shaft vibration

[robert]

my 29.5 shaft vibrates when the rpms are above 1200. Below this its fine, when the engine was disconnected from the shaft it ran to 2900 rpm with no vibration. what is the next step the boat is in the water , any ideas?

 

[Harry]

Might be

Go over the side and inspect the shaft for: Marine growth, barnacles, a half corroded shaft zinc(s), fishing line wrapped around the shaft. Then check the prop for the same. If all is clean see if you can move the shaft in cutlass bearing, a very small amount of play is normal. If all of the above seem OK then the shaft may be bent or the prop may have a blade bent or nicked. The prop can be removed under water if the nut is not frozen on, but if the shaft is bent then a haul-out, shaft removed, and taken to a machine shop is the only way to get it set right.

 

[Bill Murray]

alignment?

could just need to have the engine aligned with the shaft. Instructions are in your owner's manual or pay your mechanic to do it and watch.Bill Murray Good Faith H29.5

 

[Mike]

all of the above

Yes I agree with the others, it is either something bent, something on the shaft that doesn't belong, a worn cutlass bearing, and out-of-balance prop, or a misaligned shaft or some combination of these things. A little play in the bearing is a very nebulous thing....everybody has a different idea of what a little play is. I would consult with a pro on that one.Regardless, don't let this condition go for too long because like all things mechanical, if you ignore it you WILL eventually pay dearly.....