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Beemon

PCV System on a 322

8 posts in this topic

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:

 

17353350_10155881960610830_7458133280009

 

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:

17352344_10155881960565830_1822871404179

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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Posted (edited)

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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