Mercruiser 165 Exhaust Chirp

[sreiner]

I got a new boat last fall with a Mercruiser 165 straight six (1970 Thunderbird Comanche). The boat has been garaged since new and is in excellent condition for being 50 years old. I serviced the drive over the winter and installed a new long block since I discovered the original block had been cracked and JB welded by the PO. I also rebuilt the carb, replaced all ignition components and upgraded to electronic ignition. The engine runs great and smooth. The only issue I'm having is a chirping noise coming from the exhaust. You can only hear it when it is running on muffs as it is only coming out of the propeller. In other words there is no noise in the engine compartment. I thought it might be the gimbal bearing, but I figured you would hear the chirp from the inside of the transom if that was the case. Also, the bearing felt very good when I inspected it. Has anyone else experienced an issue like this? Thanks in advance for you input!

 

[kenny nunez]

Do a compression test to be sure the noise is not a leaking exhaust valve. The only other thing could be an exhaust flapper that has broken loose and is lodged in the exhaust stream.
When the engine is running does the noise change when the drive is moved left and right? A very slight rattle is normal according to Mercruiser.

 

[alldodge]

Might be in the drive, run it without the drive on

 

[sreiner]

Thanks for the replies. I will try these suggestions as soon as I get a chance.