327 350HP Oil Leak - NCRS Discussion Boards

327 350HP Oil Leak

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  • Daniel E.
    Very Frequent User
    • April 30, 2005
    • 145

    327 350HP Oil Leak

    I'm hoping someone can help.... I recently finished the frame-off of my car (@250 miles) and have been chasing an oil leak since the first drive. The leak is at the back of the motor between the oil pan and the flywheel shield. The leak leaves four to five streams of oil down the center outside of the flywheel shield and a puddle on the ground about 3 inches in diameter. The oil doesn't leak when the car is first started and allowed to sit at an idle (10-15 minutes). It seems to only leak during and after driving.

    I placed dye in the oil and used a black light to try and pin point it. I did find a leak from the plug that is partially under the back of the drivers side head. The machine shop the did the motor work fixed this problem after I disassemble the top end of the motor. The top of the motor is now dry ( rear breather, valve cover gaskets, intake, oil sending fitting, plug under head), but the leak below still exists.

    Upon further investigation, it appeared my leak was the multi-piece pan gasket behind the starter so I replaced it with the recommend one-piece (info from the discussion board) but still no luck fixing the leak.

    I started thinking, the machine shop screwed me once with the plug under the drivers side head maybe they didn't tighten the oil galley plugs behind the flywheel, so I removed the transmission. The plugs are damp but no significant source of oil.

    Does anyone have any ideas? Is it possible for a rear main seal to leak without saturating the inside of the bellhousing with oil? I am open to suggestions.

    Thanks and sorry for the long post
    Daniel
  • Joe L.
    Beyond Control Poster
    • February 1, 1988
    • 43221

    #2
    Re: 327 350HP Oil Leak

    Originally posted by Daniel Edmond (43962)
    I'm hoping someone can help.... I recently finished the frame-off of my car (@250 miles) and have been chasing an oil leak since the first drive. The leak is at the back of the motor between the oil pan and the flywheel shield. The leak leaves four to five streams of oil down the center outside of the flywheel shield and a puddle on the ground about 3 inches in diameter. The oil doesn't leak when the car is first started and allowed to sit at an idle (10-15 minutes). It seems to only leak during and after driving.

    I placed dye in the oil and used a black light to try and pin point it. I did find a leak from the plug that is partially under the back of the drivers side head. The machine shop the did the motor work fixed this problem after I disassemble the top end of the motor. The top of the motor is now dry ( rear breather, valve cover gaskets, intake, oil sending fitting, plug under head), but the leak below still exists.

    Upon further investigation, it appeared my leak was the multi-piece pan gasket behind the starter so I replaced it with the recommend one-piece (info from the discussion board) but still no luck fixing the leak.

    I started thinking, the machine shop screwed me once with the plug under the drivers side head maybe they didn't tighten the oil galley plugs behind the flywheel, so I removed the transmission. The plugs are damp but no significant source of oil.

    Does anyone have any ideas? Is it possible for a rear main seal to leak without saturating the inside of the bellhousing with oil? I am open to suggestions.

    Thanks and sorry for the long post
    Daniel
    Daniel-----

    I think it's a problem with the rear main seal. In fact, I think you should have looked to that first instead of getting involved in all the other areas. Replacing the rear main seal is not a big deal, at all. Plus, you could have changed the oil pan gasket at the same time. Use rear main seal GM #10121044 or Fel-Pro #2912.

    Just for the heck of it, you might also be wise to check the valve cover gaskets first. Sometimes, these will leak in unseen ways and the oil will find its way to the lowest point. However, given what you've already done, you might have eliminated this possibility already.

    One more thing: when you replace the rear main seal, DO NOT forget to apply sealer to the areas of the block and cap as clearly and definitively described and diagrammed in the Chevrolet Service Manual. This is a MUST. If you find there was no sealer used there in the first place, then you know why your engine leaked.
    Last edited by Joe L.; August 7, 2008, 07:43 PM. Reason: Add Last Paragraph
    In Appreciation of John Hinckley

    Comment

    • Daniel E.
      Very Frequent User
      • April 30, 2005
      • 145

      #3
      Re: 327 350HP Oil Leak

      Thanks for the information! I will try to locate a Felpro 2912 at one of my local autoparts store tomorrow.

      Do you know if the Felpro 1885 one-peace pan gasket is reusable?

      Daniel

      Comment

      • Joe L.
        Beyond Control Poster
        • February 1, 1988
        • 43221

        #4
        Re: 327 350HP Oil Leak

        Originally posted by Daniel Edmond (43962)
        Thanks for the information! I will try to locate a Felpro 2912 at one of my local autoparts store tomorrow.

        Do you know if the Felpro 1885 one-peace pan gasket is reusable?

        Daniel
        Daniel-----


        Yes, the one piece pan gaskets are generally re-usable. However, inspect it carefully for any problems before re-using. If you detect any significant problems, the best plan is to replace it.
        In Appreciation of John Hinckley

        Comment

        • David H.
          Frequent User
          • October 25, 2006
          • 92

          #5
          Re: 327 350HP Oil Leak

          Daniel,

          I just finished that same job. I had a persistant leak in the corner of the oil pan rail beneath the starter while engine running. I had replaced two oil pan gaskets (one piece FelPros)- still leaked. I bought a FelPro 2912 rear main seal, took everything apart, no apparent oil leak thru the seal onto the flywheel behind the cover. There didn't appear to be enough sealer on the bearing yoke cover where it meets the block - and I think that is where my leak was - leaking thru that interface and onto my oil pan gasket making it appear the leak was at my gasket. I cranked it this evening and everything looks good - just had one tiny drip every 5 -10 minutes after getting to operating temp. and I can live with that. Good luck.
          Dave
          David Hobby (46447)

          Comment

          • Ray G.
            Extremely Frequent Poster
            • May 31, 1986
            • 1189

            #6
            Re: 327 350HP Oil Leak

            Hello;

            Made a living in '65 on 350 HP 327s oil leaks.

            Most eventually turned out to be line bore(which Chevrolet would not pay for at the time). Their solution was to replace engine blocks w/ fitted blocks. Chevrolets claimed that they would not pay an independent shop to line bore a block.
            I thinking any engine man worth his salt would check line bore before proceeding.
            If the line bore in out of specs. the crankshaft has excessive clearance on the top or bottom bearing shell causing a leak

            Just my 2 cents
            Ray
            And when you get the choice to sit it out or dance
            I hope you dance


            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15672

              #7
              Re: 327 350HP Oil Leak

              I think a lot of leaks get blamed on rear crankshaft seals without justification.

              If the rear crankshaft seals leaks there will definitely be oil on the front face of the flywheel. If the front face of the flywheel is dry, it's another source, and I think properly sealing the rear main bearing cap/block mating surface is often overlooked as a common leak source. A leak here will not wet the flywheel but will cause a drip from the inspection cover or the corners of the pain rail.

              Duke

              Comment

              • Joe L.
                Beyond Control Poster
                • February 1, 1988
                • 43221

                #8
                Re: 327 350HP Oil Leak

                Originally posted by Duke Williams (22045)
                I think a lot of leaks get blamed on rear crankshaft seals without justification.

                If the rear crankshaft seals leaks there will definitely be oil on the front face of the flywheel. If the front face of the flywheel is dry, it's another source, and I think properly sealing the rear main bearing cap/block mating surface is often overlooked as a common leak source. A leak here will not wet the flywheel but will cause a drip from the inspection cover or the corners of the pain rail.

                Duke
                Duke-----


                Yes, the failure to properly seal the block-to-main cap surface may well be the cause of many of the leaks attributed to the rear main seal, per se. However, if one is going in to re-seal this area, one might just as well replace the rear main seal, too. There's no point in assuming that the re-seal will fix the leak without the need to replace the rear seal, itself. Plus, the ends of the seal are factory-treated treated with a special glue. Once the cap is removed the glued interface is disrupted and it's a "crap-shoot" if it will properly bond again.
                In Appreciation of John Hinckley

                Comment

                • Duke W.
                  Beyond Control Poster
                  • January 1, 1993
                  • 15672

                  #9
                  Re: 327 350HP Oil Leak

                  Yup, I agree! If the rear bearing cap is removed for any reason, a new seal should be installed even if the existing seal does not apparently leak - for the reasons you stated.

                  FWIW my Cosworth Vega has a pesky leak in this area. On the deep skirt Vega block the rear cap forms the rear face of the block, and the rear pan rail bolts to the bottom of the rear bearing cap, which must be sealed at both the mating surface adjacent to the cap bolts, AND the sides. The rear bearing cap has machined cavities along the sides for the sealer.

                  GM formerly sold a "kit" consisting of what I recall was a two part sealer that had to be mixed along with a disposable "syringe" to inject the sealer into the side cavities.

                  A lot of CV owners have a simliar leak and blame it on the rear crankshaft seal. The front face of my flywheel is absolutely bone dry, and I am convinced that the leak is either the base or the sides of the main bearing cap, not the rear crankshaft seal.

                  Corvette V-8s are not subject to the leak along the sides, but a main bearing/block interface leak is easily possible if this area was not sealed as clearly stated in all GM service literature.

                  Duke

                  Comment

                  • Ken A.
                    Very Frequent User
                    • July 31, 1986
                    • 929

                    #10
                    Re: 327 350HP Oil Leak

                    Are you using a synthetic oil? That's a guaranteed leak.

                    Comment

                    • Duke W.
                      Beyond Control Poster
                      • January 1, 1993
                      • 15672

                      #11
                      Re: 327 350HP Oil Leak

                      "Guaranteed leak" is an overstatement. If the engine has not been rebuilt in the last 20 years, older seal materials may have more propensity to leak, but newer seal materials should not.

                      On the other hand, there is absolutely no need to use "synthetic" oil in a vintage Corvette unless you drive more than 7500 miles between changes or do cold starts consisently below 10-15 deg. F, and the type of "synthetic" you should use is 5W-40 CJ-4. Any other "synthetic" viscosity range is likely SM and not a wise choice for vintage engines.

                      Duke

                      Comment

                      • Daniel E.
                        Very Frequent User
                        • April 30, 2005
                        • 145

                        #12
                        Re: 327 350HP Oil Leak

                        Thanks everyone for your help!

                        Yesterday, I reinstalled the tranny, pulled the pan and replaced the rear main seal (Felpro 2912). After a short 3-4 mile drive, everything is dry. I'm keeping my fingers crossed.

                        I have been using Rotella 10W-30 oil, no synthetic here.

                        Daniel

                        Comment

                        • David H.
                          Frequent User
                          • October 25, 2006
                          • 92

                          #13
                          Re: 327 350HP Oil Leak

                          Joe,

                          I've attached the instructions for installing the rear main seal from Fel-Pro. I had read a previous post by you about not putting sealant on the ends of the seal, but was a bit confused when I read their instructions. They appear recommending putting sealant there. These instructions were included with the 2912 (also scanned instructions for oil pan gasket).

                          Have they quit putting factory treated sealant on the ends?

                          Thanks,
                          David

                          Originally posted by Joe Lucia (12484)
                          Duke-----


                          Yes, the failure to properly seal the block-to-main cap surface may well be the cause of many of the leaks attributed to the rear main seal, per se. However, if one is going in to re-seal this area, one might just as well replace the rear main seal, too. There's no point in assuming that the re-seal will fix the leak without the need to replace the rear seal, itself. Plus, the ends of the seal are factory-treated treated with a special glue. Once the cap is removed the glued interface is disrupted and it's a "crap-shoot" if it will properly bond again.
                          Attached Files
                          David Hobby (46447)

                          Comment

                          • Joe L.
                            Beyond Control Poster
                            • February 1, 1988
                            • 43221

                            #14
                            Re: 327 350HP Oil Leak

                            Originally posted by David Hobby (46447)
                            Joe,

                            I've attached the instructions for installing the rear main seal from Fel-Pro. I had read a previous post by you about not putting sealant on the ends of the seal, but was a bit confused when I read their instructions. They appear recommending putting sealant there. These instructions were included with the 2912 (also scanned instructions for oil pan gasket).

                            Have they quit putting factory treated sealant on the ends?

                            Thanks,
                            David
                            David-----


                            Yes, that's a new instruction and that's probably why they have it blocked in red. Apparently, the seal ends are no longer treated with glue. I don't know if this is also true of the GM seals. The last one of those I used had instructions not to get anything on the seal ends. It's possible those have changed, too.
                            In Appreciation of John Hinckley

                            Comment

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