Damn oil leak, Rear main??

Small Block Mopar Engine

  1. 340Duster247

    340Duster247 Well-Known Member

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    Hey guys, I've had this little small block in and out many times with various combos and rebuilds and along the way I've never had an oil leak that's acted like this one so maybe you could help me out.
    This is bar far the worst oil leak I've had, shut off the engine and got the dreaded drops coming from the back upper of the pan. "f**k I guess the engine had to come out" but before I pulled the engine I figured I would investigate. Seeing how this new engine/combo just went in at the start of summer I'm not really to motivated to yank it.
    Got under the car and cleaned up everything removing any oil mess since this leak happens to get onto the flex plate and spatter everywhere.
    With it all clean, I start the car and wait and look. Nothing. Dry. Zero leaks. Let the car idle and get up to temp. After 30 mins of run time I rev the engine a couple times. Under the car still nothing. Dry.
    I shut the engine down, get under the car and it instantly starts coming out at a pretty good pace.
    Hmmmm, rear main seal???
    Anyone had a similar leak.
    I think I have an idea what's going on , but want to get the wisdom from you guys first. Lol
    Added a photo of the leak and new combo for ya guys too.

    IMG_20201017_120006.jpg

    IMG_20200928_085647.jpg
     
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    • cawcislo

      cawcislo Well-Known Member

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      Would pulling the trans help verify the leak and could you do the repair without pulling the whole motor out? If it is the rear main - Do you have enough clearance to pull the oil pan if needed by lifting the engine a couple inches?

      PS the turbo looks killer.
       
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      • 340Duster247

        340Duster247 Well-Known Member

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        Well what's great is no headers. So I have more room then normal. I was thinking about pulling the trans back (or out completely to take a look) I've yanked that trans more then couple times ... Ughhh bit of a night mare with just a couple floor jacks, but might be an option.
         
      • abdywgn

        abdywgn dismantler

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        cam plug? mine would leave the puddle on shut down...who knows how much was sprayed while driving. the later Magnum style would be the one to use instead of the earlier welch(?) plug.
         
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        • MarPar

          MarPar If it weighs, it pays FABO Gold Member

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          img_20200928_085647-jpg.jpg

          jaw hitting floor.gif
           
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          • DFX 340 Duster

            DFX 340 Duster FABO Gold Member FABO Gold Member

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            Just pull the engine and tranny and replace the rear main seal. Add another turbo while you have the engine out of the car.
             
          • Mike69cuda

            Mike69cuda 64 is the new 17 FABO Gold Member

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            I replaced my rear main without removing the engine or trans. Most of the work is dropping the steering. After you get the pan off it is easy.
             
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            • AJ/FormS

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

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              When you get the seal out; inspect it very carefully.
              I had my block line-honed, and within a couple of hundred miles I had a leak. I said to myself "hunh" and simply replaced it. A couple more hundred and the leak shows up again. Now I'm pissed cuz I know I did everything I could to make sure it wouldn't leak.
              So I went and dug up the first leaker, and lo and behold, the reason for the leak was right there staring me in the face. The lower half was heavily worn, and the upper had no visible wear.
              So I deduced that during the line-hone, somebody got a little carried away..... and the main-cap was forcing the upper half up and off the crank.
              So I pulled the second seal, and it looked the same.
              So I went and bought a rope-seal off a 383, and fit it into there, badaBoom.

              So I took the seals to the machine-shop that did the work. The shop that just decked this block, and fresh-honed the cylinders.
              You won't believe what the manager said.
              He said that if I would supply another block, they would give it a line-hone no charge. but
              I would have to pay for the decking and the boring and the honing.
              You're kidding I said, among other words.
              Needless to say, the rope seal has been seeping ever since, but not enough for me to do anything about.
              And I never recommend that shop.I don't diss them, I just don't recommend them.
               
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              • 66jim

                66jim Well-Known Member

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                Oil funnels down to the low spot where you see it and may appear as a real main seal leak. It can also be the distributor O ring or gasket, the oil sending unit, the China rail, the oil filter gasket, valve cover gaskets and even the fuel pump and timing cover towards the front. When driven air pushes the leak back and it all drips from
                the low spot. Take it from someone who has gotten fooled.
                 
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                • 340Duster247

                  340Duster247 Well-Known Member

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                  Well boys I got motivated and pulled the trans so I could see behind and maybe get a better idea..well there too much spatter to tell. It looks like some of the plugs could be leaking but it's too hard to tell. I also can't tell if it's where the oil pan meets below the crank, or the main seal it's self.
                  F**k I hate leaks. Ughh.
                  I didn't mine pulling the tranny as I'll be installing a cope valve body and trans brake this winter.
                   
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                  • Divenut

                    Divenut Well-Known Member

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                    Is that the CRT RMVB with the low band apply?
                     
                  • 340Duster247

                    340Duster247 Well-Known Member

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                    It will be yes.
                     
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                    • Divenut

                      Divenut Well-Known Member

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                      Nice. Seens like a very nice piece. I hope to hope to replace my current Cheetah RMVB w/o low band apply unit with the CRT unit.

                      Be well,
                      Pat
                       
                    • famous bob

                      famous bob mopar misfit

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                      • George Jets

                        George Jets 1967 Dart 2 Door FABO Gold Member

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                        I have lately been wondeing about those rear main seals.

                        There is the earlier rope seal and the angled knurling on the crank seal area. I can see how this works with the engine running winding the oil back into the engine with the knurling. With the engine sitting off, can the oil seep back through the knurling?

                        Then on a rebuild or newer lip seal rear main seal. The new lip seal sitting on the knurling, with it running pushes the oil back into the engine.

                        With the engine stopped the new lip seal would be bridging the knurling peaks and allowing oil to run back out throgh the knurling valleys ??

                        So my question is with the lip seal style rear main seal, would it be a good idea to polish down the knurling smooth so the rear main lip seal has a smooth surface for the lip to seal against.

                        Just like the smooth surface seal up on the front harmonic balancer and timing cover.

                        Also wondering if the aftermarket cranks and stroker cranks have eliminated the knurling altogether ???

                        Maybe even the stock reman cranks have the knurling removed as part if their reman process ??

                        Granted you want a good vented crank case and PCV setup to eliminate any positive crank case pressure pushing the oil out.

                        Any thoughts or opinions on this ???
                         
                      • AJ/FormS

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

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                        To pinpoint the leak just seal the engine, and then pressurize the CC to 3 psi/ not more than 4psi, and then hit it with soapy water.
                        To seal the engine, I flip out the PCV, and plug the hole, same at the breather. Then I pressurize thru the dipstick tube.
                         
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                        • cawcislo

                          cawcislo Well-Known Member

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                          Clean up the rear of the block. With the trans out you could also grab an oil priming tool and have someone spin the oil Pump to get oil pressure, pull the spark plugs and rotate the engine to get oil everywhere to see if you can pinpoint the leak. Or maybe even just fire the engine up for a short bit of time...Try it a couple times as it seems like you said the problem shows up when you shut the car off. You may also want to make sure the car/engine is level (or as level as it normally sits when the problem occurs). Good luck.
                           
                        • 340Duster247

                          340Duster247 Well-Known Member

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                          Good stuff. This crank was used is the last setup before I switched to lower compression pistons and had zero issues with the rear. I guess I won't know till the pan comes off.
                          As far as blow by this engine has very minimal if any at all. It also has two -12 lines to the catch cans to allow it to breath.
                          Might have to look into a good PCV system if this continues.
                           
                          Last edited: Oct 18, 2020
                        • furrystump

                          furrystump Well-Known Member

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                          Something that is SO FAR out there I have to mention it. I don’t think it is your problem. I have seen where the pilot hole on an aftermarket crank was drilled to deep and intersected the rod oil galley in the crank. There was a video, he would run the drill and build oil pressure and you could see the oil slowly start coming out of the pilot hole. Have to file that under “the last thing I would check!”
                           
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                          • str12-340

                            str12-340 FABO Gold Member FABO Gold Member

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                            Before you do a lot of work, I'd check that whatever gauge tubing or sending unit you have screwed into the oil pressure tap at the back of the motor (next to the distributor) is not loose. Oil is insidious in that it works its way everywhere once it leaves the motor.
                             
                          • 340Duster247

                            340Duster247 Well-Known Member

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                            Thanks , but I've checked all that. This car uses electric sensors for my Holley software, and all dry up top.
                             
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                            • teringer

                              teringer ase master hall of fame FABO Gold Member

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                              someone makes a bearing kit that pulls oil away from the rear seal on engines with high oil pressure .I had same problem with 360 in my dirt car note only the last main bearing was different it had a groove cut in it
                               
                            • cawcislo

                              cawcislo Well-Known Member

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                              Any update? Did you figure it out?
                               
                            • B3422w5

                              B3422w5 Well-Known Member

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                              If it was me i would buy some dye, put it in the engine, run it, then use a UV light.
                              Makes it 50 times easier to spot the leak. You may not have to pull everything out that way. Very easy to do.
                               
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                              • 340Duster247

                                340Duster247 Well-Known Member

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                                Hey guys here's the update. Trans removed, cleaned everything up. Primed engine to get oil pressure and sure enough it's the rear main. Now I have to decide to yank the engine or try it with engine installed. If it wasn't for all the turbo and exhaust piping I'd yank the engine right away....
                                 
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