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Thread: Oversized Wrist Pins

  1. #1
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    Default 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. #2
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    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 at 07:24 PM.
    Eric Smith
    AMCA #886

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    Quote 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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    Quote 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

  5. #5
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    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

  6. #6
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    Quote 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

  7. #7
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    Quote 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!

  8. #8

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    It's to avoid replacing the pin bushing.

  9. #9
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    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

  10. #10
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    Quote 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.CIMG1821.jpg

    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 at 02:34 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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