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1991 Johnson 115 HP Engine Knock

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  • 1991 Johnson 115 HP Engine Knock

    After running across the lake, I slowed to cross a large wake. When I slowed, I noticed a knocking noise coming from the engine. I turned the engine off and removed the cover to inspect. Everything looked fine. I cranked the engine and it still knocked. I figured it was a goner, so I ran at 3000 RPM back to the marina. As I idled through the marina the noise faded. Finally at the dock, the knock had disappeared. In neutral, i ran it at 3000 rpm for about 30 seconds but no knocking. Back at home, I hooked up the garden hose and ran engine tuner through the engine thinking i might have carbon build up. After sitting for several hours, I ran it several minutes at different RPM's and still no knocking. It clearly was not a lower unit noise. Any ideas what it could be?


  • #2
    Re: 1991 Johnson 115 HP Engine Knock

    Sometimes, two strokes that aren't getting enough oil will knock under load. Also extreme heat can cause one to knock. Hopefully it is something simple.

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    • #3
      Re: 1991 Johnson 115 HP Engine Knock

      Could this be an indication my VRO is not operating correctly?

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      • #4
        Re: 1991 Johnson 115 HP Engine Knock

        I must appolgise I do not know a lot about boats, but if a VRO is an oil injection system I would suspect it could cause the problem. I have worked on a lot of two strokes race bikes. Most two strokes that are not getting enough oil will knock first, then if loaded hard enough or lack enough oil will seize. The seize may only last until the engine cools, but you can be sure it is damaging. I am not sure this is what is happening. It is only one possibility

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        • #5
          Re: 1991 Johnson 115 HP Engine Knock

          IF this is a crossflow engine, I would check for loose upper crankshaft bearing housing bolts, and drain gear oil and check for chunks of metal.
          Help somebody every day, if you can.

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          • #6
            Re: 1991 Johnson 115 HP Engine Knock

            The gear oil was clean and in good shape. No metal shavings were found in the oil or on the screw magnet.

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