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Old 09-01-2019, 08:09 AM   #1
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Default Mercruiser 3.0 knock

Hi people, I bought 1800sr last year and the guy I bought it from said it had a knocking sound because of old valves. It was a good price so I bought it without checking everything. Put it in the water late last year so I didn't replace the valves and drove it as is. It had the knock but drove okay. This year I had the valves replaced and a big maintenance but still, its knocking.

It knocks louder when it's cold and in neutral and low rpm. I don't know if it knocks when I'm cruising or I just can't hear it. I will post a youtube link to a video I filmed so you can hear it and maybe give me some advice, thanks in advance.

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Old 09-01-2019, 11:46 AM   #2
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Video doesn’t work.

Bad valves cause a ticking noise not a knocking. Knocking if continuous is main bearings and if periodic is a rod bearing. How is the oil pressure? When the mains go so does oil pressure.

Try removing one spark plug wire at a time, if the knocking changes that’s the cylinder with a bad rod bearing.
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Old 09-01-2019, 11:47 AM   #3
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Is it working now?
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Old 09-01-2019, 01:51 PM   #4
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Quote:
Originally Posted by MilosJ View Post
Is it working now?
Yes, try removing one plug wire at a time to see if a change happens.
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Old 09-04-2019, 01:35 PM   #5
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The video works for me. That is not a valve ticking. That is a bearing. It's not a constant rhythmic knocking. There's no pattern to it.

Cautionary Tale: A seller will always tell it "It is only <this>. For a few bucks that can get fixed right up".
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Old 09-04-2019, 01:43 PM   #6
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“Cautionary Tale: A seller will always tell it "It is only <this>. For a few bucks that can get fixed right up".[/QUOTE]”

To funny, most common line I’ve heard given to folks is it just needs the carb rebuilt. Then the new owner finds out the engine is toast.
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