Need advice cylinder scratches

Small Block Mopar Engine

  1. A408Cuda

    A408Cuda FABO Gold Member FABO Gold Member

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    Ok so ill try to keep this short, Ive been building this old Cuda for about 5 years now and I'm almost ready to fire it up. I had this 408 LA built about a year ago, I had to swap oil pans because the Moroso It came with sat to low to the ground. when I pulled the pan I could visually see up and down scratch marks in cylinders 3,5 and 4. I couldn't really feel the marks with my finger but they were there, Unfortunately I didn't have the for-site to take pictures. The engine was only run for the dyno and I was pleased with those numbers. (I didn't see it run.)
    After much digging around the site I've come to the conclusion that there probably from the builder failing to clean up the ends of the rings (debur). At the time I told myself it would be fine and just to run it and see how it goes. But I cant seem to get it out of my head! Is it something i should fix before I start it up. I know what everyone is going to say. Send it back to the builder, but logistically that's a nightmare for me and I'm not sure I'm willing to wait another 6 or 7 months for them to get to it and its a couple states away. So the question should I go ahead and run it and see how it goes? What damage do I risk by running it? Would the smartest thing be to just tear it down now? 408, fully forged, KB pistons, 10 to 1 CR, eddy heads, Howards cam.
     
  2. brian6pac

    brian6pac Well-Known Member

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    Did it ever run hot (over heat) ?
     
  3. A408Cuda

    A408Cuda FABO Gold Member FABO Gold Member

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    No I haven't run it at all havent even started it yet, it was only run once on the dyno at the engine builder.
     
  4. brian6pac

    brian6pac Well-Known Member

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    I would take some good pictures of them and send them to the engine builder just for proof and see what he says.
     
  5. A408Cuda

    A408Cuda FABO Gold Member FABO Gold Member

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    Ya I'm kicking myself for not taking pictures when I had the pan off, now the motor is in and I need to pull it again to take the pan off. Big job everything is such a tight fit in this thing. At the time I just didn't think to much of it. :mad::BangHead::BangHead:
     
  6. brian6pac

    brian6pac Well-Known Member

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    Live and learn, we've all been there one time or another. Drive it and hope for the best, It will probably be fine.

    It has run in for at least 30 min, cam is broke in and the oil has been changed.
     
    Last edited: Mar 14, 2019
  7. A408Cuda

    A408Cuda FABO Gold Member FABO Gold Member

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    I'm going to e-mail the builder and see what they have to say about it, i really don't want to miss another summer but it is what it is I guess. I was really hoping someone had has similar experience and would tell me not to worry about it, but realistically i should pull it apart.
     
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    • brian6pac

      brian6pac Well-Known Member

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      I had a friend that had a sbc that was over heated during breakin and the rings bottomed out and made marks in the cyl walls, they looked deep but you could barely feel them with your finger nail. I told him to rehone it and replace the rings and basically look it over good, the heads were already off for a head gasket leaking coolant, he said he wanted it running and he would pull it down next winter. He is still running it with no problems. The damage is done so run it and fix it next winter if it burns oil or if you get lucky it might just be fine.
       
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      • Rocket

        Rocket FABO Gold Member FABO Gold Member

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        Yo may be able to use a scope that attaches to your phone and run the probe up the oil pan drain plug to see if you can get pictures that way. From the top side you can Look inside the cylinders by going down through the spark plug holes. You may have to use a power bar to turn the crank bolt to seee all the walls.
         
      • RustyRatRod

        RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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        Then don't worry about it. That's what you said you wanted to hear.

        I mean.....you've already said it would be in the back of your mind. I guess the question you should ask yourself is, do you want to get it running now and have to pull it later or do you want to pull it now and make sure it's ok?
         
      • Demonic

        Demonic Well-Known Member

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        If they're that small, you can't catch a fingernail - I wouldn't worry about it. If you don't trust your engine builder to deburr the end gaps properly, you might have good reason to disassemble. As fresh as it is, I might consider tearing it down in place and hand honing it, reassemble with new rings properly gaped.
         
      • nm9stheham

        nm9stheham Well-Known Member

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        That small.... run it and don't think about it anymore....seriously. Any engine is going to get tiny scores and scratches in the cylinders in the normal course of operation; I have never pulled an engine apart without finding such marks in the cylinders.

        I would not worry 1 microsecond over this and would take it racing in a heartbeat and IMHO any work on this would be a total waste of $$ and effort. I may have deburred the ring ends once in my life LOL.
         
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        • brian6pac

          brian6pac Well-Known Member

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          Have you ever taken a 100,000 mile engine apart that was running good, not a new style but a 70's 80's engine and seen how badly worn they are and you think how did this thing ever run?
           
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          • A408Cuda

            A408Cuda FABO Gold Member FABO Gold Member

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            Really my concern with the scratching is the short time it ran i wouldn't think would be enough to cause that. Second it makes me think the rings will never seat properly, the dyno sheets say just shy of 500 hp not sure how that can be correct if the rings are F-ed on three cylinders. I have pulled high mileage motors and seen this, I've also pulled high mileage motors that still had a crosshatch.
             
          • brian6pac

            brian6pac Well-Known Member

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            Are you sure the marks are from the rings and not the piston skirt? how far down are the marks on the wall, all the way to the bottom, 3" from the bottom?
             
          • MopaR&D

            MopaR&D Nerd Member FABO Gold Member

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            I didn't deburr the rings when I built my last 360. I think the cylinders had a little bit of scratches? Can't say what it was from though I put 25k miles on that thing and it never had much blowby or indication the rings/bores were worn.

            The part of the cylinders below the bottom of the piston ring's travel often looks weird because it doesn't have anything wearing on it; are these scratches near the bottom of the cylinders not more than 2" up? If so they are a non-issue because the rings will never touch that part of the cylinder anyway.
             
          • nm9stheham

            nm9stheham Well-Known Member

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            Is there any particular relationship between running time and scratches.....??

            The scratches have nothing to do with ring seating. Ring seal does not get effected by tiny vertical scratches. Just for grins... here's a couple of leakage paths:
            • 10 scratches that are .002" wide by .001" deep. Total area .00002 square inches
            • Typical ring gap when hot: .010" by .020". Total area of .0002 square inches.
            So the ring gap area is 10 time bigger than 10 scratches..... and we are not counting other factors. I think your conclusion on the power not being effected is shown by this.
             
          • nm9stheham

            nm9stheham Well-Known Member

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            BTW, OP.. .best thing to do IMHO to put your mind at ease: Run a leakdown test. Make sure the pistons are on an upstroke for each cylinder's test (to simulate ring position with cylinder pressure).
             
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            • A408Cuda

              A408Cuda FABO Gold Member FABO Gold Member

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              No not all the way to the bottom I'm pretty certain it matches the location of the rings.
               
            • A408Cuda

              A408Cuda FABO Gold Member FABO Gold Member

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              I haven't run it yet the only run time is on the dyno at the engine builder so i don't know how long they ran it for. I'm reluctant to try a leak down yet its been sitting for about a year since the build I would like to run it for awhile first then do a leak down if i feel like its not correct. I'm really just concerned if there some greater risk in running it as is. If there something wrong I will have to tear it down anyway, I just don't want to cause more damage as in ruin the bore or pistons.
               
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              • A408Cuda

                A408Cuda FABO Gold Member FABO Gold Member

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                So I talked to the engine builder and they said probably nothing to worry about but get them pictures. I try and run a bore camera down the spark plug holes when i get home in a week or so. Ill post them. Thanks all for speaking up I really appreciate the advice and expertise on this site.
                 
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