Right off the top of my head, how about engine mounts? Everything tight? Sounds like a prop issue, but if you had it balanced..Hmm. Curious to see where this goes..
Sean

I have seen several boats with unexplained vibration that were fixed by aligning the engine to the shaft, as Docsnow says. You have to get the engine centered on the shaft, and have to mike around the flanges to make sure that the engine is not just in the right position, but aligned correctly.

Just as a point of information, I have to undo the linkage on the rudder to get a prop off, but do not have to pull the rudder. It should be the same for a shaft.

Seems odd it would vibrate before and after truing up the props.. If the coupling was that far out of alignment wouldn't the strut bearing be worn out in some unusual way?
Sean

JC
What year Marinette due you have?
The 1" rubber spacer is a GLOBE Drive Saver. These are a very expensive replacement for the original fiber spacer between the couplings. They are part of the isolation system, by the way the original spacers are no longer available.
The way to check your trans coupling to your shaft coupling is to remove the rubber drive saver and pull the two couplings together. The boss on one coupling fits into the other. From your post it sounds like your strut is out of alignment. On mine the strut was bent, I repaired it and when it was re installed the shaft would not go threw the stuffing box tube. I made up a spacer tube with outside diameter of the stuffing box tube and the inside diameter of the shaft.[note] I cut it in half after makeing for easy removal when alignment was finished. Remove the stuffing box after you remove the shaft from the boat. Install the spacer tube. The strut needs to be removed as well. Now put the shaft threw the spacer tube and temp install the coupling to the shaft. Pull the shaft coupling up to the trans-engine coupling. If the boss of one coupling fits into the other than this is good. {note} The stuffing box tube is fixed, cant be moved, but the trans-engine and the strut are adjustable.
If the boat was running good before the strut was bent chances are the trans-engine to the shaft alignment are close.
If so you can now install the strut on to the shaft, you should notice that the strut should pass by the out side of the rudder. You can now determine what shim you will need if any to attach strut to bottom of boat. after you have done this check to make sure the shaft turns by hand while the coupling is bolted up to the trans.[use two bolts to temp hold couplings together] If everything turns freely, remove temporary gage that was installed in stuffing box tube and remove coupling and reinstall packing box, its a good time for new packing. Re install coupling to shaft and re install prop. After launch in spring you will need to fine tune the trans-engine coupling to the shaft coupling. The boat should be in the water in order to check alignment. Than you can re install the globe drive saver.
Bill


for you

My 28 Express is a 1979 with the 1" shaft. It has always had more vibration than I think it should. When I had the strut off it was inspected by a boat machanic and a man who runs a machine shop (also made the shims) and they did not think it was bent. The strut looks like an airplane wing and I think a bend could be seen. I talked to John at Marinette and he said there was only one strut made for a 28 single 1" shaft.

Tomorrow I plan to try again at alignment of the engine. I have talked a friend into helping with this prlject and he promiced he could hold me upside down over the bilge until I can complete the work.

I appreicate all the help and advice, I will let you know what happens.

John

Jeff is correct as always.

This may seem obvious but it is a 3D environment.

I usually work on left/right alignment first then up and down but it truely is an upside down world. lowering the front end will open the top of the coupling.

Make VERY SMALL ADJUSTMENTS! It will not be far out and mark your engine mount bolt head positions before you move anything!
That way you can get it back to the starting point. Us a pry bar use small "bumps" the check the gap all around!

Dave

Went to the boat today and had excellent luck. We removed the plastic piece between the plates on the transmission and the shaft, slid the plates together, used a feeler guage and learned the top was .006 and the bottom was 0. We lowered the back engine mounts 1/4 turn on starboard and 1/2 turn on port, slid them together and had less than .002". Reinstalled everything and went for a test drive. It was not really as easy as it sounds standing on our heads for several hours rounding nuts busting nuckles ect. But the boat did better than it has ever done, had vary little vibration until we hit 4000 rpm. I plan to get a new prop over the winter but feel it is good to go.

Thanks everyone for you help and advice. I printed the comments and read them and we went along.

Thanks Again

John