Shaft seal vibration?

[vandy]

After some help! I changed stern glands and cutlass bearing on a boat new to us with 3YM20 Yanmar engine, I noticed the top end of shaft seal vibrate a lot when in gear and shaft spins but there’s no sign of water dripping etc. Is this normal?

 

[Concerto]

Have you checked the engine alignment?

 

[vyv_cox]

Sometimes the drilling in the output flange on the gearbox is not completely symmetrical. The shaft is therefore slightly non-axial and bounces up and down when running. Ideally you should check this with a dial gauge but a fixed pointer can be nearly as good for an initial evaluation. It is quite common for slight movement of the gland to occur.

This assuming that the movement is not the engine vibrating.

 

[greeny]

After some help! I changed stern glands and cutlass bearing on a boat new to us with 3YM20 Yanmar engine, I noticed the top end of shaft seal vibrate a lot when in gear and shaft spins but there’s no sign of water dripping etc. Is this normal?

How much is "a lot". Maybe you're concerned un-necessarily.
My 3YM20 with Volvo shaft seal vibrates more than I like when at, or around tickover but smoothes out once revs are increased.
It's never leaked or suffered premature wear because of it.
I put it down to the natural harmonic vibrations of that engine.
Is it vibrating all the way up the rev range or just at tickover?

 

[vandy]

How much is "a lot". Maybe you're concerned un-necessarily.
My 3YM20 with Volvo shaft seal vibrates more than I like when at, or around tickover but smoothes out once revs are increased.
It's never leaked or suffered premature wear because of it.
I put it down to the natural harmonic vibrations of that engine.
Is it vibrating all the way up the rev range or just at tickover?

Hi it vibrates mostly at tickover speed and as you said the vibrations almost disappear when I increase the Rev. Can I ask what boat have you got?

 

[Tranona]

Vibration at tickover is common. You don't say what boat you have, nor what the seal arrangement is.

 

[vandy]

Hi, she’s a jeanneau 32i with Volvo seal.

 

[Tranona]

Hi, she’s a jeanneau 32i with Volvo seal.

Ok the only support for the shaft is the cutless in the P bracket and the gearbox coupling so the shaft moves with the engine. The Volvo seal does dampen out some of this movement. So the shaft will move when the engine is running at tickover but should smooth out as revs rise.

However the movement can be greater if the mounts are shot or if the alignment of the engine is out in relation to the shaft when the shaft is central in the tube and the cutless.

 

[greeny]

Hi it vibrates mostly at tickover speed and as you said the vibrations almost disappear when I increase the Rev. Can I ask what boat have you got?

 

[greeny]

Hi it vibrates mostly at tickover speed and as you said the vibrations almost disappear when I increase the Rev. Can I ask what boat have you got?

Hi,sorry it,s taken a while to reply. I'm on the ferry heading back to uk and comms are a bit hit and miss.
My boat is a Ben 323. Yanmar 3ym20 to shaft, then through the Volvo seal into the stern tube inside the log. It exits the log at the cutless bearing and the prop is right there with no overhang and no p bracket.
In my first year of ownership I spent numerous hours aligning the engine and checking engine mounting, but nothing i did would alter the vibration.
After many attempts I gave up and accepted the vibration as being due to the natural harmonic of the engine. That was 8 years ago and it's never caused me a problem. I've changed the cutlass bearing once and the Volvo seal once during that time.