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Mercruiser 3.7 litre Knocking "help please"

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  • Mercruiser 3.7 litre Knocking "help please"

    I bought a 1988 Baja Islander 180 in great shape, so I thought. I was told the engine had been rebuilt without proof. The engine & hardware looked almost new. Ran the boat for above 6 weeks when one day going about 25 knots the boat began to loose power and would not accelerate. The engine also began to sound louded than usual. I quickly slowed the boat and lifted the engine cover. It had a knocking sound in the back of the engine. I got it to shore and out of the water. Checked the oil a few days later. It was 2 quarts low. After adding oil and starting it, it sounded fine at an idle. When I increased the RPM's it had a different sound than before, like a clacking sound. I took it to a mechanic who said it was an internal problem. Should I have the engine pulled and is it worth rebuilding if needed? I paid $3000 for the boat and it's in great shape as I said. Thanks, Nick.


  • #2
    Re: Mercruiser 3.7 litre Knocking "help please"

    Could be a couple of things, rocker loose causing ticking sound, which can be a bent push rod or just a loose rocker, usually they do not get loose on their own.

    Rod knock from bearing damage which would require a rebuild or replace.

    How did the oil look? any water in it? Sometimes hydrolocking an engine can cause a bent pushrod.

    I'd pull the valve cover and have a look see and go from there.
    Good luck

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    • #3
      Re: Mercruiser 3.7 litre Knocking "help please"

      The oil looked fine when I checked it. It was dark though. My feeling is it lost oil pressure. I'll pull the valve cover. Do you think this engine is worth rebuilding? I've been told they have alot of problems.
      Thanks.

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      • #4
        Re: Mercruiser 3.7 litre Knocking "help please"

        Tough call, depends on how handy you are and how much you like the boat. There is no bolt in engine that will work except another 3.7 or 470 as there are called. They are one of a kind and no longer made.

        As you can see I have one too.

        If it was mine I would have it rebuilt "if it needed it", but I would be the one pulling the engine, disassembly, and reassembly, everything except for the actual machine work. If you are going to have to pay for it all to be done not sure what it'll cost ya.

        The common issues with the engine are the charging system and water pump seals on the front cover/camshaft, which can be rectified. I've had to do both this year.

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        • #5
          Re: Mercruiser 3.7 litre Knocking "help please"

          Thanks for your help.

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