Beemon

PCV System on a 322

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So I thought I would try something new.

 

For starters, driving around town I have no oil loss at all. Rarely ever see high RPMs unless I really lay into the pedal. Before, my rear main seal would weep at idle and now, after a patch job, it doesn't. Yesterday I went to a local Model A swap meet to look over the flea market, and on the way home I had a really bad lifter tick. Come to find I lost 3 quarts out the rear main. Oil had fumed past the gaskets at the breather caps and pushed past the distributor o-ring, among other places. No visible vapors out the road draft tube. I'm not equipped to tackle the road draft tube restoration at this time, and realizing this is a crankcase ventilation issue at high RPM, I hit the web and came up with this:

 

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My valve covers used to be so pretty until it started bleeding from the nuts and breather cap. The PCV is T-ed right before the vacuum pump so it's getting full intake manifold vacuum. The problem I've run into now, is because at my best the engine idles at 15 inches Hg and the PCV spring weight is too weak to keep closed at that amount. I can scarce up a late nailhead PCV system, but did later nailheads pull that type of vacuum too? Or less? Either way, it's acting like a vacuum leak at idle when it should behave more like ported vacuum, or open up slowly as engine builds load.

 

This was the aftermath of the trip - 30 mins at 65MPH both ways:

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17309346_10155881960555830_3288697643544

17342532_10155881960535830_7775389354263

17361657_10155881960560830_3633413888406

 

BTW yes I'm back to electric choke, and yes I know the dashpot is screwed out.

 

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You've done a lot with this car.  Please refresh my memory.  Have you performed a compression test recently?  It sounds to me like the rings have some issues.  I would doubt the PVC system would handle that amount of engine fumes.

 

BTW, from the HometownBuick.com site, 56 Buick Product service manual:

 

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Yeah that's about right. I can't remember my compression numbers off the top of my head, but when we first broke the engine in, and a thousand miles after, compression was ok, albeit a bit lower than normal due to .030" pistons.

 

The issue I'm having is I think the filter medium right before the road draft tube is just caked on there. Even with the wrong PCV valve in the valve cover, and the other valve cover plugged with a solid fill cap, there is no suction on the road draft tube from the intake manifold. I essentially ruled out that the reason I'm having such significant oil leakage is because of crankcase pressure build up at high RPM.

 

BTW the mid 60's Buick nailhead PCV does not work. It is fully open, whereas the elbow one I grabbed off the shelf pulls partially closed. Looks like I need to find some type of spring that's above the one I pulled off the shelf. The nailhead one had A stamped on the plunger, whereas the shelf model didn't have a stamp. I wish there was more documentation on PCV systems and how they work, because it seems to be centered on engine vacuum. Guess I'll start looking at 327 or big block engines and see what they used on their HP motors.

Edited by Beemon (see edit history)

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When the vacuum pulls thee plunger closed at high vacuum levels, then the flow goes through drilled orifices in the plunger's core. The one you purchased is probably for a generic Chevrolet application.  The way clogged road draft tubes were "cleaned" was to remove them, lay them on an open floor space, then use a torch to light the oily residue inside of the tube, then let it "burn out".  That was back in the middle 1960s timeframe rather than in more modern times were such might even be illegal in some places.

 

You can probably find pictures of the early Chevrolet (1965-67) PCV system in the restoration catalogs.  Pretty simple.  A metal "cone" went over the road draft tube hole, with appropriate sealing.  The vacuum line nipple on the cone had a rubber hose which went to a screw-in PCV which screwed into a brass fitting on the carb baseplate on the rear.  NOT unlike what you did, just a different way of doing it.

 

On almost ALL factory pcv systems, the valve cover hole is baffled to prevent oil splash from being sucked into the pcv system.  It would be an "oil mist" in the valve covers rather than "solid" oil.

 

I understand the reason you plumbed it as you did, but a vacuum tap on the base of the carb would probably work better AND not expose the fuel pump diaphragm to things it wasn't designed to resist.

 

Just some thoughts,

NTX5467

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The valve cover cap is baffled already and also has a filter medium below the gromet - it is solid, not a breather cap (except for the PCV), and specific for PCV installation. The T is before the vacuum pump, so it should go straight to the manifold and not to the pump itself. As soon as I get this sorted, I'll post some part numbers for those interested.

 

About taking the road draft tube and burning the oil out of the filter... how do you know when it's clean? Will it burn off sludge that couldn't be hot tanked? Actually I don't even know if it was hot tanked or not, to be honest. On Willie's website, the only advisable fix for removing 60 year old sludge in there was to cut it apart and throw away the contaminated filter. That's something that's down the road for me, when I intend to do the lifter inspection around the same time I pull the timing cover and check the chain, lifters and cam (just in case something like a cam needs to be removed...). I can understand burning it out with maybe a couple years of sludge build up... will have to ask my grandfather if he ever cleaned it out, but it is definitely currently plugged.

 

I found a few sources for PCV valves for low idle vacuum. They mostly come off of late 60s high performance big blocks, most notably the 1968 Corvette 427BB. I'm going to be picking up a few. Another is a fixed orifice PCV off a 2003 GM truck.

 

Lastly, the Rochester 4GC doesn't have a PCV port. With the air cleaner, I can't put a PCV spacer. I thought about plumbing into the vacuum advance port with a brass T, but that's ported vacuum... When I switch over to the 57-61 timing cover with the modern fuel pump, the vacuum lines will go away and I'll plumb the PCV into that port on the manifold, rather than T-ing it into the pump line.

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Clean and rebuild the valley cover first.  That piddly little pcv valve will not resolve that extreme pressurization of the crankcase.  The only time I saw that pressurization was on some with a hole in the piston or all pistons with broken rings.  If revving the engine with one breather off causes a blast of vapor, you have bigger problems.

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There is no blast of vapor revving, but I think it's just the crankcase vapor has a negative pressure inside it. It's not allowing the crankcase to vent properly at highway RPMS because of the radiator fan I think pushing air into the crankcase. Good news is that running with the PCV seems to have dislodged some gunk in the road draft tube because it started smoking today at idle. I don't know how long that will last, but for the interim I was thinking of going and pulling some valve covers and valley pan off a later 401/425 PCV engine. I already want to go out for the aluminum rockers, so may as well. That way I can clean the road draft filter at my leisure. A PCV system is preferred anyways, I think.

 

Speaking of PCV system, this is what I learned today. They will not work with vacuum accessories, or at least the vacuum pump in the same line. The vacuum pump causes some type of turbulence, even when T-ed up hill from it, which causes the PCV to not work properly. When I blocked off the vacuum to the pump, it magically started working. I'm already planning on doing away with the vacuum accessories as it is, so this system can work for me at that time. For now, I'll continue to monitor oil consumption and the road draft tube vapors until I can dig in.

 

And as always, here's some part numbers.

PCV: #CRB 21229

Breather Cap (With Gromets): #BLK BK 7031691

You'll need 3/8s tubing like any other GM PCV system.

 

Also not tested, but I think it would be in the best interest of the system to install a 1-way check valve up hill from the PCV. I'm not sure how the PCV carbs worked, but I doubt they had a 1-way valve.

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When I upgraded the cam in my Camaro, the engine was at 10.5" Hg in gear at idle. The PCV is a calibrated vacuum leak in the fuel supply system.  Metering calibrations accommodate that, as well as the air bleeding in through the throttle shafts in the base plate. 

 

I was trying to get a little better idle and discovered that later 1970s L82 Corvettes had a different PCV part number.  They had a purple color on the bottom half of the valve for ID purposes.  The L82 valve had a higher flow rate and raised the idle rpm about 25rpm with no speed screw adjustments.  I swapped them out a few times and ended up back with the normal L48 valve.

 

Prior to this, I'd discovered a MOTOR Manual-type book which a local Exxon service station guy had.  It had a chart with PCV flow specs.  Most were close, with a few with more flow.  At that time, I didn't correlate flow with engine specs.  Seems like the norm was about 1.6 cfm?   Not all of the several manuals he had had this PCV flow spec chart.  The manual had some other specs I hadn't seen anywhere else, as total ignition advance (vacuum + mechanical) at 2500rpm, which were WAY more than the mechanical + initial setting we were used to figuring.  But this was at part-throttle cruising rpm so both mechanical and vacuum were needed in that operational mode.

 

As for torching the road draft tube, I saw that done a few times in the middle 1960s.  The tube was placed on an open section of shop floor, then "lit" with a blow torch until it burned on its own.  After a while, the fire would go out and the tube would be gently handled and any real obstruction (the filter?) would be prodded out.  Then possibly more torching.

 

A hot tank soak would be a good deal, but would have taken longer and cost more money.  In more recent times, a hot tank would probably be the best.  The OTHER side of tat deal is that the passages in the block which "feed" the road draft tube would need to be open and clear, also.  The torch worked quicker and achieved reasonable results.  IF the car smoked a lot, then accumulated stuff would grow back reasonably soon.  Could it be that crankshaft windage (at lower rpms) would pull air into the crankcase from the breathers and then force it out through the draft tube?  Otherwise, any smoke at idle would have come out of the breather or slots in the top of the valve cover?

 

I'm not sure why the concern with manifold vacuum per se.  The normal GM (and probably others) has an internal spring which will limit flow with the engine in gear, not just "out of gear".  My Camaro 350 went down to 10.5" Hg at idle in gear, against the brake.  Things worked fine.  The L82 valve has a tad more flow, but would also work at the same lower vacuum levels, too, I suspect. 

 

The only issues I had was after many miles, the PCV passages in the base of the carb would clog and need to be cleaned mechanically.  But that was well past 250K miles with oil consumption about 4k/quart.

 

NTX5467 

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Nice job Beemon

 

Similarly once my engine was cleaned up the extra vapors from the breather got the engine kind of grimy so I cobbled up this so it could be taken on an off easily - the motor had about 90k on it.  Here's some other part numbers. This PCV didn't hurt the vacuum and pulled just enough 

 

PCV for 322

 

Since the rebuild last summer this isn't needed. I did get a grommet to fit the road draft tube hole in the valley pan if I ever want to hook a PCV up.

 

An old sock over the valley oil filler/breather also works fine in reducing oily vapors from blowing back over everything.

 

Until you run out of socks.  Whoops.

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For crankcase ventilation to work you need 2 things, 1) a way for air to get in and 2) a way for air to get out. The air coming in must be filtered or dirt will be sucked into your crankcase.

 

On a draft tube system the way in is usually a breather cap and the filter is in it. The draft tube creates a suction when the car is moving, and air flows in the breather cap and out the draft tube, hopefully taking the crankcase vapors out with the air.

 

Draft tube systems left to their own devices would suck oil out. There has to be a way to separate the oil from the air. I don't know how the nailhead accomplished this, but for example on a Chevrolet 283, there is a can shaped thing with a series of baffles that seperates the oil and drains it back into the lifter valley. On a Ford 352, there was a steel or copper mesh like the one used in the kitchen to scrub pots. It can cake up with carbon and plug.

 

You need to get that draft tube unplugged, and the oil separator, if there is one, also unplugged. Just connecting a PCV valve isn't going to accomplish what you want. If the draft tube is unplugged, the pcv will try to suck dirt up the tube. If it's plugged, its gonna create a vacuum in the crankcase and probably interfere with ring sealing.

 

If the engine has a lot of blowby, draft tube systems tend to smoke out the tube at stoplights. It might just be a little. On the other hand, if you have a lot of blowby it can look like the car is on fire. I had a Ford like that.

 

Pcv can help. You still need a way for the air to get in, and a way for it to get out. The breather cap is the way for filtered air to come in, and the PCV valve is the way out. On older engines, this usually means putting the valve in the hole designed for the draft tube.

 

More modern systems put the breather cap on one valve cover and the pcv on the other. Any leftover breather tube hole would need to be plugged. This ventilates the rocker areas better but tends to leak more oil on the outside of the valve covers.

 

Now, about that oil scum around your breather cap. If your engine is not basically brand new, with perfectly sealing rings, its normal. Every old car I have owned with a breather cap did this.

 

No pcv system EVER keeps up all the time. The manifold vacuum cannot support enough flow for that without making the engine run like crap. When it doesn't keep up, oil vapors will come out the breather cap. In the 80s, they plumbed the breather cap vent up to the air cleaner. That just got the oil all over the air cleaner.

 

On systems that have the PCV valve in the opposite-side valve cover, there has to be a baffle under the hole to keep the oil from the rockers from getting sucked up the pcv valve. Some aftermarket valve covers omit the baffle. Without the baffle the oil consumption will be astonishingly high.

 

I wouldn't get too concerned about the flow rating of the valve. If you have a smooth idling cam, Dynaflow, high rearend gears, etc. then one from any similar displacement smooth idling automatic will be fine. Probably even a Chevy 350 one will be fine.

 

The spring isn't supposed to be strong enough to hold the valve shut. They basically rattle. They are open at idle. Its normal. Some early systems didn't have a valve at all, just an orofice to restrict flow. The downside is if the engine backfires, it can cause a crankcase explosion. The valve is supposed to slam shut and prevent the fire from getting to the crankcase vapors.

 

Supplying vacuum to a PCV valve is the tricky part. It is a huge vacuum leak. The trick is not making the car run like it has a huge vacuum leak. First, you are limited by the engine itself in how much air you can let in (the flow rating of the valve determines how much actually gets in). Then you must mix the air in such a way that it does not screw up the fuel distribution. This is toughest at idle. Just hooking it to a power brake nipple or whatever will not work well, you will have a horribly lean cylinder or two.

 

Almost all factory PCV systems mix the air with the fuel/air mixture coming out of the idle jets. The PCV port will split and come out right under them. Sometimes its built in to the throttle body of the carburetor, sometimes its a plate under, but in 99.9 percent of all cases, this is how its done. The other 0.1 percent don't work very well. If you cant mix the air in under the jets, you would be way better off with a draft tube.

 

Good luck with the project!

 

 

 

 

Edited by Bloo (see edit history)
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Ken, didn't see your thread pop up within the search, would have probably saved me some headache!

 

About my engine: rebuilt two years ago by a rebuilder who claimed to have done Nailheads before, but ended up being very knowledgeable in Chevy engines. Simply put, a lot of things are amiss and I find myself with a great displeasure of dismantling my engine more and more. Unplugging the road draft tube is one of those things on my bucket list. Right now unplugging it isn't much of a concern because I have a breather in one cover and the PCV in the other. The issue right now is that it's been sucking a little bit of oil. There's a yard near me with some mid 60s Rivieras, so my plan is to eventually go out there and pull the valve covers/rockers and oil baffle and just swap them on. I just got back from a large road trip and got 18 MPG with the PCV hooked up and 14 MPG without it.So there is definitely an issue with breathing in my engine, the stars just haven't aligned for me to tackle it.

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The pcv system, per se, is not the reason for the mileage difference . . . BUT the "controlled vacuum leak" from the additional "air" going into the induction system CAN be where the mileage increase came from.  THAT, to me, would indicate a carburetor with the fuel curve shifted toward the "rich" side of things.  It might have been rebuilt, but the internal air bleeds and calibrated restrictions in the fuel supply areas of the car CAN shift the curve in that manner as there are MORE things in a carb that affect the ultimate fuel/air ration than just metering jets.

 

Find a shop with a fuel/air analyzer and do an exhaust check for the fuel/air ratio.  Then run the engine "with" and "without" to see what differences might exist.

 

NTX5467

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While most likely the cause, I'd also like to think that it has something to do with all the venting of negative pressure in the engine block and putting less strain on the piston rings. Since the PCV valve was installed, I haven't seen oil pushed past the distributor o-ring.

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12 hours ago, Beemon said:

and got 18 MPG with the PCV hooked up and 14 MPG without it

16 mpg expected average for a 322. Most likely you got a short fill to calculate 18 mpg and a full fill for 14 mpg (maybe that run up to 90 mph contributed).  Mine varies like that on my cross country trips, but the average is near 16.

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"Venting of negative pressure"????  That pushes oil past the distributor housing o-ring?  On an "open" crankcase system?  Me perceives the tri-shields are not all aligned on those things!

 

IF there is enough accumulated crankcase pressure (positive in nature) to push oil past a seal(s) with an open breather cap, somethings "not right" somewhere . . . it would seem.  Even if the road draft tube was restricted, the "pressure" should have been visible coming out of the breather itself . . . it would seem, rather than building up and pushing residual oil past seals and gaskets.

 

There will always be a pressure bias during the compression stroke on the piston rings, especially the "compression ring".   On some drag racing motors, several decades ago, there was an orientation to balance the pressure on the piston rings for alleged better sealing.  That "theory" lasted only a couple of years.  "Pan Evacuation Systems" were more effective by using two Chrysler-style pcv system "caps" to connect to a bung welded into the header collector (the fitting has a tapered end which is angled and welded into the header collector on each side) to use the negative pulses in the header collector to "vent" or "evacuate" pressure from the crankcase.  This theory works pretty well and was adopted by many drag racers (where allowed).

 

In the earlier 2000s, the issue of "ring flutter" arose on the GM LS-series V-8s in Corvettes, usually with manual transmissions.  With EACH engine re-design, the width of the piston rings has become thinner and thinner AND with a little less tension against the cylinder wall.  Decreased friction is the desire, which relates into more power at the flywheel and a little better fuel economy, too.  On some of those engines, the oil economy was not good, yet on others, it was as expected.  The GM engine people didn't know what was going on and even bought-back some of the affected vehicles for study and testing.  On the manual transmission cars, some drivers would drive in town in "one gear" and not upshift, choosing to use engine rpm to vary the speed in THAT gear.  End result, higher rpm higher manifold vacuum (low load) in certain rpm ranges would make the oil rings flutter and NOT scrape the oil from the cylinder walls effectively.  The same engine could get 4000 miles/quart or 1500 miles/quart depending upon how it was driven (probably not exact figures, as I don't specifically recall the numbers, but they were similar).  The "fix" was an oil ring with a slightly different under-side scraper contour and a little more tension.

 

So . . . I tend to agree with Old-Tank on the variation of the mileage explanation.  There ARE reverse-pressure specs on the calibrations of the fuel pump fill nozzles as to when they're supposed to auto-stop.  Of course, there can be some normal manufacturing differences involved.  For example, if I use one nozzle on my '05 Impala, it will cut-off and with the "next squeeze", will only go another .10 gal before it does it again.  Most, though, will go about .40 gal before the final click off.  In ANY sort of mileage checks, consistency of fill is important.  In times prior, some drivers wanted to see the gas in the filler neck, right at the cap . . . in an effort to extend their cruising range on trips.

 

Perhaps there's a speed shop up there which has a chassis dyno for "test and tune" rental?  A way to check the air/fuel ratio under cruise and power, plus to see at what throttle activation level the power mixture begins to happen?

 

NTX5467

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All I know is that I got 18 MPG under consistent fill ups on the way there and 14 MPG consistently on the way back without the PCV.

 

I don't know what else to tell you guys with my oiling problems thus far. I didn't rebuild my engine, someone else did and obviously botched it. There's a virgin 56 322 complete in Vancouver, BC that I've been eyeing up. But this car is my only means of transport now and the PCV system has cured the problem interim until I can get into the road draft tube filter.

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