Excessive Blow-by on Fresh Engine

Discussion in 'Engine Topic' started by 71smalbloc, Jun 24, 2019.

  1. 71smalbloc

    71smalbloc Member

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    Recently had my 350 rebuilt with all new bottom end, Brodix heads and Comp flat-tappet. I've put about 600 miles on the motor since the rebuild and I'm noticing a lot of blow by out of the valve covers (you can see it puff with the breather removed). Besides this the motor runs strong, has good oil pressure and sounds healthy. My engine builder claims it's fine and that this amount of blow-by is normal. Is he right? Or is it just an excuse for him not to take it back apart? Thoughts?



    Thanks,

    Ian
     
  2. COPO

    COPO Veteran Member Lifetime Gold Member

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    How do you see that when you should have a PCV valve on the drivers side cover and a return tube on the pass side going into the breather. Are you running with open holes? If it's getting past the rubber cover hole seals with the PCV installed and pipe to breather then that's not normal. If it is then your oil dip stick should be lifting also.
     
    Last edited: Jun 24, 2019
  3. 71smalbloc

    71smalbloc Member

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    I have that exact setup...I said with the breather removed. Not sure why you're assuming open holes.
     
  4. tom3

    tom3 Veteran Member

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    Was the engine bored out? How far?
     
  5. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Sounds like for whatever reason the rings have never seated. Moly rings will seat pretty quick if the hone finish was correct and the bores were round.
    Best guess is to do a leak down test to see if it’s all the cylinders of one in particular.
     
  6. 71smalbloc

    71smalbloc Member

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    Could be. Builder swears by Total Seal gap-less rings.
     
  7. 71smalbloc

    71smalbloc Member

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    It's 30 over but wasn't bored before the rebuild. Engine builder said it didn't need to be.
     
  8. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Have you had any detonation problems? Might have cracked some rings.
     
  9. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Even if not bored it needed a hone run through it to get the correct bore finish to seat the rings.
     
  10. czizza

    czizza Veteran Member

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    From what I know a piston rings seals whether the piston moves up or moves down so when the pistons are moving down they are also pushing air into the crank case when they are moving up they are pulling air into the crank case. So the blow by you are seeing might be just air displacement.

    I would do a compression test followed by a leak down test. I always do a compression test on a new motor just to see if we are even on cylinders. Once you verified that then do the leak down to see if you have blow by.
     
    71smalbloc likes this.

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