douvrin PCV musing
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default douvrin PCV musing

    Whilst cleaning out the inside of my inlet manifold I could not help notice it was coated with glazed oil and soot.
    I dont know if the previous owner had stuck a dirty manifold on or if the crap was from this motor itself, but none the less the crap was there and I dont want it to come back again.

    If there is one good thing about carby cars (and indeed there probably is only one thing) it is that the inlet manifold stays nice and clean.

    So I took myself for a path of discovery and looked at how all the different renaults I have achieve PCV.
    The way i saw it.....
    The fuego has a single outlet on the rocker cover going to a T piece which splits the line for a before and after the throttle plate.
    No filters, catch cans or anything else.

    The R21 has a different rocker cover design with a much bigger volume of air space in the baffled section of the cover. From this comes the same breather as the fuego, but a secondary small apature outlet with a yellow plastic cap that looks like a PCV valve (but is not a valve) going to the inlet side of the throttle, and the big hose goes to the filter side of the throttle and makes a big oily mess all over the throttle body.
    I guess at idle the smaller aperture (yellow cap) hose sucks a draft through the large aperture hose, and at WOT.....?? the smaller hose would do nothing and the bigger hose would take the fumes and oil and redistribute them all over my now sparklingly clean inlet manifold.

    Doing some reading on the net, and in particular the Toyota page,
    http://www.autoshop101.com/forms/h63.pdf
    I see that the fuego/R25/R21 system is called a fixed orifice PCV system.
    I cant for the life of me see how at WOT the inlet piping creates a low pressure in the PCV line by venturi effect with the crude plasic nipple, but having said that I have not mesured its effect either.

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    My agenda is simple, although its application may not be.
    I want PCV but dont want oil in my inlet.
    Sounds simple enough, but how do I achieve this??
    Should I use the fuego rocker cover, and simply put a sealed catch can full of steel wool in the line between where it splits into two and clean it out every month or so??

    or is there a more modern solution that is both environmentally responsible and does a good job of venting the fumes from the crankcase??? ($400 for an vapour pump is a bit steep at this stage in my budget)

    Jo

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    Quote Originally Posted by jo proffi View Post
    or is there a more modern solution that is both environmentally responsible and does a good job of venting the fumes from the crankcase??? ($400 for an vapour pump is a bit steep at this stage in my budget)

    Jo
    So, dry sumping the engine is out of the question? Would solve the problem, splendidly.

    Tim

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    bob
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    G'day Tim,

    the purpose is to burn off the nasty byproducts of blowby past your rings - dunno that that looks that well in print !

    This blowby creates pressure in the "sump" that we used to vent in the good old days straight out into the atmosphere - air we breathe. Now we give it a second chance and burn it along with the carefully measured A/F mix......

    The pommie way was to use a "valve" that only allowed this to happen when the manifold vacuum was high, so when you crested the rise on the western freeway after Bacchus Marsh there was this great cloud of white behind you.....

    So, you see, dry sumping is not quite what it's all about.

    And Jo, you need to condense out the oil so that it's not sucked into the manifold along with the blowby.

    cheers,
    Bob

    ps: Jo, condensing chamber in the old days was a steel wool loose filled container draining back into the sump - you don't need to take the blowby from the rocker cover, you can take it from the bottom end, old fuel pump hole ? old dizzy hole ?
    Last edited by bob; 25th April 2011 at 08:12 PM. Reason: explanation for young bloke.... :-)

  4. #4
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by bob View Post
    ps: Jo, condensing chamber in the old days was a steel wool loose filled container draining back into the sump - you don't need to take the blowby from the rocker cover, you can take it from the bottom end, old fuel pump hole ? old dizzy hole ?
    Thanks, old timer.
    Jo

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    Quote Originally Posted by bob View Post
    ...
    And Jo, you need to condense out the oil so that it's not sucked into the manifold along with the blowby.
    ...
    They call that a "catch can" these days . You can get them at most automotive stores.
    Lets just say we have a few pugs about!

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    Quote Originally Posted by Hipcrostino View Post
    They call that a "catch can" these days . You can get them at most automotive stores.
    Yeah, an oil air seperator is the way to go. As long as it is still sealed, it should be legal.

    An added bonus is that if you can release more crankcase pressure, you can also reduce the chance of seals leaking and even free up some horsepower lost through pumping loses.

  7. #7
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by mistareno View Post
    .....An added bonus is that if you can release more crankcase pressure, you can also reduce the chance of seals leaking and even free up some horsepower lost through pumping loses.
    That is where the challenge lies in a passive system.

    Jo

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    bob
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    G'day Jo,

    you used to be able to get a little "meter" to measure the crankcase pressure - there's one here somewhere, or used to be. Dunno if you can still get them ?

    Used by taking off the oil filler cap and holding it against the hole, there's a rubber disc seal on the underside. The reading side had this little plastic bead running around a circular scale.

    Seem to recall from when I had the old r12 that Renos always had a little pressure cos of the system that they used ? You could certainly feel the pulses on your hand when the cap was off on any r12 of the time. Never tried it on the Fug, have to see if I can find it......

    cheers,
    Bob

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    1000+ Posts jo proffi's Avatar
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    So.....some time has passed and I'm still learning more about this PCV stuff.

    I fitted a catch can, baffled with loose SSteel wool.

    At first I just connected the can to the valve cover, then ran the OE fixed orifice PCV system off it, which consisted of a small line to the plenum and a big line to near the air cleaner.

    Something was very wrong as the crank case pressure was high enough that oil was being forced past the rocker bolt seals.

    Too much packing in the can. doh

    I pulled the packing out and fitted a spacer in the bottom half of the can so the steel wool is in the top half only.

    Interested to see what would happen, I blocked off the big hose to the air cleaner and just ran the can connected to the rocker and being sucked by the vacuum of the inlet manifold off a small diameter tube. .
    In almost every situation in daily driving, the catch can reads 5 in-Hg of vacuum.

    At Wot, the pressure rises to only slightly pressurised (couldn't tell how much, the gauge is too broad in range and I was driving too hard), but in daily street driving, prolonged periods of WOT are rare .
    It is too powerful and speed limits are too low to stay WOT for any amount of time.
    Add a trailer and that all changes of course.
    Between gears the pressure jumps back down to 5 in-hg of vacuum quite quickly.
    I'm still waiting for sludge to build up in the can and drop into the collection bottle below it.
    That it has not shown any crapy soapy stuff makes me think either my hose to the bottle is too thin, or the soap is too viscous and is just building up on the steel wool,...... or that all the crap is being sucked into the inlet,....... or nothing is being sucked out of the motor and everything is honky dory.
    There is no easy observation port into the inlet manifold, and without pulling the manifold off, will just have to be content with not knowing what crap is inside it (for now).

    Jo

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    Jo,

    please be careful with steel wool - any fragments coming loose and ending up in the sump will damage the motor. OK for venting, but not recirculating systems.

    There are alternatives of a much coarser grade filter mediums that are safe, check out various existing oil breathing systems.

    Regards,

    fento

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    Quote Originally Posted by fento View Post
    Jo,

    please be careful with steel wool - any fragments coming loose and ending up in the sump will damage the motor. OK for venting, but not recirculating systems.

    There are alternatives of a much coarser grade filter mediums that are safe, check out various existing oil breathing systems.

    Regards,

    fento
    Noted.
    I used a well made name brand SS scourer complete, which is a non shedder. I'm as confident as can be that it will remain as a single clump.

    Jo

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    Rather than using the inlet to get a relative vacuum, you could go the other route and use the exhaust. This requires installing a tube in the exhaust, pointing away from the incoming gases, so that the expelled gases rush past it, creating a vacuum. This is called the Bernoulli effect.

    You'll need to install a check valve, as it will fluctuate from pressure to vacuum, and you'll also want to have a fairly free flowing exhaust from what I've read for this to work. The plus side is - any oil that gets sucked out no longer ends up in your inlet, it goes straight out the exhaust where it presumably burns off.

    This thread does a good job of explaining all the options: http://honda-tech.com/showthread.php?t=1199935

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    1000+ Posts Wildebeest's Avatar
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    Exhaust gas recirculation caused this problem on 240 Volvos.
    Incredible build up of carbon around the inlet valves. Reminded me of old Bedford engines!

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    You could install a vacuum pump.

    This ensures the crankcase is generally always in vacuum.

    I am under the impression that the extra power achieved will overcome the drive losses associated with the pump.

    I've never really looked into the way they are plumbed but I am under the impression that the suction side is connected to the cam cover at a few points whilst the outlet is connected to an oil air separator which dumps the oil back to the sump and the air back to the air intake.

    I believe the plus side is dramatically reduced chance of oil leaks.

    Some people use the old style air injection pumps as they are cheap as chips.

    Not sure if they would do quite the same job as a proper vacuum pump?

  15. #15
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by mistareno View Post
    I believe the plus side is dramatically reduced chance of oil leaks.
    That is my primary objective. No oil on the block and no oil in the plenum.


    Jo

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    Quote Originally Posted by Wildebeest View Post
    Exhaust gas recirculation caused this problem on 240 Volvos.
    Incredible build up of carbon around the inlet valves. Reminded me of old Bedford engines!
    Not what I was getting at. You use the vacuum from the exhaust (of course it fluctuates from vacuum to pressure so you need a check valve) to evacuate the crankcase. This does away with any need to use the intake, thus eliminating sludge. From what I've heard, you need a free flowing exhaust that doesn't have much back pressure.

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by callipygous View Post
    Not what I was getting at. You use the vacuum from the exhaust (of course it fluctuates from vacuum to pressure so you need a check valve) to evacuate the crankcase. This does away with any need to use the intake, thus eliminating sludge. From what I've heard, you need a free flowing exhaust that doesn't have much back pressure.
    I'm not sure that a pitot in an car exhaust pipe will generate much of vacuum. If you can restrict the exhaust , ie increase the flow velocity then you may have a chance.

    Also remember a vacuum derived via the benouilli principle is relative vacuum (or negative pressure).

    I would be taking some careful measurements with a vacuum gauge before committing too much effort into deriving vacuum this way.

    The vacuum will fluctuate in sympathy of firing strokes.

    I stand to be corrected: it's a long time since I done any fluid dynamics.

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    Quote Originally Posted by mistareno View Post
    Yeah, an oil air seperator is the way to go. As long as it is still sealed, it should be legal.

    An added bonus is that if you can release more crankcase pressure, you can also reduce the chance of seals leaking and even free up some horsepower lost through pumping loses.
    Exactly the point I felt was relevant - creation of an extra venting pipe in the rocker cover has been suggested (for the fuego) as being very effective in reducing oil leaks due to crankcase pressure forcing oil past the seals.

    At a RCCV event I actually looked at a Fuego that had been modified to reduce crank case pressure and it was the cleanest Fuego motor I'd ever seen.! Of course fitment of an efficient catch can system is the key to legality of this arrangement as long as the container lowers crankcase pressure and cleans vented air.

    Worth investigating Jo.

    Ken

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    Fellow Frogger! callipygous's Avatar
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    Quote Originally Posted by robmac View Post
    I'm not sure that a pitot in an car exhaust pipe will generate much of vacuum. If you can restrict the exhaust , ie increase the flow velocity then you may have a chance.

    Also remember a vacuum derived via the benouilli principle is relative vacuum (or negative pressure).

    I would be taking some careful measurements with a vacuum gauge before committing too much effort into deriving vacuum this way.

    The vacuum will fluctuate in sympathy of firing strokes.

    I stand to be corrected: it's a long time since I done any fluid dynamics.
    All vacuum is relative. You've got absolute vacuum, or you've got pressure. Kind of like you've got 0 Kelvin (no heat) or you've got heat. I think vacuum is, like zero temperature in Kelvin, a theoretical limit. So, I tend to avoid the use of the word vacuum for this reason.

    I don't know much about using this method to evacuate, except that it has been done, so it must work in some cases. I mention it as it may be worth looking in to, save having to rig up a catch can etc. provided it will work for your application.

    As for the vacuum fluctuating, yes, this will happen. A check valve takes care of this.

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    Quote Originally Posted by callipygous View Post
    All vacuum is relative. You've got absolute vacuum, or you've got pressure. Kind of like you've got 0 Kelvin (no heat) or you've got heat. I think vacuum is, like zero temperature in Kelvin, a theoretical limit. So, I tend to avoid the use of the word vacuum for this reason.
    .
    to be even more pedantically correct, vacuum is actually an absence of matter, not an absence of pressure. which is pretty funny because when i look inside the bag in my vacuum cleaner, it is certainly not empty of matter, and would probably be malfunctioning if i found it so.

    all that said, i think it is well understood that as used in this sort of discussion, vacuum means 'lower air pressure'.

    jo: another great topic, and i have learnt useful things reading about it as a result. i may have to rethink the strategy on my cars which consists of a fuel filter jammed in the hose which comes out the top of the rocker cover.

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    1000+ Posts Wildebeest's Avatar
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    Alexander,
    Fuel filter as engine breather? Super C and others have a nifty engine breather/filter for around $15.
    One of these would have a great "sucking through the teeth" reaction from your friend as you lift the bonnet!

  22. #22
    1000+ Posts jo proffi's Avatar
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    Woohoo!!

    THe bottom of my catch can has a line that in some cars would return to the sump, but I put mine to another catch can lower down where the Ac accumulator was, with a ball valve on the bottom.
    Its actualy a Gatorade bottle, but works just fine as a catchcan's catchan.

    Today it showed its first bit of collected sump snot.
    It is anything but oil colored, and resembles body fluid more than an oil based product.
    I'm glad it is not returning to the sump because I reckon its lubricating properties would be marginal.



    Jo

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    Nige, Is your catch can outlet connected to the manifold or is it just vented?

  24. #24
    1000+ Posts jo proffi's Avatar
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    It is connected to the manifold before an after the throttle, as per r 21.
    The only bit thats modded is the catch cans between the 2 hoses and the rocker cover.


    Jo
    Last edited by jo proffi; 11th October 2011 at 03:40 PM.

  25. #25
    1000+ Posts Wildebeest's Avatar
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    Jo,
    While all the preceding posts are interesting in theories and modifications I think it all comes back to the cause of the excessive oil breathing.
    Poor engine condition has to be the main cause.
    Then the condition of the PCV system. Blockages in hoses, perished hoses that collapse. Blocked manifold nipples [very small drillings] and faulty PCValve if fitted.
    Fitting catch tanks are usually a racing requirement not necessary on a road car.

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