Rattling/Knocking noise on Mercruiser 3.0 L... Help!!

[SamShapiro]

Hello! I have owned a 19 ft runabout for the past year and in the past few weeks there has been a knocking/rattling noise that has gotten worse and worse. It is noticible at idle, and is deafening at any RPMs above idle (see attached videos for idle & about 2500 RPMs).

The boat was recently in the shop as the starter motor had been acting up (ended up that it needed to be tighted as it had loosened itself), and the belts have been recently changed, non of the pulleys on the alternatator or the water pump make any noise themselves. I also pulled out the mechanical fuel pump as knocking/clicking seems to be coming from that general area, I have the picture of the fuel pumps mechanical trigger attached - not sure if the wear looks normal.

I am a bit perplexed as to how to being diagnosing and would love some advice!

Thanks in advance!!

 

[Rick Stephens]

Use a stick or a mechanics stethoscope to isolate where the noise is coming from.

Pull the drive, stuff a cutoff hose in the water port on the bellhousing and see if the noise goes away.

 

[SamShapiro]

Use a stick or a mechanics stethoscope to isolate where the noise is coming from.

Pull the drive, stuff a cutoff hose in the water port on the bellhousing and see if the noise goes away.

Thanks Rick - cant pull the drive as the boat is in the water, and i dont have anywhere on land to work on it... Is this to isolate if the noise is coming from the engine or in the drive?

 

[Rick Stephens]

Thanks Rick - cant pull the drive as the boat is in the water, and i dont have anywhere on land to work on it... Is this to isolate if the noise is coming from the engine or in the drive?

If you have a knock you can't use it till you fix it. If you cannot locate it with a stick held against your ear, or a stethoscope, then pulling the drive to remove that moving part is next in line.

 

[SamShapiro]

If you have a knock you can't use it till you fix it. If you cannot locate it with a stick held against your ear, or a stethoscope, then pulling the drive to remove that moving part is next in line.

Got a stethoscope and it seems to be coming from the rear of the engine, where the bell housing meets the drive. It’s a metallic sort of noise - bad gimbal or something? Doesn’t sound like it’s coming from the engine itself though…

 

[Rick Stephens]

Gonna have to pull the boat out, pull the drive and start looking.