necessity of oil breather?

Discussion in 'Small Block Tech' started by David Gramlow, Mar 19, 2002.

  1. Ok, call me ignorant...what exactly is the purpose of the oil breather from the left valve cover to the air cleaner housing? It routes fumes back to the cleaner to be burned again, right? This is on my 72 350 4bbl. What would be the result of NOT having it in place? I just got alum valve covers, and I'm trying to figure out the holes needed. How do the stand-alone air breather/filter assy's function differently? Do I need a special oil cap to fit the thicker aluminum cover? Can any good machine shop do the holes for me? Thanks for any input.
     
  2. 72skylark

    72skylark 4 Doors of Fury!

    actually the breather kinda acts both ways. When the motors going and the PCV is open it sucks up the crakcase fumes and the breather lets air back into the crankcase. At idle when the PCV is closed it lets crankcase vapor escape and get sucked into the engine through the air cleaner.
    You do need some kind of breather. I'd suggest a indepentant chrome one, the type that have there own filter and don't connect to the air cleaner.
     
  3. Darryl Roederer

    Darryl Roederer Life is good

    Take note here!!!

    I'v seen more than one high mileage buick 350 blow oil out the rear main seal if the PCV tube is not hooked up...

    I'm sure it has a lot do do with a bad seal, lots of piston ring blow by, etc, etc....

    I'm guessing the "suction" of the PCV helps keep the oil from pouring out the openings that time has created.

    Also, I'd be willing to bet that sucking the dirty fumes out of the crank-case will make the oil last longer, and keep the engine cleaner...
     
  4. I'll have to continue to use the breather from the VC to the air cleaner housing. Last owner put on a Carter AFB Comp Series carb(625cfm), and an Edelbrock air cleaner housing, and punched out the access hole for the adaptor to attach the hose from the valve cover. Shouldn't there be a filter mounted inside the cleaner housing where the hose is attached? There's no oil around the opening on the housing, but the breather hose has plenty of oil inside. Would my local NAPA have a replacement breather hose? Mine is 2 pieces spliced together, and one is kinked pretty bad. Also noticed tonite there is an uncapped vacuum line on the carb. What drivability issues should have tipped me off on that?
     
  5. JohnK

    JohnK Gas Guzzling Infidel

    Carter AFB Installs

    Hi David,

    I normally don't post over here on the 350 forum, but the Carter AFB stuff is something that I just went through. I recently bought the Riviera, and a previous owner had replaced the original AFB with a newer style 9635 AFB, 625 cfm. With all sorts of installation mickey mouse bullshit for me to fix. So I rounded up all the AFB stuff I could get my hands on from Edelbrock and Federal Mogul. Since you didn't mention what vacuum nipple is open, we'll just have to run through all of them:

    Front of carb: big 3/8" goes to PCV valve. Pinch this hose off and idle should drop ~50 rpm if everything is working correctly. Front passenger side 3/16" nipple is "ported" or "timed" vacuum, not normally used unless you have that thermostatically controlled vacuum tree screwed into your intake like the 455's have. Should have a plug - this is the only one! Front driver side 3/16" nipple is full vacuum for the distributor advance can, since you don't need a tee to run the aircleaner 'hot air' valve.

    Passenger Side of Carb: big 3/8" tube there is left OPEN unless you are keeping the charcoal fuel vapor canister. It is a fuel vapor vent. Between that and the fuel line fitting is a 1/4" nipple. Run a short piece of 3/16" hose from that 1/4" nipple to the last remaining 3/16" nipple at the bottom of the choke coil, this is necessary to keep your electric choke working properly.

    Rear of the Car: 3/8" NPT female thread fitting for the power brake and transmission modulator vacuum, if the fitting isn't on the intake manifold.

    Electric Choke Wire - don't use the ignition coil as a +12 vdc source unless you have replaced the resistance wire as part of an electronic ignition conversion. Do not use the alternator field wire either. Find or run a wire to switched ignition wire.

    More on the breather - You really need to fix this too. The vapors that the PCV valve suck out of the engine are acidic and they really need to get sucked out. They contaminate the oil. The kinked hose has gotta go. The stock hose is "formed hose", if you must run a hose, go behind the counter at the auto parts store and pick out something for a different application and cut it to fit. Regular hose from the reel that's sold by the foot will always kink. Like somebody else suggested, just buy a chromie that plugs into the grommet on the valve cover. It will go with your air cleaner.

    Smog Equipment: If you have the charcoal fuel vapor canister, intake manifold vacuum tree, or any other smog stuff that you need to keep connected and working, let me know and we'll figure out how to plumb the job.
     
  6. Thank you John!

    Thanks for all the great info John! Sounds like you had a mess to straighten out with your Riv. I can't imagine why the guy would have used the 9635 instead of the 9625 AFB.

    Sorry, I should have said it is the large passenger side 3/8 tube that is open. Since my GS is a 68, there's no charcoal canister, so it should remain uncapped? I wasn't aware of that. I'll have to re-check the others to compare to your comments. However, I do know that the 2 front nipples are opposite of what you describe they should be. The driver side is hooked to the vac advance, and the pssngr side is capped. Guess I better switch them. The PCV is set up correctly. If I could figure some way to close off the opening in the air cleaner hsng, I would do away with the breather tube, and use a stand-alone breather. I don't really want to buy a new housing just to do that. But I WOULD like to use a stand-alone with my new aluminum valve covers... I'll have to figure that one out before I get holes drilled. I appreciate the help! :TU:
     
  7. Just went out to my 15deg garage and checked out the carb, couldn't wait til tomorrow! I confirmed that the 2 small front tubes are opposite of what you said they should be. Driver side is connected to the vac advance. Also, the tube below the elec choke is capped, as is the larger one right next to the fuel line. You said they should be connected? Will the 3/16 hose fit well enough on those 2 different size tubes? Also, the electric choke appears to be wired properly. I traced the wire to the firewall.

    For all the stuff I need to change, it sure was running well last fall before I winterized it! I think I better get myself a manual for this carb. I see Carbs Unlimited has them for about $17.
     
  8. JohnK

    JohnK Gas Guzzling Infidel

    David,

    Aren't previous owners a lot of fun? If it were me, I would have bought the 800 cfm AFB the Edelbrock sells. The fuel bowl vent tube gets left open according to the Federal Mogul tech guy I called. He said leave it open, unless I have to have it connected to the charcoal canister to comply with local smog inspection law. He said do not cap it. Also, according to this same tech guy and the manuals I scrounged up, you connect the other two nipples on the passenger side. I used a few inches of 1/4" and a couple more inches of 3/16" hose, and a HELP! adapter to make up my hose. You can use spit as a lubricant to stretch 3/16" hose over a 1/4" tube though.

    On the air cleaner base, it seems like there's two small screw or bolt holes that hold on an elbow to connect hose to. You can fabricate a crude block-off plate out of aluminum, and screw it to the inside of the base. Or just leave the elbow on and find a big enough rubber plug for it.
     
  9. We sell small diameter hose where I work, and reducer hose menders also, so I should be able to use 2 pieces like you. I'll probably try the fit with just 3/16 hose first, it'll look better. Plugging off that adapter elbow on the base sounds like a good option too.

    By the way, is that open fuel vent tube the place to shoot in a bit of gas before I try starting it this spring? It's been "sleeping" since late November.
     
  10. JohnK

    JohnK Gas Guzzling Infidel

    No, you can't use that tube because there is a spring-loaded trap door inside the carb. The linkage for that sticks out of the air horn right on the front passenger side corner.

    Mine has been hibernating this winter too, I'll start it up and get it ready to drive this week. My plan is to refill the fuel bowl thru the fuel line, hopefully it holds enough fuel to keep the engine running long enough for the fuel pump to fill the lines and filter.
     
  11. I envy you getting your car running this week. I figure it will be mid-April before we get some days warm enough that I'll want to start mine up. I believe we're only expecting highs in the 30's for the week coming up. I hate ND winters... :af:
     

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