Hello, Allpar Forums member or visitor! If you were a member, you would not see this ad!

Register or log in at the top right of the page...

  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Excessive crankcase pressure

Discussion in 'Repairs, Maintenance, Help' started by Coopbob, Dec 9, 2017.

  1. Coopbob

    Coopbob New Member

    Joined:
    Dec 9, 2017
    Messages:
    4
    Likes:
    1
    Just restored a slant 6 225 A100 1966 model truck. After about 30 minutes of break in the engine popped super loud, blew off the oil cap, blew out the dipstick, and cause the timing chain cover to distort. The engine still runs but can not figure out what caused this? Has anyone heard of this or know what would cause such a thing?
    Thanks
     
  2. ImperialCrown

    Level III Supporter

    Joined:
    Jun 8, 2008
    Messages:
    18,340
    Likes:
    2,703
    Welcome to Allpar. Is the PCV valve installed and working correctly? The PCV 'rattle' test just makes sure that the internal shuttle valve is free, but can you blow through it one way and not the other?
    The 'pop' may have been a backfire and the intake manifold flame-front travelled through the PCV hose into the crankcase and ignited the blow-by. If the PCV valve was working correctly, it should have stopped flow in the wrong direction, thus not allowing the backfire flame to enter the engine and ignite the blow-by. See the PCV valve position in 'Backfire' here:
    fig0452.gif
    I have seen valve covers torn off from internal crankcase explosions.
     
  3. Coopbob

    Coopbob New Member

    Joined:
    Dec 9, 2017
    Messages:
    4
    Likes:
    1
    Thanks for the reply. This was still running under break in and we did not have a PCV valve in place. that portal to the valve cover was open.
    Thanks
     
  4. ImperialCrown

    Level III Supporter

    Joined:
    Jun 8, 2008
    Messages:
    18,340
    Likes:
    2,703
    Then the blow-by was ignited by another flame source. Possibly an exhaust valve stem/guide flame or piston ring flame?
    You want PCV action to remove the combustible internal fumes in a break-in situation where there may be high amounts of initial blow-by.
     
  5. Coopbob

    Coopbob New Member

    Joined:
    Dec 9, 2017
    Messages:
    4
    Likes:
    1
    But would you not have ventilation if the PCV port at the top of the valve cover was completely open. Which it was.
     
  6. ImperialCrown

    Level III Supporter

    Joined:
    Jun 8, 2008
    Messages:
    18,340
    Likes:
    2,703
    It might be a 'vent', but the PCV would actually scavenge the fumes from the crankcase, which is what you want.
     
  7. Coopbob

    Coopbob New Member

    Joined:
    Dec 9, 2017
    Messages:
    4
    Likes:
    1
    Very Good point. I will get my PCV valve put back in. Thanks for your help
     
    ImperialCrown likes this.
  8. David Eidell

    David Eidell Well-Known Member

    Joined:
    Jan 15, 2010
    Messages:
    232
    Likes:
    25
    May I ask a question about this?
    Does not this system have a "KV Vent" with foam pad in the air filter housing? This would allow another route into the crankcase. This is only a guess and not a critique of your answer...
     
  9. ImperialCrown

    Level III Supporter

    Joined:
    Jun 8, 2008
    Messages:
    18,340
    Likes:
    2,703
    If this 1966 truck has the Chrysler CAP (cleaner air package), the crankcase breather would be the air inlet for crankcase air flow with the PCV providing the vacuum:
    MD904.jpg
    The link in post # 2 ( fig0452.gif ) shows the V8 flow for both the open and closed breather systems. The closed breather is the one you are describing.
    This may be too early for a foam element in the air cleaner and the filtering element may be in the valve cover breather cap.
    A V8 crankcase flow would be along the same idea as a 6-cyl.
     

Share This Page

Loading...