1972 Mercruiser 140hp 3.0L Noise from elongated transom plate mounting holes?

[AndyFromWI]

For the past 10 years I have been trying to solve a problem on a 1972 glastron with a terrible knocking sound.
At first we thought it was the engine, so we pulled it for a rebuild, but the engine was fine.
The engine sounds great on a engine stand.
I have swapped lower units, no change.

Years ago someone suggested replacing the motor mounts. Two days ago I pulled the engine installed new motor mount bushing on the rear of the engine and in the front motor mount assembly (have not yet re-installed the engine).

Looking at the rear transom plate, there is significant play in the holes that the rear engine mounting bolts go through. I'm wondering if anyone has had experience with this and if this might be the cause of the noise.

Here is a video of the engine running after the last time I pulled it: https://youtu.be/H3FkW2j77Nc

Video of the play in the transom mount: https://youtu.be/v7Rv1_EiRuI

I do plan on also replacing the rear bolts and getting new parts for the front engine mount.

My main concern is the play in the rear transom mount.
Here are two pictures, it is hard to see but there is play/wobble when you put the bolts in the holes.


Any suggestions would be appreciated, thank you.
-andy

 

[kenny nunez]

I would not worry about the larger hole. The main thing is you are replacing the motor mount bushings and after the engine is back in and you set/check the alignment go fishing !