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Discussion Starter #1 (Edited)
there seems to be some misunderstanding about how the pcv system works on the V12 M120 engine. I took some time to study it, past 2 days.
below is the diagram.
It appears, I believe, perhaps ?
the vent tube under the intake manifold, is not connected to vacuum directly
it's connected to ported vacuum which is zero at idle.
the small vacuum lines that run to front right passenger side of engine,
that eventually run inside each intake manifold,
those are manifold vacuum at idle, and under part throttle and deceleration.
direct manifold vacuum, strong vacuum.
at idle, air is being pulled from the crankcase at position #1,
air is actually EXITING the tubes under the throttle bodies into pipes #9 and #10,
to replace what's being pulled out of the crankcase, with fresh filtered air,
that fresh air has already been filtered and metered, by the air filters, MAF sensors and IAT sensors,
so as to not throw off the fuel metering.
what goes in, must come out, back into intake stream, to be burned.
nothing is vented to atomosphere, it's a sealed system.
so any crank fumes/oil mist at idle, is exiting tube 4a into inside of manifold,
and the corresponding tube on the other manifold other side, unlabeled but visible.
this is how it works at part throttle, and idle, and deceleration,
when manifold vacuum is high.
at wide open throttle, manifold vacuum drops to 0 to 3" hg range.
there is no longer any manifold vacuum draw into #1, or #4a, or corresponding vacuum line other side
instead, PORTED vacuum under throttle body is now high,
due to velocity at heavy throttle opening,
and crankcase positive pressure it higher, due to more blowby,
the flow then reverses, and crank fumes flow the other way,
out of #8 pipe, into #9 pipe both sides, and into the throttle bodies.
a worn engine with bad rings will have so much blowby, pipe #9 will be puffing fumes visibly at idle. grey smoke.
seen many an engine like that in the old days.
my point is this- pcv was required to keep crank fumes in the engine,
and reburn them.
up until 1962-64 era in USA, pipe #9 did not get routed into carburetor stream !
it simply ran down the back of the engine, and vented crank fumes to the atmosphere,
under the car, using the low pressure area under car to pull fumes away from passenger compartment.
in the valve covers, was simply a breather cap, filled with wire mesh.
at wide open throttle, when the dump tube pulled the fumes out of crankcase and underneath car,
air went into the breather caps on valve covers.
no crank fumes entered the intake manifold at any time- it was air/fuel mixture only.
if you have a bad vacuum leak at pipes #8 and #9 under intake,
and don't have time to change it,
you can disconnect pipe #9 from both ends of the throttle bodies,
and block the port at the throttle body with a cap.
and also pull fitting #1 off the engine, and block those ports too.
the crank will be vented and breath through the disconnected #9 pipes,
and the vent hole remaining open in valve cover at position #1.
just cut off its vacuum source, it won't leak anymore,
until you have time, or want to, change it. it's a big job pulling intake...for a breather...
final point being, there should not and could not be a strong draw at #9 from throttle bodies,
and #1 from manifold vacuum, at the same time.
one side is designed to feed the other.
if it was drawing from both at all times, there would be a squealing noise from the crank main seals,
or valve cover seals, or oil pan gasket, or some other gaskets,
because there would be a high negative pressure inside the crankcase, pulling in.
it happened to me. I worked on a 4-cyl Ford engine once, in an EXP car.
we put a PCV valve on it. the car would squeal every minute or so when running.
couldn't figure it out. until I drilled about 5 small 1/8" holes in the oil filler cap.
the squealing went away instantly. it was pulling air in, from the front main seal and causing the squealing sucking noise.
the reason the M120 and all new injected engines are configured this way is,
PCV air must be metered by the MAF sensor first,
otherwise it will throw off the fuel injection metering, it will be lean all the time.
there also appears to be ports at #5 and #6,
I don't have the labeling for this diagram, but those do the same thing as the others.
either in, or out, or both, will investigate that further.
unless anyone has the labels key ?

crankcase ventilation system m120.jpg
 

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I don't know what 4a is supposed to depict. There is nothing like that on the M120 that I've ever seen. There is an unused boss on the top of the manifold near the throttle body that may have been intended for a line there. I have no clue what 5 and 6 are supposed to depict. Nothing like that on our engines.
You forgot to mention 4b. It pulls vacuum off the backside of the manifold on the driver's side, and sends it to the valve cover on the passenger side. That, and the two ports on the front of the passenger manifold provide vacuum to the valve cover. There is an oil separator in that block on the front of the right hand valve cover.

Actually, pulling a slight vacuum on the crankcase is good for performance, as it reduces pumping losses from the backs of the pistons.

Where did that diagram come from?

Jon
 

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Discussion Starter #3
if there is no actual internal passage, then #4a just shows that the air pulled in by vacuum, goes into the intake manifold plenum.

#5 and #6, yes I agree, that is a misdrawn image, because I have both distributor covers off my engine since day one, and there is no such unit in line with the serpentine fan/pulley/accessory drive belt. I looked today. it would have to be inside the block? is it in the valley cover under the intake ?

#1 is a rubber 90 degree fitting, that mates the 2 valve cover PCV outlets, with the 2 intake manifold vacuum fitting inlets. it's pretty easy to block, I blocked mine today just to see how it would act. it doesn't seem to change much, but if the engine had a breather tube leak, it would cut off the vacuum source to it.

#9 and #10 fittings are definitely outboard of the throttle plates, meaning they are not vacuum hoses per se. they are actually filtered/metered air outlets to the PCV system inside the engine, under the intake manifold.

it operates the opposite of what it appears, #9 and #10 air flows into the breather tube under the intake, and only reverses flow during wide open throttle positions, at low manifold vacuum.

the more piston ring wear, the sooner #9 and #10 would flow into the throttle bodies. blowby past the rings into the crankcase, and high throttle velocity when wide open, is what creates the reverse flow.
 

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Discussion Starter #4 (Edited)
the front ports are easy to block, remove rubber block #1,
put rubber caps on #4a and #4b
the small tubes going straight down into the valve cover are just open to atmosphere, they are not vacuum.
took the car for a ride, wasn't much different. the idle was a little more stable and lower though.
I didn't try disconnecting #9 and #10 from throttle body yet. they can be blocked with the same type of caps, just larger. I get them at True Value hardware store.
there's really no reason to push oil blowby fumes into the intake manifold, if the hose plumbing is old and cracked, the system can be disabled, at least temporarily.
I put #1 rubber block back in place after the test drive, and pulled the caps.
for now...
IMG_20190919_123910.jpg
IMG_20190919_123914.jpg
 

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Discussion Starter #5 (Edited)
JAL- I found it, mysterious crankcase evacuation part, does exist, here it is in video, you can see the evac port just behind left side intake valve cam sprocket, facing upward. all I think it does is tie the lower crankcase to valve cover area, to equalize pressure between crankcase and valve cover/cams area above cylinder head.

you can see it starts out as a rectangular opening behind cam sprocket, but when he scans camera down to below it later in video, it becomes a circular round pipe that goes into bottom of crankcase, it is an equalization tube. it vents crank pressure to valve cover, and vice versa.

the designers would not want any pressure buildup in any chambers of the engine internally, because it would blow out seals and gaskets in various places.

the spinning crankshaft does create a pumping effect in the bottom end. we need to get an engine apart and see for ourselves. anyone have a spare partial or junk engine laying around ?

you can see it right off beginning of the video by Victor

 

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Discussion Starter #6 (Edited)
go to time point 11:10 in this video, they drop a cylinder head on left bank to bolt down, the passageway in head for vent pipe is plainly visible.

later on at time point 15:12 the vent tube is visible in place, they don't show it being installed though for some reason. it appears to be superfluous ? because it looks like the passageway is open air from top to bottom in that sprocket chamber anyway ? i.e. why is there no vent pipe in the other right side sprocket chamber ?

perhaps they used the vent to avoid any eventual timing chain/gear tooth/guide debris from falling into the bottom of engine through the vent hole. this way only crankcase fumes can move from top to bottom, nothing else.

on the old American V8's that tube would be exposed sticking straight up, with a breather cap on it, removable for adding oil.

back in the old days before the PCV mandate for emissions, that's what they would have done. one could actually run that vent tube right out of the M120 V12 valve cover, and put a breather cap on it. with a dump tube out back. done. no oil fumes in engine.

 

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Discussion Starter #8
road draft tube, standard equipment until c.1964
red engine is ubiquitous Chevrolet small block V8
when the engine got worn out, and the road draft tube started puffing at idle,
we used to attach a long rubber hose to it with a clamp, and run it out back of car,
so the fumes didn't come inside the passenger compartment.

road draft 2.jpg
road draft tube.jpg
 

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Discussion Starter #9
found a bare block pic on google images, it is a an old post by a BenzWorld member, drivers side left block bank is offset to rear of engine in this design, the cutout for crankcase vent tube on that side is visible, half moon cut into the block, upper right in picture, appears to be vent from lower timing cover ? into upper valve cover. not the crankcase per se.


v12block.jpg
 

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it is a an old post by a BenzWorld member, drivers side left block bank is offset to rear of engine in this design, the cutout for crankcase vent tube on that side is visible, half moon cut into the block, upper right in picture, appears to be vent from lower timing cover ?
Lots of good pictures and information is in the old posts:


As you can see, what is labeled as #5 and #6 on the diagram provided in the original post, are hidden behind the engine front cover.
One is merely an oil separator and the other is the tube which can be seen in the video links (yes, there is a grommet where the half-moon in the block is).

Here is a picture of the front cover itself:


and a closer view of the U-shaped part of the block:

 

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Yeah, that schematic diagram makes those parts (5 & 6) look external to the engine, when they are hidden. The diagram also makes it look like the big breather assembly (7, 7a, 8) under the manifold is on the left bank side of the engine, when it is on the right bank side. That diagram leaves a lot to be desired.

Jon
 

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The diagram also makes it look like the big breather assembly (7, 7a, 8) under the manifold is on the left bank side of the engine, when it is on the right bank side.
I do not follow. The breather pipe runs between the two banks. The round canister appears to be in roughly in the middle according to this picture, which also shows #s 8, 9, and 10:

 

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It's between the banks, but on the right side of center.

Stop this video at 4:39, and you can see the attachment location for the forward end of the breather on the right side.


Jon
 

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It's between the banks, but on the right side of center.
Thanks, I understand now. Your complaint was that the diagram provided by the OP in post #1 shows the large plastic canister with connections in the center, when in reality, they are slightly offset.

2604875



By the way, for someone used to the Jaguar language - banks A and B - the use of left and right I see here is a bit confusing
 

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Discussion Starter #16
wow now we're cookin' with gas ! thanks you guys for all the further info, links, pics posts. we nailed it

my motto and policy is, there should be NO mysteries in any vehicle you own, drive, or service.
back in my younger days, I would buy GM A-bodies for $25-$75 nonrunning cars, and spend weekends disassembling them to the bare frame, just to learn how they went together, and what made them tick. it paid great benefits as a knowledge base in later years. there's nothing to fear if you know the vehicle and its systems inside out.

another mechanic recently said to me, to build an engine, you have to think like an engine.
very true.
to which I replied, you have to know the engine inside out,
you have to become the engine. it's an art form.

I have not reached that point yet with a W140...I doubt anyone has or will 100%, not even the engineers who designed it....it's so damned complex !
 

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Discussion Starter #18
I do not follow. The breather pipe runs between the two banks. The round canister appears to be in roughly in the middle according to this picture, which also shows #s 8, 9, and 10:

do you see the labels stating EGR tubes on either side ?
you can take thin stainless sheetmetal, cut it with scissors, double it up if need be,
and make small square blocking plates, sandwich them between the EGR pipes and manifold, use some high temp permatex as a sealer between the surfaces there,
bolt the pipes back to the manifold,
and permanently block the EGR tubes that way. that's what I'm going to do eventually.
 

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Discussion Starter #19
I do not follow. The breather pipe runs between the two banks. The round canister appears to be in roughly in the middle according to this picture, which also shows #s 8, 9, and 10:


if the front 2 small vacuum tubes are blocked, front of right side valve cover, it cuts off vacuum to that draft tube.
the draft tube is actually feeding INTO the center of block at idle, pulling fresh metered air from each throttle body.
without vacuum assist, that tube under intake, would become a plain old road draft tube c. 1962 or before.
now, draft tube pipes were then pulled off the throttle bodies completely,
and the throttle body outlet nipples capped,
and the draft tubes extended downwards to the base of oil pan,
presto, no more oil fumes in the intake manifold tract.
low pressure under the vehicle would pull the crankcase fumes out by itself,
and the mixture in the intake manifold, need not be diluted and contaminated,
with oil blowby mist.
there's good logic in a road draft tube, and no EGR.
oil in the gas causes detonation, in a gasoline engine
especially one with 10:1 and higher compression on pump gas,
like the M120.
the 2 small tiny pipes in the front right valvecover at front,
could be left open, to draw fresh outside air into the crankcase,
the road draft tube(s) pointing down,
would draw it out.
I say tube(s) because you could dispense with "T" fitting and dual tubes,
and just one run big tube straight downward,
like those big old American V8's did.
sure, it pollutes a little more,
but it's not like there's millions of W140's running around w/V12 engines in them today.
let the new cars worry about the emissions,
W140's are now an antique novelty.
tinker around, have some fun...
 

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Yep pipe is a tight offset fit.

No EGR on my old car but i did remove the air injection setup due to a bad bearing, gives the a cleaner looks with less clutter
 

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