Intermittent crankcase pressure issues

Small Block Mopar Engine

  1. T56MaxTorq

    T56MaxTorq Well-Known Member

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    I agree with AJ, the heads are flooding. Do you have a baffle In the valve cover to shed some of that oil?

    On a whim, have you looked at the rocker shafts thoroughly? You beat the shit out of them with that mistake on their orientation. Could they be cracked? The end caps dislodged? Are they even positively seated correctly now? You said the condition improved after correcting the rocker shafts, that’s a good thing and a sign of the original problem. Could it just be residual oil at this point? A soaked breather is going to have a lot of residual oil that will heat up and leak over everything.

    I too have crankcase pressures that are high - it’s the turbos fault with loose tolerances. I run plumbing to an oil separator and drain it off.
     
  2. Deceus

    Deceus Well-Known Member

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    Because the engine isn't spinning at 5000 rpm during the tests lol. You're 100% sold on the rings being the issue, got it.

    I only bent a few pushrods. The shaft seemed to seat pretty good and didn't have anything obviously wrong. I did everything but pull the heads and valves back in February. I put a new breather on in case the other one was too restrictive as well and it's coming from more than just the breather so it's not residual.

    47146758_10156916021056810_1465426584943984640_o.jpg?_nc_cat=102&_nc_ht=scontent.fric1-1.jpg

    Cylinder walls all look flawless, couldn't get the heads disassembled with the valve spring compressor I have so they're going to machine shop tomorrow. Kinda bummed I won't get to figure this out myself but chances are they were gonna have to go anyways.

    EDIT: just kidding I ordered a better valve spring compressor from Summit and hopefully I'll be getting to the bottom of this mystery Monday or Tuesday.
     
    Last edited: Nov 30, 2018
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    • famous bob

      famous bob mopar misfit FABO Gold Member

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      I spent a little time yesterday and built a recovery hose and ran it inside the filter area, right beside the throttle body. Had a bunch of "stuff" laying around, came out pretty good. Will address my leaking main stud girdle before testing tho.
       
    • moper

      moper FABO Gold Member FABO Gold Member

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      You're right. And they seal the same way at 0 rpm, 4 rpm, or 7500 if it's working the way it's supposed to. I'm not sold on anything. I'm simply following what your results are telling me based on how an engine actually works. I think that last part is what's being struggled with here.

      Higher rpm can push the top ring off the ring land and lose seal. That's what I'm thinking is the issue. But that's a ring, ring gap, or piston problem. Not a head problem...lol. Check the gap on the top vs 2nd rings. If the top was gapped to be large because of the KB directions, and the 2nd was left at the usual ".004 per inch of bore" deal that's your problem. File the 2nd ring gap to .003" more than the top ring gap and clean the bores and it should be fine.
      But I've been wrong before and I'm sure you'll figure it out.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Mmmmmmm.....I can't agree with you.... the cylinder walls look a bit glazed in the above pix. Notice the very strong reflections of of the cylinder walls? Not sure how much is due to a flash on the camera, but the wall condition looks suspicious.

      Do you know what grit the walls were finished to?
       
    • teringer

      teringer ase master hall of fame FABO Gold Member

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      did you get thin race rings? instead of std ring thickness? for the KB pistons? also is the exhaust cross over in the intake blocked or gasket blew out on intake cross over letting exhaust into engine ,I replaced a 200,000 mile engine that I though was wore out turned out just the intake gasket blew out and let exhaust pressure in engine
       
      Last edited: Nov 30, 2018
    • furrystump

      furrystump Well-Known Member

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      In the first picture of the machined block the cylinders looked polished. Couldn’t see any cross hatch. Ring seal.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      I had not noticed that before..... good observation, FS.
       
    • MopaR&D

      MopaR&D Nerd Member

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      A bit of a ridge is visible too, to the OP can you catch a fingernail on the ridge at the top of the cylinders?

      Not trying to be a d**k but flawless cylinder walls have clear cross-hatching (directional scratches) evenly on their entire surface; worn cylinders are shiny and smooth.
       
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      • Deceus

        Deceus Well-Known Member

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        There definitely was a cross-hatch in the cylinders. You can still see it in area above the ring line. The ridge also isn't really a ridge, I can't feel it at all let alone catch a fingernail. There is some light cross-hatching still visible throughout the cylinder it's just hard to capture on a cell-phone camera.

        g0AqcXZ.jpg
         
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        • Deceus

          Deceus Well-Known Member

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          No idea but these were all taken with a crappy phone camera with a bright flash. When I said "flawless" I meant as in no grooves or marks.
           
        • Deceus

          Deceus Well-Known Member

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          Yeah pulling the pistons out is the next stop for sure. I don't wanna take out the bottom end if I don't have to though. Sucks waiting but I can't say I could use a break at this point. Dealing with headers and the starter is never fun. The bellhousing bolts put up the toughest fight though surprisingly.

          The intake gasket looked new and was still whole.

          Keith Black KB Performance Piston Ring Sets 3910BD8-030

          These are the piston rings I used. They came pre-gapped to their suggest standard and we double checked each one as they went into the engine. Not planning on running boost or NOS so I didn't need to file them down.
           
          Last edited: Nov 30, 2018
        • nm9stheham

          nm9stheham Well-Known Member

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          Pretty good pix now actually. Hmmmmm #2..... something is not right here IMHO. With what are fairly low miles? I do see some crosshatch left, but such a distinct ridge at the top should not be there with limited miles. Cross hatch angle seems OK. More perplexing are the radial grooves going around the cylinder walls.... those should not be there at all.

          Looks like teringer may have nailed it if you used that ring pack PN... those rings are 1/16" tall rings for 1st and 2nd rings.... the standard KB167 call for 5/64" tall rings. PN 3910AM8-xx. Short rings won't seal.
           
        • JFLN

          JFLN Well-Known Member

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          Actually the pcv valve is almost fully closed at idle and high vacuum. The pcv valve is fully open and functioning at wot. When you did your leak down test did you listen at the exhaust, intake, valve covers, and dip stick tube to see where the air was leaking to? If you redid your pcv system did you use oil resistant vacuum hose? Fuel line hose is for pressure and will collapse under vacuum witch is how the pcv system works. Also make sure the pcv valve is sealed to the grommet and the grommet sealed to the valve cover good.
           
        • nm9stheham

          nm9stheham Well-Known Member

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          One you get a piston out, any short rings will be obvious. The ring side clearance (between ring and groove) is normally in the .004"-.006" range; you insert a feeler gauge between the groove and ring to measure this. With rings that are 1/64" short, the ring side clearance will be .019" or more; .010-015" side clearance is what you will find in a worn engine'e pistons/rings. With excess side clearance, the rings will twist up and down in the bore, round the ring faces, etc.

          If this turns out to be the situation, then check the grooves in the pistons for being worn/damaged. You should check them with a new-thickness ring to see if the grooves have been worn/damaged too wide to meet new rings side clearance specs. If the grooves worn/damaged, then you will be back to a similar situation. Either replace the pistons, or see if there is a shop locally that can widen the piston grooves enough to use what is know as a ring spacer, or use wider rings if available. Re-grooving and using spacers an old-time method to salvage used pistons; not sure how well it would work with KB's, or if it is really cost-effective here.

          IMHO, if there is no ridge in the cylinders, then you might get away with a fresh cylinder hone. But what appear to be shallow radial grooves around the bore in the above pix, is concerning... if they are real, and remain after a light hone, then that is not going to do new rings any good; ring wear will likely be more rapid than normal.
           
          Last edited: Dec 1, 2018
        • teringer

          teringer ase master hall of fame FABO Gold Member

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          look at the scratches in the wall looks like the rings were too tight and not enough clearance
           
        • teringer

          teringer ase master hall of fame FABO Gold Member

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          alright this has to be said you need to start all over pulling the engine and taking it back to the machine shop and have it re honed the cylinders wont reseal unless they are round the rings you used are wrong and because you didn't file fit them to the cylinders they are not round it shows where they were butting together from no ring gap clearance .never saw a set of rings for kb pistons fit out of the box had to fit them all .you need at lease .024 gap when using kb pistons.
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          I had to take my street-engine down too, for tight rings. I thought the pistons were too tight, and took the bores out another half. I put a new set of file fits in for good measure. One of those or both,cured my problems. PITA but you learn as you go I guess. That was just the first of several tear-downs. I heard that thought! ; yes, maybe I just was a slow-learner,lol. In any case, that was 18 years ago.
           
        • Deceus

          Deceus Well-Known Member

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          Mystery solved then. Definitely think I grabbed those rings when I looked up Keith Black 3.940 rings because I remember the plasma-moly coating and I definitely used KB167s. That would mean I'm running a 1/16" ring in a 5/64" groove.

          I think I'm up to 4-5 dumbass mistakes on this engine build now. At least this one was my own. Might just ditch this block all together and start over with the 360 block I just inherited.
           
        • teringer

          teringer ase master hall of fame FABO Gold Member

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          also just a heads up if you do re hone the block and it takes a few thousands out to fix it. I would switch pistons to a non -hyper type the kb has no offset on the piston pin and will knock with more cylinder clearance you should use a stock type piston with a offset wrist pin they work better and wont knock with wider piston clearance
           
        • nm9stheham

          nm9stheham Well-Known Member

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          Well, stuff happens. As I like to say, if you never make a mistake, you are not trying to do anything. Give yourself at least a pat on the back for figuring something was not right, instead of just running and running.

          KB piston's can be bought kitted with the correct rings BTW. The moly's are a good choice for street engines IMHO.
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          When I first put the Moly file-fits in, the LeakDown was so low it hardly registered on my gauge. I was a bit worried the rings were still too tight! Man-O-man did that engine make torque (223@.050). and she no longer locked up after I shut it off. Win-win said I.
          I think that was early 2004 when those rings went in. I made a lot of changes that winter.
           
        • Cudafever

          Cudafever Well-Known Member

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          Sound like you found the problem.....but i would still like to see the underside of your valve covers......
           
        • Deceus

          Deceus Well-Known Member

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          MwozEHj.jpg
           
        • Cudafever

          Cudafever Well-Known Member

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          yup that looks good.
          Thank for taking the time.
           
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