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Enlarging a Neoprene Hole

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  • Enlarging a Neoprene Hole

    I have a clutch actuator rod with an OD of .232" that travels @ .500" back and forth through a neoprene seal with a .203" ID, leaving a .029 interference fit.

    In use lube will be 50W motor oil. I polished out he annular grinding rings on the rod which seemed to work at first but two days later I had to pound it out with a hammer.

    Both the rod and seal are new components.

    What's the fix for this?

  • #2
    I'm probably not understanding the scenario correctly, but it sounds like you're saying the problem worsened after the polishing. Maybe the smoothness now permits all lubrication to be wiped away. Does that appear to be the case?
    If so, maybe try roughing up the shaft, and see what happens.
    Last edited by lynnl; 04-27-2022, 05:33 PM.
    Lynn (Huntsville, AL)

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    • #3
      Sounds like the seal is swelling from oil absorption. Neoprene shouldn’t, but sure sounds like it.

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      • #4
        Is this a lip seal with a spring tensioner on the inside? If so I'm thinking that .029 might be way too much interference leading to pressuring the lube out of the seal's contact and it grabbing like you say. Seals are pretty universal. Check on suggested fits for some similar size commercial seals. You're likely looking at the nominal shaft size then look for the ID of the seal in the new and unused state.

        Or is this some other sort of arrangement?

        Either way if the seal hole is too small then I'd say enlarging is not in the cards. It'll be new and proper size seal time. No way you'll open up neoprene and get a non leaking finish. At least not without some equipment and procedure costing WAY more than a new and proper size seal.
        Chilliwack BC, Canada

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        • #5
          Not a car guy so probably I'm not understanding. But if this is sheet material not an O-ring, it can be punched easily and will give a good seal. You can make a punch on the lathe to exactly what you want. Sometimes sharpening the end of a tube and 'drilling' the hole also works.
          Location: Jersey City NJ USA

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          • #6
            I'm probably not understanding the scenario correctly, but it sounds like you're saying the problem worsened after the polishing. Maybe the smoothness now permits all lubrication to be wiped away. Does that appear to be the case?
            If so, maybe try roughing up the shaft, and see what happens.



            It wouldn't even go in all the way before polishing. I had it moving well after, but a couple days later locked up tight. This is a clutch actuator rod on a 1941 Harley Davidson 45 transmission.

            This is part of a complete transmission rebuild during which over 50% of the reproduction parts were so far out of spec they needed to be replaced from alternate sources. I wonder if either the rod or the seal or both are out of spec. The seal was extremely difficult to get into the bore, and will probably need to be cut in pieces to be removed.

            The seal in question is the second from the left in the parts picture, all the rest is behind it in the bore. All the holes are aligned and the rod goes through everything else easily.

            I suppose my primary question is how can the bore be enlarged without ruining it. I'll need to get a new one to try anything, maybe I'll get lucky and it will fit.

            Click image for larger version  Name:	seal parts.jpg Views:	0 Size:	19.6 KB ID:	1998525

            Click image for larger version  Name:	Rod & Seal.jpg Views:	0 Size:	25.9 KB ID:	1998526


            Last edited by Spindle; 04-27-2022, 06:19 PM.

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            • #7
              Originally posted by BCRider View Post
              Is this a lip seal with a spring tensioner on the inside? If so I'm thinking that .029 might be way too much interference leading to pressuring the lube out of the seal's contact and it grabbing like you say. Seals are pretty universal. Check on suggested fits for some similar size commercial seals. You're likely looking at the nominal shaft size then look for the ID of the seal in the new and unused state.

              Or is this some other sort of arrangement?

              Either way if the seal hole is too small then I'd say enlarging is not in the cards. It'll be new and proper size seal time. No way you'll open up neoprene and get a non leaking finish. At least not without some equipment and procedure costing WAY more than a new and proper size seal.

              The picture shows the end of the transmission where the clutch pack will be mounted to the splines, and is intended to prevent oil from migrating through the hollow shaft where the actuator lever is, so no system pressure to be held. No lip or spring, just a disc @ 5/16" thick.
              Last edited by Spindle; 04-27-2022, 07:02 PM.

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              • #8
                rubber like materials WET SAND readily. SiC wet or dry bonded paper on a stick spinning in a drill press etc.. Lots of soapy water. Ten minutes and that hole could be any size you desire.

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                • #9
                  Any reason you can't replace it with a standard lip seal?

                  -js
                  There are no stupid questions. But there are lots of stupid answers. This is the internet.

                  Location: SF Bay Area

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                  • #10
                    From what you have described it sure looks like a rubber swelling issue. It was OK at the beginning, but 2 days later the seal was too tight. It is a classic swelling symptom.

                    Now may we assume that 50W motor oil is a mineral oil? Also how sure you are the seal is made out of Neoprene? There are many Neoprene compounds in use today and in general they are not the best to work with mineral oil. If I could, I would select Viton or Buna-N. Both of them have good resistance to mineral oil, but Viton can tolerate higher service temperatures.

                    I doubt you can enlarge the hole in the original seal, but maybe you can make a new seal from the sheet of the correct rubber material. You can make a steel tube of let's say .250" diameter, bore the inside taper to a sharp edge and use it to drill a hole in rubber. You may have to play with tube diameters to get the right fit to your actuator rod. Use mineral oil or water as a coolant.

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                    • #11
                      The forces acting on the pushrod during use will be pretty large-are you sure that it will stick when the clutch springs and pedal are hooked up?

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                      • #12
                        Originally posted by andywander View Post
                        The forces acting on the pushrod during use will be pretty large-are you sure that it will stick when the clutch springs and pedal are hooked up?
                        If it was not an issue, the OP would not make this post. You would be surprised to learn how much trouble the rubber swelling can produce.

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                        • #13
                          Originally posted by mikey553 View Post

                          If it was not an issue, the OP would not make this post. You would be surprised to learn how much trouble the rubber swelling can produce.
                          Uhh, how do you know that he wouldn't make the post? He never said that he assembled the clutch and tested it that way.

                          And I wouldn't be surprised either way...

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                          • #14
                            Originally posted by CalM View Post
                            rubber like materials WET SAND readily. SiC wet or dry bonded paper on a stick spinning in a drill press etc.. Lots of soapy water. Ten minutes and that hole could be any size you desire.
                            True enough, but the hole won't be round.
                            Southwest Utah

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                            • #15
                              Originally posted by andywander View Post

                              Uhh, how do you know that he wouldn't make the post? He never said that he assembled the clutch and tested it that way.

                              And I wouldn't be surprised either way...
                              Actually he said: "seemed to work at first but two days later I had to pound it out with a hammer". It seems like a good test to me. Let's wait for the OP to respond.

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