Do I need a flexible coupling?

alaskaflyfish · Mar 20, 2018

I would recommend one on the basis that it dampens shocks and pulses between the fixed shaft and shock-mounted (movable) engine. Smooths out the rotary vibration as it were, saving your cutlass bearing. Also as a secondary function it isolates the engine form the shaft preventing electrolysis corrosion.

gene_neill · Mar 20, 2018

Thanks Tim! That's the way I'm leaning.Semi-side note: I've been reading about the "2 out of 3 rule". Meaning, between engine mounts, shaft coupling, and shaft seal (three things) only two should be flexible or else you get to much wobble.My Beta has rubber mounts, we're addressing the coupling right now, and as for the shaft seal I'm using a Buck Algonquin stuffing box. Does anyone know if that part qualifies as flexible?

Gazuum · Mar 20, 2018

Not necessary if the alignment is done properly. There are a lot
more boats out there without than with.
Do your final alignment with the boat in the water. Use your
feeler gauges, do it right and you don't need the flex coupling.
That said, if you already have the proper one, it won't hurt
anything if you do use it. But I would still be diligent with the
alignment.
G
On 3/20/2018 7:16 PM,
gene_neill@... [AlbinVega] wrote:

alaskaflyfish · Mar 21, 2018

I have a Buck A. stuffing box. There is a rubber hose connected from the shaft log to the gland nut. It moves around quite a lot with engine pulses. I have a 1gm10 Yanmar and at idle it jumps around like a jack rabbit. The point of rigidity is the shaft cutlass bearing. Everything upstream of that needs to be shock/impulse dampened.

tiempo2010 · Mar 21, 2018

Flexible couplings are not there to allow for shaft mis-alignment. They are there to prevent transmission damage it he prop was to hit something. A very good item to have.

mphalv · Mar 21, 2018

We have a single cylinder 1GM10 Yanmar. It vibrates and moves around a lot more because of being one cylinder especiall at idle. A flexible coupling was necessary, but not need on the 2 cylinder volvo penta that was orginal equipment. It does reduce cutlass bearing wear.
Paul

Double Fantasy

Gazuum · Mar 21, 2018

I tend to disagree.
These transmissions have dics and use ATF for a reason. They are
friction drive. They are made to slip! (But not enough to be
noticeable) Hit something and they slip. Pounding into big seas and
they slip. Slam into gear and they slip. (Maneuvering in the marina)
Hit something underwater such as a tree limb with your prop and I
guarantee your prop is toast. Flex coupling won't save it but you
won't take out the transmission either.
Flex couplings were invented to reduce alignment issues. Most back
yard mechanics (and many marine mechanics) don't have a clue how to
align the shaft so they install a flex coupling. Not really a bad
thing. Just saying.
Think about a flex coupling. Is it made to flex rotationally? No.
It is made to flex side to side. If you have alignment problems, the
flex coupling will save wear and tear on cutlass and transmission
bearings. So again it isn't a bad thing.
g

On 3/21/2018 7:45 AM, Brian Stannard
brianstannard@... [AlbinVega] wrote:

alaskaflyfish · Mar 21, 2018

I guess it depends on your transmission. Mine definitely does not use ATF. Shaft alignment is not a constant. Engine shock mounts settle and flatten over time, engine beds compress and the hull flexes as well. You don't need a flex coupling but it sure helps and is a good idea. My 1gm10 yanmar has power-pulses every 720 degrees of crankshaft rotation and without the benefit of a gyro stabilization dpmpend flywheel, so the flex coupling in my case helps absorb (some) of the rotational shock.

mphalv · Mar 21, 2018

Tim,
Same with my 1gm10. At idle it is doing the hula shimmy

Paul

Double Fantasy

gene_neill · Mar 21, 2018

I was just looking at the Vega Association of Great Britain's page, where they sell (or used to sell?) Beta packages. I notice they advertised that all their Betas came with a flexible coupling. Interesting ...