Mercruiser 7.4 clattering/knocking sound video

Walt T

Walt T

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Re: Mercruiser 7.4 clattering/knocking sound video

Coupler or exhaust flapper. Classic. Possibly U joints but doesn't sound like those to me.
 
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J

Johnny1912

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Re: Mercruiser 7.4 clattering/knocking sound video

Walt T said:
Coupler or exhaust flapper. Classic. Possibly U joints but doesn't sound like those to me.
Click to expand...



Hi,

Thanks for the reply.

Is there anyway i can test if it is the flappers or coupler while boat is in the water?

Would flappers make such a loud knocking sound?

It's very difficult to work out where the sound is coming from but does seem like it's near the transom end.

Many thanks,

Jon
 
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Bondo

Bondo

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Re: Mercruiser 7.4 clattering/knocking sound video

Ayuh,.... Do a compression test, 'n you'll know Where to look,...
 
Volphin

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Re: Mercruiser 7.4 clattering/knocking sound video

That's no exhaust flapper, too deep. I'd have those valve covers off in a second checking the valvetrain and a compression test asap. Sounds to me like a bent push rod or con rod. Have any trouble starting it lately?
 
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Fun Times

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Johnny1912

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Re: Mercruiser 7.4 clattering/knocking sound video

Just performed compression test, here are the results:

Cyl 1 = 142
Cyl 2 = 146
Cyl 3 = 140
Cyl 4 = 147
Cyl 5 = 139
Cyl 6 = 145
Cyl 7 = 144
Cyl 8 = 139


I did notice one or two of the plugs were quite loose, gonna put them back in now.

Any more suggestions? Motor starts easy, good response from throttle, no smoke at all..


Jon
 
J

Johnny1912

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Re: Mercruiser 7.4 clattering/knocking sound video

Volphin said:
That's no exhaust flapper, too deep. I'd have those valve covers off in a second checking the valvetrain and a compression test asap. Sounds to me like a bent push rod or con rod. Have any trouble starting it lately?
Click to expand...

Hi, thanks for the help..

Please tell me what i should be looking for under the valve covers, exactly what you would do..

I did compression test, does that tell us anything? results below

Cyl 1 = 142
Cyl 2 = 146
Cyl 3 = 140
Cyl 4 = 147
Cyl 5 = 139
Cyl 6 = 145
Cyl 7 = 144
Cyl 8 = 139

Jon
 
tpenfield

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Re: Mercruiser 7.4 clattering/knocking sound video

Good video, (we don't always get that). Compression numbers look pretty good.

With valve covers off, you would be looking for signs of a bent pushrod, dislodged rocker arm, or loose rocker arm, etc. Just a vale mechanism that looks out of sorts.

Are you able to isolate the noise to a specific area on the engine?
 
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J

Johnny1912

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Re: Mercruiser 7.4 clattering/knocking sound video

Sorry, been so long...
Pulled motor, problem was worn teeth on engine coupler!!


Thanks all
 
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