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Technical 327 pushing (dumping) oil out of breather, real head scratcher

Discussion in 'The Hokey Ass Message Board' started by Gonzo1717, Dec 18, 2018.

  1. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,998


    And even more leakage past the rings on the combustion stroke. That's when the pressures are the highest in the chamber.

    If there is enough leakage to blow the breather cap off, there probably isn't any PCV system that would flow enough volume to keep up with the leakage, particularly when the butterflies are vertical and there is little to no manifold vacuum.
    Old wolf, AHotRod and Rich S. like this.
  2. Perry Hvegholm
    Joined: Apr 16, 2018
    Posts: 113

    Perry Hvegholm

    Gonzo, I get it. At the drag strip, it's difficult to beat a DP for that off the line oomph. For the reasons I mentioned above. However, on a street driven car, where part throttle from stoplight to stoplight results in an extremely over-rich condition, the resultant oil dilution/ring wear becomes the problem.

    I still have to disagree with your "tech", though. A quality vacuum secondary carb (think Demon or Street Dominator) can be tuned to provide that gratifying throttle response, while also affording a reasonable expectation of wear surface survival on the street. The key here is tune, tune, tune.

    Catch can: Yes, that is what im referring to...sort of. The can will have an inlet from the PCV valve on the side of it. A valve at the top of the can routes to the carb vacuum source. It works by sucking oil laden PCV pull-over into the can....but only air leaves the can, with the oil falling to the bottom of the can. After some very spirited driving, even with a freshly rebuilt engine you will find an ounce or two of nasty, fuel laden oil in the can. Especially on hot days. The PCV pullover setups come in various sizes...from a few ounces to two quart bottle sized. I have a Summit Racing nearby, so I just buy their house version. It has an aluminum 1 qt can with a drain cock at the bottom to make emptying it a breeze. Looks nicer under the hood than the cheapo plastic bottle types.

    Here's an extreme version:
  3. Perry Hvegholm
    Joined: Apr 16, 2018
    Posts: 113

    Perry Hvegholm

    On a motor with proper ring seal, a functioning PCV valve is all thats required for evacuating blowby from the crankcase. If you swap to closed valve covers with a high flowing PCV and you find your dipstick being blown out of its tube and your oil seals failing, its time for a rebuild....or at least a quick and dirty hone and ring job.
    Old wolf likes this.
  4. Look around at the track, you'll se other cars with catch cans on them. See one you like, talk to the owner and get some tips. My engine is by no means a screamin' demon like the OP has, but I get a whiff of oil out the breather now and then when I'm exercising the beast and my build is fresh, under 9k miles on it.
  5. boring-hop-yard
    Joined: Feb 24, 2008
    Posts: 74


    I agree with 57 Fargo, 25percent loss to leakage is 25 percent loss of power. Time to refresh.
  6. boring-hop-yard
    Joined: Feb 24, 2008
    Posts: 74


    You might try thinking of it this way.
    Based on the fact you heard the hissing coming from the crankcase means the rings are allowing 25 percent of the engine compression to get by into the crankcase.
    Your breather is being asked to flow 25 percent of your engine compression through it.
    Your crankcase may be affected by your high volume pump or you may just have the making of a oil milkshake by having oil flung around and the high pressure in the case trying to escape via the breather (think blow hole), air pressure picks up oil and carries it to the top of the motor and out the breather.
    "My Opinion" you found the cause of puking oil by the fact the rings are allowing the compression to escape.
    I did a leakdown on a LS3 last month that had a 6 percent loss across all the cylinders and no more than 1 percent difference from the highest to the lowest across all the cylinders all coming from compression getting past the rings.
    I consider this to be a good used motor. If it was more than 10 percent loss or I found a cylinder that 10 percent loss under the rest I would tear it down.
    This is kind of like adding oil when you have a oil leak versus fixing it.
    Some add oil, some fix the leak, good luck on your quest.
    olscrounger likes this.
  7. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,158

    jimmy six

    I run catch cans on all my cars with PCV systems. Even my 2015 and 2018 have oil in them every time I check. More modern cars with injection and long runners are more susceptible to having the runners coated with oil film because the fuel is never in them. Engines with carbs and these new injector bodies not so much as the gasoline mixes with the oil vapors right under the butterfly plate.
  8. Jokester
    Joined: Jan 29, 2005
    Posts: 389


    [QUOTE="One peculiar thing that I am observing is that I am getting continued fouled plugs on the drivers side bank and lean on the passenger? Really driving me nuts.... but like I said, running hard! I originally thought that I had an extreme case of blow by on that bank of cylinders but, ironically the test showed that those cylinders had less leakage than the passesnger side! .[/QUOTE]

    Sucking oil in from the valley on the low side of the intake gasket on one side only???
  9. partssaloon
    Joined: Jan 28, 2009
    Posts: 422


    Last small block I did for a buddy who complained of the exact same thing, when I pulled it apart (fresh motor) it had ring gaps from .030 to .055 end gaps. (store bought hot rod motor)
  10. Sucking oil in from the valley on the low side of the intake gasket on one side only???[/QUOTE]
    I'd almost like to see how well the intake is sealing at each head surface.
  11. Doesn’t explain the leak down....

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  12. Joe H
    Joined: Feb 10, 2008
    Posts: 887

    Joe H

    I read a few pages back were the motor was broke in for 20 minutes or so at X amount of rpm which is great for cam but does nothing for the rings and bearings. It needs those 10 or 20 runs up and down the rpm range with the weight of the car to load the rings and properly break them in.

    Its time to pull out the wrenches and stop with the bandaids.
  13. Gonzo1717
    Joined: Jun 20, 2017
    Posts: 52

    from SoCal

    So tonight I decided to run through the gears without fear of oil mist. BIG mistake... when I got back home I had about a half a quart of oil puked all over my engine compartment and windshield.

    I want to say thank you to all y'alls input on this issue. I feel like the consensus is, it's due for a tear down. I really wanted to make sure all my bases were covered and rule out if there was some sort of error on my part causing it, I hate ripping sh*t apart thinking that something's wrong just to find out it was fine.

    Once again, thanks everyone for your prompt responses and knowledgeable input, much appreciated!
  14. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,507

    dirty old man

    Let us know what you find.
  15. We have a 289 ford that does the same thing. It will puke a quart of oil out in a 1/4 mile if you wind it up thru the gears. And we know why. the pistons & cyl walls are worn out. The new rings stopped the oil burning . but the blow by is excessive. To fix it properly it needs oversize pistons and machine work.
  16. Just a couple more thoughts: with the high volume oil pump, and the high RPM, there is a possibility that you are flooding the top end (valve cover area) with oil and the oil doesn’t have a chance to drain back and is being forced out of the breathers. Secondly, in my world of Diesel engines, most do not have any way of measuring compression or leak down. Most Diesel engine manufacturers do not publish compression specifications ether. We rely on what is know as a crankcase pressure test. You go to the road draft tube and install a calibrated orifice and a manometer that reads in inches of water. Navistar International specs say “No more than 6”H20 at high idle”. High idle is WOT in neutral with no load (on the governor). Six inches is not much pressure at all and any more and its overhaul time. I’m not sure how 6” would compare to 25% leakage, but I’m sure it’s way high and time for an overhaul. Just remember, in my world, ring seal is absolutely crucial in a diesel.

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    Blues4U likes this.
  17. Rich S.
    Joined: Jul 22, 2016
    Posts: 293

    Rich S.

    I noticed 3/8 hose mentioned a couple of times. Vacuum hoses are slightly undersized and measure in 32nds. I’m wondering if the hose is collapsing under high RPM, because it is not a vacuum hose.

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  18. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,998


    His breather that is blowing the cap off is in the intake manifold, not on the valve covers.
  19. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,541

    Kan Kustom

    I love these threads.
  20. Sorry, I read it wrong, thanks for correcting me.

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  21. a few decades ago a customer brought me a 290 cummins that the front main seal was leaking. So I replaced the stock seal with a C&R seal with a wear ring. The next week it was back with the rear seal leaking. So I pulled the trans, clutch & flywheel and replaced the rear seal again with a C&R seal & wear ring. Then it blew the pan gasket. I refused to work on it. unless we replaced the sleeves & pistons. The Rod bearings and main bearings had been receintly replaced. He got someone else to replace the pan gasket. and was back with the front main leaking again. We had words and I did not refund his money. He traded the truck. The next owner brought it to me. and brought a new set of liners & pistons and three rebuilt heads. And we inframe majored it. never touched the leaking front seal and It quit leaking.
  22. jackandeuces
    Joined: Feb 20, 2006
    Posts: 963


    Had the same problem along time ago...This may be a very elementary , have you checked to see if PCV ck valve is flowing in the correct direction...
  23. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,580

    from So Cal

    I ran that test many, many times when I was in that biz. There are a couple of different orifice sizes, you have to use the correct one for the engine. I kept a kit on my service truck with the orifice's and the tubing to connect them to the draft tube, and a flexible coiled up manometer.

    But we did modify some old injectors so we could run a leak down test on some engines. And we did check compression too, I think the tooling for that was probably OTC.
    Truckdoctor Andy likes this.

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