Crankcase Pressure

Discussion in 'Fox 5.0 Mustang Tech' started by nothwoods, May 11, 2014.


  1. nothwoods

    nothwoods Member

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    Just wanted to throw this out there before I tear down my motor. I have a t-trim running about 15 psi on a 333ci motor, puts 540 to the wheels, (or used to at least!). Last year it started making lots of pressure in the crankcase, which started with blowing out the oil cap, then got worse where it would blow oil out of the breather, then started burning oil out the exhaust. Still runs great, put it away intending to tear down the motor. Just got it out today and drove it down to my shop, ran great and didn't seem to burn any oil until it was warmed up and I got on it hard a couple times. There's no oil coming out of the blower, I think it either has a burnt piston or rings, is there any simple thing I'm overlooking before I tear it down? PCV seems okay. Thanks for reading!
     
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  2. modulistic

    modulistic Member

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    valve seals in the heads. might be blowing out one or two intake valves, pressurizing the crank case, and then blowing oil in through an exhaust valve seal. I think if you vented a piston or hurt the rings, it would be running pretty bad.
     
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  3. nothwoods

    nothwoods Member

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    Yeah I thought about valve seals, is it common for them to slide up on a blower engine? The fact that it still runs so good is just what's bugging me. I would expect to have a misfire, at least at idle. Thanks for replying Mod.
     
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  4. FoxMustangLvr

    FoxMustangLvr Mustang Master

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    Do a compression test or leak down test to eliminate rings. What kind of crank case ventilation setup are you using?
     
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  5. nothwoods

    nothwoods Member

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    I just have the PCV valve in the stock location and a breather cap on one valve cover. I think I'm going to tear it down anyway and at least change the rings and bearings for piece of mind. It's a great running engine and it's endured a lot of punishment without so much as a hiccup, so I think I'm going to freshen it up anyway so I don't destroy it.
     
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  6. RacEoHolic330

    RacEoHolic330 I like to dress like a pretty girl SN Certified Technician

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    With that much boost, I would be ditching the pcv and run two breather Iines into a catch can. I also agree that you should check compression before you start taking things apart.
     
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  7. FoxMustangLvr

    FoxMustangLvr Mustang Master

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    Yup, vent each valve cover to a catch can. Also, even if you just want to rebuild the bottom end anyway, you should diagnose the problem before you go through it and put it all together and still have the same issue.
     
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  8. nothwoods

    nothwoods Member

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    I'm not familiar with the catch can system, I've seen valve covers that extend the breathers up a few inches. It's actually never given me any trouble up until now, and I put this setup together about 12 years ago.
     
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  9. MikeH686

    MikeH686 Mine is only two inches though.

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    image.jpg image.jpg image.jpg
    This is my setup
     
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  10. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    Mines very similar. Good proven setup
     
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  11. nothwoods

    nothwoods Member

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    That's a nice looking setup. Is it an-10 line?
     
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  12. MikeH686

    MikeH686 Mine is only two inches though.

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    I think so it's 5/8" line
     
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  13. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    Looks like 10an
     
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  14. MikeH686

    MikeH686 Mine is only two inches though.

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    Yeah it is I had to do the conversion haha
     
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  15. nothwoods

    nothwoods Member

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    I'm thinking maybe this could be part of the problem? Had 40 psi on #8, but a little JB Weld and she should be good to go! Looks like the block is okay at least.
     

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  16. FoxMustangLvr

    FoxMustangLvr Mustang Master

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    What is that chunk from? Have you drained your oil to check it for any debris?
     
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  17. nothwoods

    nothwoods Member

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    That's a missing piece of piston! I tore the whole motor down, the only damage I can find is to that one piston and rings. The piston is demolished, it even broke around the oil ring land somehow! Haven't pulled the valves out yet but there is no damage at all to the combustion chamber, even the rod bearing looks fine. Thinking about putting in a set of flat tops and a different cam and going back to N/A.
     
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  18. 7991LXnSHO

    7991LXnSHO Active Member

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    At least the leak down told you where to look. I figured the valve guides were not the problem. But WOW, do you think it went lean and melted the piston edge, or did that chunk somehow make it out past the exhaust valve?
     
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  19. nothwoods

    nothwoods Member

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    I'm wondering if it detonated because the fuel was stale, but if it did I couldn't tell driving it. Looks like it started to melt and then a piece broke off, but its weird because there's no marks on the piston or combustion chamber. The lower ring land on a 331/333 stroker crosses the pin bore, and one side is somehow broken downward toward the pan in that spot, can't figure out why. Only damage seems to be to the one piston.
     
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  20. 89oem

    89oem Active Member

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    good catch for sure...
     
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