7.4L Vibration

[StuartT]

The 2859 I am working on buying in California demonstrated some vibration during sea trials on Friday. When we pulled the boat out of the water, I noted some very rough edges around the prop but no bends I could see in the blades. There was also some broken off mussel remains on the blades which might have caused some cavitation.

The owner has agreed to send the prop out for repair, but if it comes back and there is still vibration, I am going to insist the B2 leg be pulled. My question is, what are the causes of outdrive vibration in the order of most likely to least likely. Gimble bearing, motor mounts, simple alignment, other, other, in what order? FYI, the 7.4L seems to be very smooth at all rpms in neutral.

[wickus]

The vibration level before I switched from Al to SS was staggering. I'll never have a Al prop again. It literally rattled the engine compartment to obnoxious noise levels. I'm guessing the prop. Good luck.

[SomeSailor]

Yep. Stainless is a real treat after driving around for even a short time on aluminum. Pull the prop and check the prop shaft. He may have bent it. If the vibration is still there, it could be a bent input shaft, u-joints, coupler, engine alignment, gimbal bearing. Are you getting noise? Does it change as you turn the steering?

What happened to the one you had in Gig Harbor? Did you drive all the way up and it didn't work out?

[StuartT]

I didn't think a balanced, properly formed aluminum prop could cause vibration, so that's an education for me. No, there was no unusual noise, just the vibration in my feet standing in the middle of the cockpit. Turning did not seem to make any difference so I am thinking alignment, possibly bad motormounts, or drive components like you point out.

I was going to post the Gig Harbor story so I'll do that this morning.

[SomeSailor]

There is I believe a certain amount of natural resonance in a 2859 that you'll feel in your feet. Stick the prop in deep and it becomes more pronounced. I personally believe it's mostly because of where the hull resonates and where your feet are in relation to where the hull is on surface of the water.

It's not nearly as pronounced with the prop trimmed out a bit and the stainless prop really helps. It's also a huge difference in the quieter shifting as well.