Dual PCVs On Chev 350?

Yes, A PCV system has to draw fresh air into the crankcase somehow. The traditional arraignment is to use a PCV valve on one side and a Breather / intake filter on the other to provide the clean air supply. Two vacuum sources leave no way to introduce the fresh air.

yes, there are a few:

1) You'll have double the PCV airflow volume, which'll create idle and low-speed driveability problems due to lean mixture. 2) You won't have proper crankcase breathing unless you also install a separate breather. This'll create a vacuum in the crankcase, which'll suck gaskets *into* the crankcase at the valve cover, oil pan, timing cover, etc.

One PCV valve, one breather, one oil cap (which may do double duty as a breather or as an attachment point for the PCV valve). All other holes should be plugged.

sends out free engineering samples if you just ask, and their whole product line is on their site.

There is a new 'help' brand of misc. junk parts at most auto parts stores now, They have all the different types of PCV grommets. Or you could just get a PCV grommet and put a short fat stainless bolt in the hole to block flow and likely look good too...

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@hotmail.com wrote:

Anumber1 has it right. The original air cleaner had a hose going from the valve cover to the air cleaner providing filtered air to the crankcase. If you are using an aftermarket air cleaner with no provision for crankcase ventilation, go to Summit or similar and get a grommet and filter that will plug into it. Do not just plug the hole. H

What you folks say makes sense but here's the part I don't understand (sorry - didn't give complete info in my first post):

Aside from the PCV holes, the only other hole is the oil fill in the passenger side. The cap, which sure looks like OEM, is the screw-in, NON-breather type - in fact, it has the rubber gasket to seal it to the cover. The covers and cap were on the car when I got it - took them off to clean them up and found the rubber parts are toast. Anyway, it seems to run OK.

Although...it sometimes dies on cold start and it idles a little high - maybe to compensate for lean mixture? And, I've had trouble with oil leaks - maybe vacuum breaking the gasket seal?

I was looking for a plug in the auto parts stores but I just remembered the local hardware store has some polyethelene button plugs that might work. Sounds like I also may be looking for a breather cap for the oil fill.

snipped-for-privacy@hotmail.com wrote:

You don't have the correct air filter on it right?

Therefore you have no PCV intake into the engine. This can cause oil leaks. Sometimes the system builds up more pressure than the PCV can suck off and normally this pressure is just vented back into the air filter. Now, it vents out an oil seal...

The PCV system needs to be balanced with an air intake matching or better said tuned to the PCV suction.

Very likely you can get a filler cap with the vent in it for a 350.

If you have a bad air filter, you also will have issues with the carb freezing up because you also no longer have the heat pipe to the intake. This can happen in high humidity at above freezing or even turn it into one solid block of ice on the highway. It's 'not' fun realizing the gas pedal is stuck at 55 mph in a snowstorm.....

You also can't pass emissions in most places with a defective PCV and no hot air intake to the carb.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@hotmail.com wrote:

Because in most post-'66 applications, the one grommet contains a PCV valve and the other contains an elbow connected to a hose connected to crankcase inlet air filter installed in the air cleaner assembly with the hose fitting protruding outward through the air cleaner's sidewall.

Could well be...note that if your engine's whipped, even two PCV valves won't keep up with the blowby volume and the crankcase pressure will force the gaskets *out*.

Or see my previous post,

.

Yep. They're available with a self-contained filter mesh and external breathing, with the same twist-in base as your present flat cap. Don't have my Stant catalogue in front of me or I'd give you a number.

DS

Hardware stores sells all kinds of plugs. I've got plastic ones and chrome plugs I bought when one hardware went out of business. It sholudn't be to hard to find one to fit the valve cover.

Harryface

05 Park Avenue 91 Bonneville LE, 303,383 miles

OK, the pieces are falling into place thanks to you folks' help. Again I apologize for giving less than complete info - should've realized all this stuff is interrelated. If I've got the numbers decoded correctly, the engine is a '74 Chev truck 350. It's in a '38 Plymouth coupe that probably weighs under 3K lbs. Supposedly the engine has about 50K miles. It doesn't burn oil, maintains a consistent 190 temp and, aside from the aforementioned starting/idle problems (which don't seem that serious), runs good. It's stock except for Mallory ignition, Edelbrock manifold, Holley 570 cfm 4-bbl, and dual exhaust on OEM ram-horn manifolds. It's hooked to a 350 auto with shift kit and a Nova rear - haven't checked the ratio but I expect it's in the 3.00 -

3.50 range. The air cleaner is after-market - basically a 9-inch round filter sandwiched between top and bottom plates. Carb freezing shouldn't be problem as I don't drive the car in cold weather and certainly not in snowstorms. For better or worse, we don't have emissions testing around here.

Apparently the PCV grommet and the oil cap are OEM. From the construction and fit of the plug, I assumed it is as well. But it doesn't have a part number like the PCV grommet and the Chevy parts guy couldn't find a listing for it. So now I'm thinking somebody blocked the breather hole with an after-market plug when the OEM manifold/carb/air cleaner were replaced. At this point the simplest solution appears to be replacing the PCV grommet and oil cap with OEM and replacing the plug with an after-market grommet and push-in breather - all those parts should be available.

Thanks again for everyone's help in working this out.

Well there's your problem- massive organ rejection! That Plymouth is allergic to the Chevy engine. It wants you to build it a nice shiny mid-50s 331 Hemi :-)

That sounds reasonable. PCV is one of those rare emission controls that turned out to be REALLY GOOD for engines. Continuously drawing fresh air into one valve cover, through the crankcase, and out the other valve cover really helps the oil last longer, reduces blow-by contamination, and reduces sludge build-up.

There's your problem. Plymouths aren't meant to have Chivvy engines. They're meant to have Mopar engines. You should've built or bought one of those, instead.

Yeah, yeah, I know the Chevy is sacrilege but it was in the car when I got it - I'm saving up for a hemi. Thanks again for the help.

Daniel J. Stern wrote:

If I'm remembering correctly (and I see farther down you said this was a '74 truck motor, and my dad actually has a '74 truck...) the one valve cover should have a PCV valve and the other one should have a hose going to a little filter that goes into the stock air filter housing (for fresh, filtered air intake to the crankcase.) You could do the same (last aftermarket air cleaner I bought included a knckout hole and a bolt-on hose fitting I assume for such use) or just use a push on breather, your choice.

nate

snipped-for-privacy@hotmail.com wrote:

You all probably are sick of this thread but I thought you might like to know how the project came out.

Upon closer inspection of the after-market air cleaner, I found an unused 5/8" hose nipple - pretty obvious but I still missed it the first time around. I got two new PCV grommets at the local Chevy dealer. The grommets have a 3/4" hole - course the valve goes in the driver side. For the passenger side, the local AutoZone has a plastic elbow ("Help" brand mentioned by Mike Romain) that is 3/4" on one end and 5/8" on the other - it's even a 45-degree bend which should fit better than a 90 would. It's listed as a Ford part. A piece of 5/8" hose to connect to the air cleaner and I'm in business for under $20, including new valve, hose, and non-vented oil cap. Pretty simple, but all your posts really helped me understand how the system is supposed to work and what I needed to do to fix it.

Now I just need to finish stripping the paint off the covers, which is why I took them off in the first place. Yes, somebody actually painted nice cast aluminum valve covers - a coat of primer and a coat of enamel. At least I don't have to take the blame for that one! Here's a tip - some stuff called Aircraft Remover made by Klean Strip (disclaimer - it probably causes cancer, impotence, and bad breath). I found it at Bumper-to-Bumper. Not cheap - $9 for an 18-oz spray can. But it works way better than the Bix I tried first - although it still takes a couple of coats and scrubbing with steel wool. The fins on the covers are polished and I'll buff them up with progressively finer sandpaper, ending with 1500-grit. By the time I'm done, I'll have $30 - $40 (and a whole lot of work) in them - about what a pair of chromed steel covers would cost but I think these are way cooler.

OK, bring on the wisecracks about Ford parts on a Chevy engine in a Plymouth coupe - guess that's street rodding!

Good job! Not to be nit picky, but is the 5/8 nipple in the *filtered air* area of the air cleaner? If not, you still need to put a filter in there. H

Yeah, it's inside the filter.

Thanks for the update, it is always really nice to know the outcome of the suggestions and fixes. Helps for next time.

I was at a Custom Street Rod show in Ontario Canada last summer and one Ford had the sticker on the tailgate, 'Built Ford Tough With Chevy Stuff!' LOL!

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@hotmail.com wrote:

one hole is oil fill, one hole is crankcase filtered air in, 3rd hole is crankcase air out (PCV), go cruise a junkyard with a camera, take pics and notes.