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Thread: Too much crankcase pressure, novice engine builder
          
   
   

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  1. #1
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    Too much crankcase pressure, novice engine builder

     



    Alright, I'm a novice engine builder so go easy on me. I just built by first engine, a small block 400, Trick Flow heads, healthy cam, the works. She runs pretty well except one small problem: excessive crank case pressure causing oil leaks. I've gapped my compression rings with the intent to run boost relatively soon, so they're a bit excessive, I know. This, as I've learned, has the unfortunate consequence of building excessive crankcase pressure from the additional blow by. I tell you this information that you already know just so you know where I'm at.

    Now, originally, when this engine was in stock-ish trim, it was running a factory-style PCV system. Even with that in place, after my rebuild, it blew out the front gasket in-between the intake manifold and block (I believe this is referred to as the China wall?). Before knowing what the actual cause was, I replaced that with some heavy duty RTV and it seemed to work. Few days later, the timing cover gasket goes. At this point I realized what the problem may be so I added 2 vents to the valve covers in addition to the PCV system in place to hopefully help evacuate additional crankcase pressure. Unfortunately, while the oil leaks are "better", oil still manages to squeeze past the new timing cover gasket at high rpms.

    Now, to my actual question. I've been doing a lot of research and I believe a PCV system that doesn't rely on my intake manifold vacuum may be the solution. I went with as big of a cam that the rest of my components could support (naturally), so I'm assuming the vacuum pressure that the PCV system needs just isn't there, especially at high rpm when vacuum pressure is low and crankcase pressure is high. All of that being said, I've been looking for stand alone PCV systems and there really only seems to be like a pulley style pump, example below:

    https://www.jegs.com/i/Moroso/710/22640K/10002/-1

    While these systems probably work great, they're crazy expensive. My "never having dealt with this before" solution is to use an electric vacuum pump, typically intended for brake booster vacuum, but instead have it drawing vacuum off the valve cover/crankcase. Does that even sound possible? My main concern is that these style pumps clearly weren't meant to be drawing from as big of a volume as the entire crank case, but I'm interested in hearing other's feedback.

    Most importantly though, I'm looking to learn. If you've read all of this, I greatly appreciate your time. I may be completely on the wrong track here which is why I'd love input from others. Or, if you simply have a cheaper/easier solution, I'd love to hear it. If you need any additional info or questions, I will do my best.

  2. #2
    34_40's Avatar
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    Personally, I think you're looking to apply band-aids. Pull the pistons and re-ring it right. You'll never be happy with it otherwise.

    Just my point oh two.
    36 sedan likes this.

  3. #3
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    I have the rings gapped where I want them though. 26 thou on the top rings, 27 on the bottom. After speaking with a few engine builders about my plans for the motor and adding boost, this was determined a good gap that would ensure no catastrophic failures. I don't believe this is a result of too much ring gap, just more than initially intended for a PCV system that was meant to work with a stock cam. Which is why I'm asking for what people have done for solutions or ideas for better PCV systems.

  4. #4
    34_40's Avatar
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    Well, you asked so I offered. If you think you'll fix this now, wait 'till you setup and run forced induction!
    NTFDAY and 36 sedan like this.

  5. #5
    NTFDAY's Avatar
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    The bearings are next to go, been there, done that.
    36 sedan likes this.
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  6. #6
    36 sedan's Avatar
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    JMHO. but your ring gap of .026 & .027 is not large enough for a 400ci to cause that much crankcase pressure.
    https://www.enginelabs.com/engine-te...-ring-end-gap/

    Are you sure your rings are installed correctly? Did you stagger the gaps? Did you measure and file end gaps correctly? Is the cylinder wall to piston clearance correct?

    However, you could try exhaust evacuation (may not work well with mufflers);
    https://www.summitracing.com/parts/m...iABEgIFcvD_BwE

    And here's a Google search that brings up info on your electric vacuum pump PCV idea;
    https://www.google.com/search?client...&bih=631&dpr=2

    Have you done a compression check to see if you have a broken ring?
    Last edited by 36 sedan; 12-15-2020 at 07:29 AM. Reason: add last comment

  7. #7
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    The first thing you need to do in a case like yours is to do a cylinder leakage test to see where your problem begins-----------

    Also-what lube did you use on the rings/pistons when you built the block???
    By popular opinions-just a grumpy old man key board bully--But really, if you are going to ask for help on an internet site, at least answer questions about what you are asking about-----

  8. #8
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    My first thought as I read your initial post was to wonder if you staggered the rings properly, like 36 sedan asked. I second the suggestions that you should first do a compression check on all the cylinders (36 sedan), and then a cylinder leakdown test (jerry clayton). Blowing a timing cover gasket sounds like a lot of pressure! I'd be tempted to rig up a pressure gauge with a rubber stopper and plug it into the oil filler tube as you have someone blip the throttle just for grins.

    I hope that you'll come back with some hard data on what you find.
    NegativeZero likes this.
    Roger
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  9. #9
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    That was my thought as well, which is why I'm here. You only notice the pressure build up at 6000+ rpm. There really are no problems as far as I can tell below that. I made sure to double check that my ring gaps were correct (both in terms of gap and shape of the gap) and installed the correct way (they were staggered). I recorded myself building this engine and from what I can tell from the footage, it all looks correct.

    As for piston to cylinder wall clearance, I know it's not ideal but I'm confident it's in spec. I bought the block when it was bored 30 over. Because I'm working on a tight budget and I already had pistons that were meant for a bore of 30 over. I only had a machine shop do a cylinder hone and no more bore. As a result, the block isn't 100% perfect, but it's still good. I don't have the numbers written down unfortunately, but I know I checked them when I had everything apart.

    Static compression ratio is 10.1:1 Results of a cylinder compression test are as follows:
    cyl1 - 135 psi
    cyl2 - 130 psi
    cyl3 - 139 psi
    cyl4 - 132 psi
    cyl5 - 133 psi
    cyl6 - 137 psi
    cyl7 - 125 psi
    cyl8 - 143 psi

    In my inexperienced opinion and what I can tell from googling, these numbers seem fine which would mean the break in process was successful, correct me if I'm wrong.
    Last edited by NegativeZero; 12-15-2020 at 09:42 AM.

  10. #10
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    I've done a compression test, results in previous reply. Is there a difference between that and a cylinder leakage test?

    Lube used for assembly was Lucas assembly lube:
    https://www.autozone.com/greases-and...4oz/692400_0_0

  11. #11
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    A pressure gauge on the oil filler tube sounds like an interesting idea, definitely going to try to rig that up.

    I wish this was just a case of me using crappy gaskets, but I've replaced my oil pan gasket, timing cover gasket, and the RVT below the intake now and it works great for anything 5000rpm and below, but as soon as I hit 6k+, oil manages to start seeping out somewhere.

  12. #12
    rspears's Avatar
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    Quote Originally Posted by NegativeZero View Post
    Is there a difference between that and a cylinder leakagage test?
    Yes, the cylinder leakdown test tells you the ability of each cylinder to hold pressure over a short time. Here's an explanation (Jerry or 36 sedan may have added info or a different process) - https://www.youtube.com/watch?v=WHli-wLy9_o

    Here's a tester from Summit, but note you can find them on Amazon, e-Bay or other with widely varying prices - https://www.summitracing.com/parts/w...kaAsF4EALw_wcB

    Quote Originally Posted by NegativeZero
    A pressure gauge on the oil filler tube sounds like an interesting idea, definitely going to try to rig that up.
    LOL just a crazy idea, looking for hard data. I'm not sure how you're going to keep it in place at >6K, but it'll be interesting!
    Last edited by rspears; 12-15-2020 at 09:54 AM.
    Roger
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  13. #13
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    Quote Originally Posted by NegativeZero View Post
    A pressure gauge on the oil filler tube sounds like an interesting idea, definitely going to try to rig that up.

    I wish this was just a case of me using crappy gaskets, but I've replaced my oil pan gasket, timing cover gasket, and the RVT below the intake now and it works great for anything 5000rpm and below, but as soon as I hit 6k+, oil manages to start seeping out somewhere.


    Many moons ago, 1964 to be exact, my dad bought me a 57 Ford when I returned from Okinawa. At the time Ca. was just starting their smog BS and since it was a used car it had to be smog equipped. Everything seemed fine until one evening heading to Anaheim from Santa Fe Springs the crankcase pressure blew the dipstick out, put a dent in the hood, and covered the right side of the windshield in oil. It was some 2 quarts or so low, but after that the oil pressure went south as did the bearings.
    Conclusion: Your money and your engine but I would heed the advice of others and tear it down and start over before it blows up in your face.
    NegativeZero likes this.
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  14. #14
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    The only reason I am hesitant to do that is because I don't know what I would change. The rings are gapped where I want them to be. I don't have the money for new pistons and a larger bore. I feel tearing it down and rebuilding it wouldn't accomplish anything. This is why my original question is about additional things I can do to keep crankcase pressure down. I've been doing research extensively, and I've seen people mention such devices but I was hoping to hear from people with opinions on them.

    I appreciate the advice, I really do, but I'm confident the engine was built correctly. I'm aware that my combination has additional blow-by from the extra ring gap, but in order to run boost, like I'm planning to, I was instructed by various sources to add that gap.

  15. #15
    NegativeZero is offline CHR Member Visit my Photo Gallery
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    I'll definitely be purchasing one of these devices in the near future.

    As for the pressure gauge, I'll hold it on with my hand if I have to. I'm all down for hard data over sitting here and speculating all day on the computer.

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