Stern tube, flexible shaft coupling, cutlass bearing

[TJBurkett]

Hi all,

Having had some trouble with the prop shaft coupling on Pagan Baby this winter I disassembled the dripless shaft seal, removed the coupling, and pulled the shaft. In doing so I noticed a couple of logitudinal cracks in the bronze stern tube that had been covered up by the bellows from the shaft seal.

So now I'm contemplating wraping a couple of layers of glass and epoxy around the broze stern tube to seal/bind the cracks and then replacing the bellows for the dripless system-hoping that will be enough to stop the cracks or limit their expansion. I'm also considering installing a flexible linker between the transmission flange and shaft coupling to reduce vibration, and while I'm at it, replacing the cutlass bearing.

What do people think of flexible shaft couplings-pros and cons, and has anyone replaced the cutlass bearing on their Vega? Has anyone seen similar cracks in their stern tube?

Thanks,

Tom

Pagan Baby V-398

 

[tiempo2010]

I am not a fan of dripless couplings, but if the stern tube is cracked I
would replace it, not use a band-aid fix.

 

[SVFlyAway]

When I put my Beta in, I put in the Volvo shaft seal (Hallberg-Rassy used
it on my 39 when I had her, so if it is good enough for HR is it good
enough for a Vega). My bronze tube had a big chunk broken away at the
forward edge, but I was able to cut that part off and still have plenty for
the seal. I probably wouldn't glass it. Maybe a really good welder could
repair the tube without burning the glass? Perhaps? If you are set on
applying glass, consider Kevlar instead. It is expensive, but in this small
amount it would be trivial. I often wondered how one would replace the
stern tube, never tried to do one. Easy to put it in, but not sure how to
get the old one out!!!

I use a Centaflex flexible coupling. I raced on a boat years ago and after
the return trip from Honolulu to Seattle the first stop was in Port
Orchard. A couple days later the crew was rested and went to take the boat
down to Seattle. The engine ran fine. The shaft would turn at idle speed,
but put on any power and the thing didn't move. The boat's owner flew up
with his mechanic and they discovered that the coupling was broken. Not a
surprise I guess. it was nothing more than a piece of heavy, thick rubber,
bonded between two metal plates one attached to the transmission and the
other to the shaft. One of the plates had come unglued from one of the
metal plates. With no resistance on the prop at idle speed there was enough
friction for it to turn the shaft. But any power and the prop wouldn't turn.

By the way, if you put on a Centaflex or probably coupling you have to
really reef it down. I put mine on "snug" and the shaft backed out.
Fortunately I didn't lose it entirely. I now have a zinc on the shaft on
the inside incase the shaft were ever to come loose. Strange I know, but
again not expensive and far better than a hose clamp.Steve Birch sells the coupling and the shaft seal (at least that is where I
got mine).

 

[pjacobs55]

I picked up a Volvo shaft seal for the Ballad. I notice at the bottom of the instructions it says
"Note! The rubber stuffing box is not recommended for installations where flexible couplings are being used."

I don't know why. Anyone have any ideas?

My stern tube on the Vega was worn thin on the forward end from the shaft knocking on it. I cut it back 1/2" (12mm) to find some thicker tube to clamp the stuffing box to.

I think it was caused by 2 worn out rear engine mounts, a worn cutlass bearing, and poor alignment. It seems good with these problems fixed. Tom, if your tube is cracked there might be a similar reason.

I think I'll convert to the Volve shaft seal in the Vega, as they look really simple and have an excellent reputation ... and they're relatively cheap!

Chris, I like your idea of adding an "insurance" zinc ahead of the stern tube to prevent shaft and prop loss ... I'm putting that on my "To Do" list.

Peter
#1331 'Sin Tacha'