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Thread: M725 with a civi 230- bad rod bearing advice?

  1. #1

    Default M725 with a civi 230- bad rod bearing advice?

    Helping a friend out at a museum. The 725 had a bad rod knock and #5 bearing is trashed with material transfer to the con rod ends. The crank rod journal is ok, but needs to be polished. We are not going to take it apart further and I am trying to figure out the best course of action. I think it is going to be just get a new bearing and reassemble. The rod journal is at 2.055" (measured with a cheaper digital caliper).

    What would you guys do? What size bearing would you recommend?

    Thank you
    Mark

  2. #2

    Default

    What would you guys do?
    Most of us would probably swap in a SBC or maybe even a BBC.

    But being as you are a museum, I guess the question is how much do you run/drive the M725. You might be able to find a running motor or a donor motor. Repairing your current motor without doing proper machining might not last long. Or it might last longer than you or I will be around.

    You could get a stock bearing and use plastigage to make sure the tolerances are ok before reassembling.

  3. #3
    Join Date
    Dec 2003
    Location
    Giddings, Texas
    Posts
    7,729

    Default

    Just dropping the pan and doing the new bearing/plastigage thing as suggested above is your best bet.

    If you have to pull the engine, then you might as well get another engine. That is the best option cost and time wise. Most people give running 230 engines away for little or nothing. I got 4 that way. Plus a civilian engine too.

    A person here in my small town had a rod knock on a stock engine. He went the machine shop route and spent almost $5K on getting everything perfect. The truck has sat in a field for the past 15 years. He won't sell for less than the bill he spent on the engine, so it sits and rots.
    Remember if you didn't build it you can't call it yours.

    6.2 powered M715, 5 M1009's, M416, 2 M101's, 2 M105's, 3 M35's, M1007 6.5 turbo Suburban project called Cowdog.

    https://www.youtube.com/channel/UCCz...HGkBCfhXZ5iuaw

  4. #4
    Join Date
    Jan 2011
    Location
    Fernandina Beach, FL
    Posts
    3,689

    Default

    Quote Originally Posted by Barrman View Post
    Just dropping the pan...

    A person here in my small town had a rod knock on a stock engine. He went the machine shop route and spent almost $5K on getting everything perfect. The truck has sat in a field for the past 15 years. He won't sell for less than the bill he spent on the engine, so it sits and rots.
    Penny Wise and Pound Foolish. I have seen that all too many times...

  5. #5

    Default

    Too bad its the #5 rod bearing. Gonna be hard to find. 2-4-6 are plentiful and I have many in std, .10 and .20 but never could find 1-3-5.
    SFC, HQ,129th Sig Co, PAARNG, Vietnam Era

  6. #6

    Default

    Thank you- I know that ideally a power plant swap would be the best (that's what I did to my M715 years ago) but that is not in the budget...

    Is 2.062 the correct con rod journal diameter? If so I am .007 UNDER already with my 2.055. This is ugly.

    Anyone in MN with a 230 lying around?

    Thanks
    Mark

  7. #7

    Default

    If local I have a short block you could have free. Too far to ship.
    SFC, HQ,129th Sig Co, PAARNG, Vietnam Era

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