Stern Tube

[John C]

I have a problem with shaft vibration in my 34, at certain rpm (it varies) the shaft vibrates and knocks violently. The engine rocks around on the mounts and even stalls at low rpm in gear. I believe this is caused by a worn bearing in the stern tube. The cutlass bearing has no play but their is easy a quarter inch play in the shaft were it emerges from the boat. I have checked this by diving. The engine has been aligned to try and fix this to no avail. The shaft is stainless and less than a year old. Anyone had a similar problem and had to remove the stern tube and replace the bearing?

 

[Ron Dague]

Stern Tube Bearing?

I might look foolish when others post, but I don't think that there is any bearing in the stern tube. I'm assuming that you are talking about the tube through which the propellor shaft exits the boat. There is packing material, impregnated with a grease or teflon, that is compressed by a pair of nuts on the inside of the tube. You loosen it so just a little water drips, prior to using the engine. But no bearing in there. Even if you have one of the dripless seals, it really isn't a bearing, more of a seal with mated surfaces, teflon, graphite and some other hi-tech stuff.But as to your problem, 1/4 inch of play in the propellor shaft after exiting the hull seems like way too much! If mine has any lateral movement, (also on a h34), it isn't noticable. I was just under 2 days ago, scraping barnacles off the shaft! In fact, wth 1/4 inch of play, I would imagine water would stream in at such rate that your boat would be on the bottom, pretty fast!I would look at the coupling of that shaft to the engine at the flange. The bolts that fasten that flange together can easily come loose, especially if they've been replaced with new stainless steel. I used those stainless steel nuts that are self-locking (with the plastic one-time inserts) after mine came loose a year ago. Or you can use iron, like mine originally were, and the rust will eventually seal them!

 

[R.W.Landau]

Just a few things to check

John,Working from outside in, If the prop is damaged, it will cause vibration. If the cutless is worn, there will be play in the shaft ,this too will causer vibration.From the cutless(If the strut is not loose), the next solid connection is the shaft to transmission connection.The stern tube is only a port to accept the shaft. The packing glad inside is only to keep water out.My guess is that the shaft is bent or the alignment was not done properly.If there is any play between the shaft and the plate , you my have a connection that is not square to the shaft.What I don't understand is play near the stern tube.If the cutless is good and the shaft is bolted on, there can be no play except for shaft deflection.Start the engine, put it in gear and look at the prop shaft where the packing gland is.If you see a wobble, check the alignment. If it is not the alignment, Pull the shaft and have it checked. If you have wrapped a rope around the prop, chances are the shaft is bent.If the prop were bent , the vibration would probably continue through all speed.If you can respond to anything above it may help to narrow the problem.r.w.landau

 

[SteveC]

Have you checked your motor mounts.....

you mentioned that the engine rocks around and that might be due to worn engine mount(s). I had one that that was definitely bad, which allowed the engine to vibrate more than it should, which in turn caused the shaft to knock against the side of the stern tube. Just because the mount(s) look ok does not necessarily mean they are ok. I believe there is a procedure to check them that is outlined pretty good in the SELOC manual for Yanmar. When i investigated my problem, I could actually see the engine vibrate severely at certain speeds on the one bad mount. All other components in my drive train were ok.

 

[jim oursler]

diesel vibration

The Drive Saver really works.. It is a slightly elastic coupling that eliminates hard coupling between transmission and drive shaft. It is advertised in many sailing magazines. Installed on my Hunter 34 with Yanmar 3GMF20 drive train and eliminated vibration noise. It was a very tight fit.. had to trim much of the stern tube rubber hose.. but have had now for a year with no problem. Can't remember price.. around 200 bucks. You can do this while the boat is in the water.. with only minor flooding. The Yanmar service manual says that the diesel will resonate at some speed with the hull, and to simply change speed slightly. You mentioned your engine stalling.. and I know this won't cure a stalling problem. Maybe you have two problems.. vibration plus a diesel problem.