull to the input side to act as a baffle or plenum so that input flow would have to go down through the mesh material before drawn into the output.  The mesh material is just stainless pot scrubber from Home Depot.

[Patch]

This little project of yours seem to have some cool refinements, especially like the baffle and the use of scrub-bud.

I thought some on this a couple days ago and came up with the purple or grey scrubs cut to 3/4" then a key ring threaded thru the top say 1/2" down as a pull and lock against slipping. If I were of mind to I might just insert that into the down pipe from the air box. What I would anticipate the webbing would catch the droplets while allowing the vapor thru then drip back down to the crankcase, also easily maintained.

Anyways the problem should first be looked as symptom of too much crankcase pressure.

So like what you did. Important to think thru fluid theories before altering flows: The P in PVC is the pressure side of the loop. The volume in the crankcase is of course greater than above it. The vacuum in the air box is generated by the intake strokes but,  the air box serves as a plenum with a fixed open aperture ! There is no guess work in the air box. As we know each time we expand or reduce areas in flow we change velocities as well but; in so doing we create a low pressure just behind the and in the direction of flow: so meaning the opposite happens when the flow area is enlarged! Take those basics and you can then apply that to the PCV tubing  So, that is where the loop goes from Positive to negative, or at  least should. This same principle applies to your catch or separator and in your case Gh. at the baffle. the flow slows after the baffle which drops the oil in the container just as it does in a vacuum cleaner!

One last consideration : We often read about drilling holes in the air box to get more air thru it, this is false what you end up doing is altering the velocity of the flow thru the plenum, that in turn reduces velosity performance and, low pressure at the PVC port!

Hope this  stuff helps enlarge your understanding of modification to the essentials of that 4 banger 1326 cc air pump   

Edited January 31, 2021 by Patch

[circa1968]

Thanks Patch.  Definitely no air box drilling going on here.  Appreciate the knowledge you share!

My concerns about putting some mesh webbing in the down pipe would be 1) it getting clogged and not knowing its clogged, 2) pain to get to for maintenance and 3) since its inline to a 4 cylinder vacuum cleaner that it could get sucked in, especially if it gets clogged up.

[Patch]

My English took a turn, I corrected the post above.. 

[circa1968]

So, a quick update on this little project after ~4k miles.  It has held up well and seems to be doing what I hoped it would - catching oil droplets before they get sucked into the airbox.  Attached is the oil collected after the 4k miles since installing.

I have not pulled the tank to inspect the airbox or #1 carb closely but just doing a quick visual look up under the tank, I do not see the buildup of oil residue that was previously occurring on #1 (left/shifter side, rear).

[Patch]

Right on!