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I have noticed in recent months an increase in vibration with the motor in gear.

The motor is a Volvo MD17C, driving an 18", two blade prop' via a mechanical gearbox.

The engine mounts look OK. They have been there for some time, close to 25 years, but they look fine and I have checked the alignment with the feeler-guage technigue. The variation was less than 2 thou over the diameter of the coupling.... see picture below.
The mounts are still on the market.... see picture below.
They were chosen known to be rather stiff, and vibration was present of course. We would choose a rev that was most settled.
Last year, when out of the water, the cutlass bearing also looked fine. There was no excess play in it.

When out of gear and revving normally, the motor is as smooth as it has ever been. The gearbox is fine also.

Rather puzzling.

Thanks.
 

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Prop condition? Growth on hull or prop, corrosion, bent, loose, something around the shaft, bent shaft
 

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Other posters are most likely correct but what is your experience level in judging the "look" of motor mounts ?
Do you have closeups of those mounts ?

Last year my motor mounts looked good but I had a significant vibration. What I could not see til' I removed them was that the port forward cast frame that secured the mount was fractured at the block.
 

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I am also chasing down a vibration and potental rpm issue. I looked at my motor mounts and they also look good but they 25 yrs plus old. Boatyard stated they typically look good but when you remove them, that is when you will the issue and they recommneded having them replaced, if anything, they are 25 to 30 yrs old.
so I have added another project to my list for this winter...
 
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