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Oversized Wrist Pins

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  • Oversized Wrist Pins

    Can someone please tell me what the MoCo's thought process for making oversized wrist pins ? It seems that it is much easier to replace the wrist pin bushings and size them than to ream the piston and wrist pin bushing. I have quite a few 45 and Big Twin wrist pins that are oversized.

    Craig

    CIMG1807.jpg

  • #2
    I've never seen bushings in a motorcycle piston. Either I've led a sheltered life, or it's not done . . . Why? I'd be curious to know as well.
    Last edited by exeric; 07-27-2020, 07:24 PM.
    Eric Smith
    AMCA #886

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    • #3
      Originally posted by exeric View Post
      I've never seen bushings in a motorcycle piston. Either I've led a sheltered life, or it's not done . . . Why? I'd be curious to know as well.
      My mistake Eric. I should have said upper rod bushings. They say that the first thing to go on us old farts is the mind. I believe that I'm starting to prove them right !
      Craig

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      • #4
        Originally posted by 41craig View Post
        My mistake Eric. I should have said upper rod bushings. They say that the first thing to go on us old farts is the mind. I believe that I'm starting to prove them right !
        Craig
        I believe Eric's point was to fit the piston to the OS pin, the bushing wasn't the reason for them....
        Robbie Knight Amca #2736

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        • #5
          Robbie; I've not seen a piston that needs an OS pin. I'm still trying to figure out what the need was for an OS pin ? I did find this ( see attachment ) in my old 1970 tech school book.CIMG1813.JPG
          This paragraph does not answer my question.

          Craig

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          • #6
            Originally posted by exeric View Post
            I've never seen bushings in a motorcycle piston. Either I've led a sheltered life, or it's not done . . . Why? I'd be curious to know as well.
            Sorry, that was a weird reply on my part To address your question, Craig; I think H-D was just covering the bases for many eventualities, and for the benefit of the end users. I do see the validity of your question however. I shouldn't respond during cocktail hour
            Eric Smith
            AMCA #886

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            • #7
              Originally posted by 41craig View Post
              Robbie; I've not seen a piston that needs an OS pin. I'm still trying to figure out what the need was for an OS pin ? I did find this ( see attachment ) in my old 1970 tech school book.
              This paragraph does not answer my question.

              Craig
              Thanks for that school note, Craig!

              It is remarkable in that it addresses six decades at least.

              A quick look at a Parts Catalog shows seven sizes of pin 'kits', from .002" to .015" oversize.

              Pistons must have lasted longer back then.

              ....Cotten
              AMCA #776
              Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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              • #8
                It's to avoid replacing the pin bushing.
                The Linkert Book

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                • #9
                  Eric and Kitabel; I guess that if you have reamers and O.S. pins and no way to replace or do not have bushings. Then the O.S. pins are the answer.
                  Tom; You can make a piston last longer if you have a piston knurler. ( See pic ) You can add up .010" to a piston with that machine. Also, sometimes my old machine shop books shed a little light on the subject.CIMG1821.jpg

                  Craig

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                  • #10
                    Originally posted by 41craig View Post
                    Eric and Kitabel; I guess that if you have reamers and O.S. pins and no way to replace or do not have bushings. Then the O.S. pins are the answer.
                    Tom; You can make a piston last longer if you have a piston knurler. ( See pic ) You can add up .010" to a piston with that machine. Also, sometimes my old machine shop books shed a little light on the subject.[ATTACH=CONFIG]29129[/ATTACH]

                    Craig
                    I've found knurled pistons, Craig! (Most were knarled.)

                    Its obvious that 'back in the day', scary "field repairs" were expected, especially upon utility vehicles, just to get through the season, or to sell it off.

                    Can you imagine the additive error of adjustable-reaming both piston and bushings, in several steps, when it comes to staying 'aligned' and 'straight'? So then you were expected to just bend the rod square to the case deck?

                    We can't be that cavalier today. And hope we never have to... ..

                    .....Cotten
                    Last edited by T. Cotten; 07-30-2020, 02:34 PM.
                    AMCA #776
                    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

                    Comment


                    • #11
                      Tom; I bought the piston knurling machine and quite few other interesting tools from an old automotive machine shop that was going out of business 25 years ago. I asked the old guy if it really was a good idea to reuse the pistons? He told me that the knurled pistons retain oil in the skirts and reduce the wear on the pistons and cylinder. He was selling out because his son ( that was to take over the business ) had lost a lot of the co. money to his coke habit.
                      Craig

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                      • #12
                        Its my favorite kind of tool, Craig!

                        Historical, and full of mystery.

                        ....Cotten
                        PS: I tried it Folks,..

                        Pulling the piston skirt against the flat of my chuck with a draw bar.

                        But I always sucked at knurling anyway.
                        Last edited by T. Cotten; 07-30-2020, 05:32 PM.
                        AMCA #776
                        Dumpster Diver's Motto: Seek,... and Ye Shall Find!

                        Comment


                        • #13
                          Tom; The chuck on the machine does not spin 360 deg., but rocks left to right. It has a micro feed ( seen to the right of the forward extended arms ) so you know exactly how much you are bringing out.
                          Craig

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                          • #14
                            Originally posted by 41craig View Post
                            Tom; The chuck on the machine does not spin 360 deg., but rocks left to right. It has a micro feed ( seen to the right of the forward extended arms ) so you know exactly how much you are bringing out.
                            Craig
                            I wish I could fondle it, Craig!

                            360 would be pointless, as only the thrust faces are involved.

                            Some had die-springs to apply the knurling pressure, but extinct no doubt.

                            ...Cotten
                            AMCA #776
                            Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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