serious prop shaft vibration

[Chief Engineer]

I was refering specifically to the yanmar engine in this case and the yanmar mounts.

And as far as a prybar goes...you are looking for motion not by jumping up and down on it, but rather even pressure with your arm.

It is rather alarmist to say you are shearing off accesories or bending the oil pan.

You place the bar near the engine mount next to the stud. You never use a prybar on sheet metal

[RBEmerson]

Well, let's put it this way, there is a potential for doing damage to an engine with a pry bar improperly applied (not everyone has the good sense to know where and how to apply it). Shoving the engine around doesn't offer the same potential. And past that, as I said before, I humbly beg to differ, but I do stand by my comments.

[ozskip]

Well if you have a folding or feathering prop my guess is growth in the mechanisam and making it not change the pitch properly at slow speeds.Greg

[never monday]

is the vibration random or cyclic?
what trans was fitted to your engine?

[Chief Engineer]

I looked up the Manecraft seal....It appears that it needs cooling water. While I have no experience with Manecraft, if it is similar to a Tides seal that require cooling water
I know that Tides Seals will self destruct if they do not get the cooling water. I have seen Tides seals literally fuse to the shaft. Could it be that the portion on the stern tube has worn severely?

[RBEmerson]

+1 on that! There are a number of seals that either need water flow or at least contact with water to avoid cooking the seal. The reported symptoms are consistent with a cooked seal and (probably) a scored prop shaft.

[Chief Engineer]

I hope he gets back with us to tell us what happened.

[Maine Sail]

Make sure you don't have a broken mount or bell housing foot.. this was caused by floating poly line that stopped the engine from full cruise RPM..

[drinky]

Thanks thanks thanks and many more. It is really great to post a problem and in no time have a huge range of probabilities and cures sent as answers. (1) The mounts are good. (2) cutlass is ok (3) shaft is in line (4) idle speed is maybe only a few rpm slow. Fix that in the morning. (5) The main problem was a large growth on one side of one blade of the prop. Cleaned that up and all smooth except on idle but that improved as she warmed up.
The seal part of the manecraft thingo is still not concentric to the part attached to the shaft tube but it appears to be ok. Plenty of water from the feed pipe and the shaft tube is full anyway.
Will watch the excentric thing. Once again thanks to everyone. This forum is the best thing I have ever found, apart from my boat.

[Chief Engineer]

Yeah as my momma said "You boys put your heads together......and ya got a half a brain".

This board is pretty good as long as there is no pontificating Yes, Virginia I may have been guilty

[RBEmerson]

Dinky, item 5 is a very good explanation for the problem, too. Clean the prop (which, I take it, has happened) and after that keep an eye on things. An out of balance prop at speed is going to whip things around, of course. However, I keep hearing things that would have me thinking about pulling the shaft and generally looking things over for excess wear (or close to it).

[Kym]

hi Drinky , recently had problems with my lift pump which caused excessive engine movement at cold idle. Pump started leaking from corrosion from drip of water from above it (Yanma20hp) Fitted new pump engine idles like a dream. have now reduced revs to standard. So low pressure side of fuel system must have been down too low!!!

cheers