Bravo 1 sterndrive rattling

[Tpitch20]

Hello. So 2019, has not been good. I threw a rod in my 1997 5.7 mercrusier. Bought a brand new 5.7 GM Longblock marine engine and swapped it myself. Runs and sounds great except I notice a loud rattle in the upper unit at like 1500-2000 rpm. Any suggestions?

 

[Thornton69]

Engine alignment or possible air lock in upper case?

 

[Handsome Transom]

My thoughts go to mounts and ot stringer rot and alignment. I would confirm alignment , ,gimbal bearing , and engine coupler

 

[Tpitch20]

Engine alignment or possible air lock in upper case?

I have the alignment tool and it went in perfectly and I was able to turn it with two fingers. I also filled the unit from the bottom with the top screw removed till the oil started to come out.

 

[Tpitch20]

My thoughts go to mounts and ot stringer rot and alignment. I would confirm alignment , ,gimbal bearing , and engine coupler

Pretty sure alignment is good. All the rattle comes from the upper unit. I Removed the top cover to look inside and it looks good no metal filings or chips gears looks solid

 

[scoflaw]

Does the rattle stop with the drive removed ?

There's a lot more to the upper unit than what you can see with the top cover off

 

[Thornton69]

If it started after the swap, it is more than likely an installation issue.
Was any adjustment made to the height of front mounts during your alignment checks? Maybe something isn't right with the rear mounts. Also, when checking alignment, was it confirmed good with the crankshaft in several different positions. You could possibly have a runout issue with the drive coupler and or flywheel.

 

[sbw1]

Assuming you are describing the rattle coming from the I/O "unit", bad u-joints rattle. If that is what it is, a simple cheap fix. Also easy to confirm. Put gear in neutral, set throttle to 1500-2000 RPMs, and turn steering hard to left or right and the rattle gets louder.

 

[Tpitch20]

I have the alignment tool and it went in perfectly and I was able to turn it with two fingers. I also filled the unit from the bottom with the top screw removed till the oil started to come out.

So here’s the update. I’m going with air locked. Today I was preparing to take her out and upon initial start up low gear oil alarm sounds. Reservoir very low. I filled it and no more noise. So I assume the air worked it’s way out and the reserve oil filled the void.

 

[Handsome Transom]

Glad that the easy and least expensive remedy was it. Goes to show you start with the simple things first.

 

[Handsome Transom]

Glad that the easy and least expensive remedy was it. Goes to show you start with the simple things first.

I wonder why it did no trigger an alarm