Blow-by
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Blow-by

  1. #1
    Senior Member fleetimus's Avatar
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    Default Blow-by

    468 BBC, 13-1, roller.

    Yesterday developed severe blow-by out of the breathers. Did a compression check, #7 60, the rest 170 to 185. Haven't pulled the heads.

    What might I find????

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    ill bet number 7 piston has a hole burned the near the intake valve relief thru the ring pack, i have had a few of bbc chev that that did this when i was trying to mad scientist my own race gas.
    I hope not,but blowby and low comp on one cyl this is my best guess.

    as for the cause the list maybe long,bad or low octane,lean cyl, fuel delivery/supply failure

    please let me know i might have a free spare for ya. good luck

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by fleetimus View Post
    468 BBC, 13-1, roller.

    Yesterday developed severe blow-by out of the breathers. Did a compression check, #7 60, the rest 170 to 185. Haven't pulled the heads.

    What might I find????
    Half of the ring lands in the pan..........Just in time for fall....

    GT
    GT


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    Senior Member Oldsquirt's Avatar
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    Quote Originally Posted by fleetimus View Post
    468 BBC, 13-1, roller.

    Yesterday developed severe blow-by out of the breathers. Did a compression check, #7 60, the rest 170 to 185. Haven't pulled the heads.

    What might I find????
    Borrow a boroscope and look inside before you tear it open.

    From Vinnie's movies you sure gave it a workout yesterday!

  7. #5
    Senior Member Morg's Avatar
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    I would leak it first.

    Let me know if you need to borrow a tester.

    But it sounds like something is a fowl with a piston & or cylinder.
    It is supposed to be hard, if it wasn't hard everyone would do it. The "hard" is what makes it great. - Jimmy Dougan

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    Senior Member repoman's Avatar
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    I had a similar symptom and it turned out i blew a head gasket from the cylinder to the lifter valley.

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    Quote Originally Posted by repoman View Post
    I had a similar symptom and it turned out i blew a head gasket from the cylinder to the lifter valley.
    good post repo. i had a older mark 4 block do that did that on number five, put a reher-morrison add a lug kit and o-ringed the block at the same time went to sce copper gaskets.

    morg has a great idea run a leakdown test and see where the air's going should be quick test.

    went down and looked in the shop and i have a new old stock trw L2307A .060 only have one but it's free if you need it.

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    Senior Member fleetimus's Avatar
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    Thanks for the info and offers. I am not sure when I am going to tear it down. But, I will post what I find.

  11. #9
    Senior Member matt1840's Avatar
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    Quote Originally Posted by fleetimus View Post
    Thanks for the info and offers. I am not sure when I am going to tear it down. But, I will post what I find.
    tim if you need a hand im game.. always good to see ya.

  12. #10
    Senior Member fleetimus's Avatar
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    Didn't do a leak down, but hit #7 with air. Serious air coming out of the exhaust port. Bad valve?, but why would it have major blowby out of the breathers???

    Engine is still in the boat, will be coming out in the next few weeks.

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    Quote Originally Posted by Morg View Post
    I would leak it first.

    Let me know if you need to borrow a tester.

    But it sounds like something is a fowl with a piston & or cylinder.
    No shit. You're learning. Could be just a little piece of carbon on a valve seat. Broken spring, valve lash, etc, etc.

    Leak the whole motor first. Example: Maybe #6 exhaust valve is creaping......while the head is off you can lap the seat. The more you know before you go in there....the better off you are.
    Then take the valve train loose and leak it again. While putting air to #6.....you feel air coming out of #4 plug hole. Look for head gasket sealing problems that way.
    Last edited by Fiat48; 09-27-2009 at 10:06 PM.

  14. #12
    Senior Member Factory1's Avatar
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    Quote Originally Posted by fleetimus View Post
    Didn't do a leak down, but hit #7 with air. Serious air coming out of the exhaust port. Bad valve?, but why would it have major blowby out of the breathers???

    Engine is still in the boat, will be coming out in the next few weeks.
    Did you have the #7 cylinder at TDC on compression stroke when you hit it with the air?

  15. #13
    Senior Member fleetimus's Avatar
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    Blown head gasket into the lifter valley.


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    Yeah. The bolt chevy left out.

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