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Shaft alignment

Feb 9, 2005
Catalina 310 City Island, New York City
Just installed new shaft, cutlass bearing, PYI Dripless, coupling, damper plate, transmission, and engine mounts. The vibration is bad, the mechanic who did all the work thinks the allignment is correct, but I know it can't be. The folding prop is installed correctly, I had a diver check it yesterday. I showed him the manual alignment instructions. Did anybody have any helpful tips for aligning the engine to the shaft to solve the vibration. I know this has been discussed, any links would be appreciated,
thank you all,
Dec 28, 2015
Laser, Hunter H30 Cherubini Tacoma
There are a ton of videos on YouTube on the subject. You can watch them for hours on the subject. I'd start there and try to narrow it down to some more applicable to your boat. Was it vibrating the same way prior to the work? Assuming so given the parts replaced.
Feb 21, 2013
Hunter 46 Point Richmond, CA
A powerboat I purchased had one of the new shafts go out of alignment in heavy seas halfway on its 450 mile trip from Los Angeles to San Francisco resulting in significant vibration and cutting engine rpm from it normal 1700 to 800-900 rpm to mitigate it. Once I got the boat home I had the engine mounts adjusted with metal skims to align the shaft/engine, which in my case mitigated the vibration. Lots of other causes of vibration as discussed in these articles: Shaft Alignment | Yachting (yachtingmagazine.com) and How to Diagnose and Fix Inboard Shaft Vibration | Boating Magazine
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Feb 9, 2005
Catalina 310 City Island, New York City
Very little vibration before. The cutlass bearing was was loose and needed replacing, the old bronze shaft was scored and the damper plate was noticably rattling but pretty smooth motoring for the 18 years and 1800 hours I put on it. While everything was off I decided to replace the transmission as a lot of owners reported problems with less hours. The engine mounts looked pretty worn so thought it would help to replace now.
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Likes: MikeHoncho
Sep 29, 2008
Catalina 310 #185 Quantico
Did the diver report your shaft is centered in the opening? Once it is centered then you can focus on the inside alignment. Had a rattle that would not go away until I did that.
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Likes: RoyS


Dec 15, 2006
Catalina Catlina 310 Campbell River BC
when you had all this work done on the hard, did your mechanic do the final alignment of the shaft in the water if not that could be the problem.
Nov 26, 2012
Hunter 34 Berkeley
The procedure for checking the alignment can be found on Youtube. Basically use a feeler gauge to check the gap between the two sides of the flange at top - bottom - left -right. They should all be very close. The new transmission could be the problem. How new is it? What kind is it? I can tell you that the Kanzaki transmission uses a clutch that hammers when it slips creating one heck of a vibration. I went through this a couple years ago. It was a long road to figure it out. That may be the problem.