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Thread: Need Help With an Older Mercury OB

  1. #1
    Member oldakcop's Avatar
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    Default Need Help With an Older Mercury OB

    I have a '75 Mercury 90 Thunderbolt with a dead cylinder. Does anybody know of someone in the Anch./Mat-Su area that does mechanical work on these old Mercs.? The guy out at Big Lake has since retired and he was the only one I trusted with her....

  2. #2

    Talking J Kimberly Services

    They come highly recommended. 349-1894.
    We never really grow up, we only learn
    how to act in public

  3. #3
    Member oldakcop's Avatar
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    Default

    Doug, thanks for the input! However, J. Kimberly doesn't work on the older models. Neither will Marita Sea & Ski and Alaska Mining and Diving. I guess I'll be needing a "Shade Tree Mechanic" who doesn't mind a challenge, if there's one out there somewhere....

  4. #4

    Talking No guts...

    No glory! Tear that bad boy apart. Hopefully it's a straight forward process. Good luck and remember, it didn't run anyway.
    We never really grow up, we only learn
    how to act in public

  5. #5
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    Default let me guess , it's the top cylinder?

    If a "leak down" test is done , (not a compression test) It will reveal the nature of failure. Notoriously the top cylinder runs dry and the piston is toast. or if the head gasket leaks water the steam eats up the piston. check for a clean spark plug that's a good clue.
    The leak down test reveals a lot of things a compression test does not , in fact the compresion test is not reliable sence it depends on the speed of the piston travel, and the compression test is done with an air compressor using a special regultor and bleed system and fixing the piston in position so tht it is not moving during the test, nor do you add oils to (improve compression) you want the truth . Air will leak past the rings and through the gasket leaks , if you hear it through the carb the reeds are leaking too.
    That is the worst senario, at best it is a coil or carb problem , I was trained to test for the worst first . Whom ever you get to do the work it won't be a shade tree mechanic that knows this engine.

  6. #6
    Member oldakcop's Avatar
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    Default Want a Project?

    Arleigh, it sounds like you know this engine! Yep, it's the top cylinder. Want a Project? It seems I'll have more trouble finding someone to do the repair work than I would just buying another engine. It's a shame, I literally just rebuilt the lower unit. The only thing on the jet that isn't new is the bell. I would hate to just give up on the ol' girl. I like the engine, it's smooth and never really gave me much trouble until the last few years. I guess she's seen her better days and needs to be put to pasture. Thanks for the advice!

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