Run Out Shaft Vibration

[dvd]

I have a late model A-4 with 2 to 1 reduction and a new from Martec Folder. I have always had some vibration at low to to mid range cruising speed. I recently had the 1 inch stainless shaft replaced, put on a Federal Flexible coupling and replaced the cutless bearing. It didn't seem to make a dramatic change in my vibration. My understanding of run out vibration is that it occurs and causes vibration because the shaft is not spinning true but is turning in a somewhat elliptical fashion. I have also read that if there is a run out issue that it will be less noticeable at the higher cruising speeds which tends to fit my symptoms. Anybody ever dealt with this or have any explanation for this. DVD

[ArtJ]

Have you checked the engine to shaft alignment by inserting a feeler gauge
between halfs on all 4 sides of the coupling?
The engine bed is shimmed to make each 1/4 revolution measure the same.
Regards

[High Hopes]

My boat had a bad vibration which proved to be the cutless bearing.

[dvd]

I haven't actually re aligned the engine since I had the new shaft installed but it was aligned prior to this installation and was ok. Since I am still experiencing same vibration I haven't bothered with it yet. The new shaft was installed about 1 month ago. At the advice of Don Moyer I spoke with someone at Indigo about the run out issue and he indicated what I discussed at the beginning of the thread. There is a guage that can be used to check run out call a Dial guage or something like that. Instead of the shaft turning true its hopping around eliptically causing vibration. The only way that I can picture this occurring is when you have defective prop side coupling that has somehow become elongated or is off center?? DVD

[Mark Millbauer]

DVD,
In order to diagnose a problem, the technician must rule out possibilities starting with the very basics. ARTJ is right on. May I suggest that you check the alignment, and then get a dial indicator and then check the shaft. A mis-alignment of the engine and shaft could also show with the dial indicator so just using a dial indicator won't really tell you the problem until you can rule out engine alignment. If you check and adjust the alignment and it still vibrates, at least you know it isn't that.
Are you still using the same prop? In looking at your previous posts, it appears that you are. it could be a constant here and if so, it (the prop) could also be causing the vibration. I woudl start with engine alignment first.

Mark

[David Masury]

Instead of using a feeler gauge at four points around the coupler, use thin shim stock. You can get thin shim stock at most hardware stores, they have a little display with hobby type metal.

When redid my cutless bearing, I re-aligned the engine. I cut the thin stock into strips about two inches long and about 3/8 of an inch wide and placed the four pieces between the coupling halves. Then I slowly rotated the coupling by hand. The ones that feel out of the coupling obviously indicated a larger gap at that location. I adjusted the engine and re-did the four pieces, until they all stayed in place and felt about the same amount of tension.

David

[ndutton]

All of the foregoing assumes a straight shaft. Even a slightly bent shaft will make quick work of a cutlass bearing and rattle your fillings. With a worn cutlass it's easy to assume that's the problem when maybe there's something wearing it out. The only 2 things I can think of are alignment or a tweaked shaft - or both.