Frank Langer
1984 Ericson 30+, Nanaimo, BC
We had some new vibration on our boat with the engine running, following installation of a new transmission by a diesel mechanic. I hoped it might improve on it's own once the transmission wears in a bit, but that didn't happen.
I read up on engine alignment, and debated whether to attempt it at the risk of breaking everything, as I hadn't done this before and am not mechanically inclined. I decided to proceed today, and achieved some success, so would encourage any anxious newbie to try this if they suspect their engine is not aligned correctly. The books said that if I could turn the drive shaft by hand, the alignment is probably close, so I didn't know if I would gain anything by trying to improve the alignment. As well, the diesel mechanic had told me that he got the alignment "very close, within about 4/1,000 of an inch". Also, David Pascoe, who writes alot about boats, says that trying to be too perfect about engine alignment is unrealistic as the cutless bearing is rubber and will allow movement, the engine will vibrate and shift a bit due to torque, throwing the alignment off, the hull flexing will affect alignment, etc.
I undid the bolts at the transmission/drive shaft coupling (4 bolts with nuts easily accessible). Though very tight, I was able to undo them with normal wrenches, without dropping them into the bilge. I moved the prop shaft back slightly by hand, then snugged it up again to the coupling, and then measured the space between the faces of the coupling at the top, bottom and both sides with an automobile feeler gauge in thousandths of an inch. The books say that differences of up to 0.001 per inch diameter of the coupling face are acceptable; my coupling is about 3" in diameter, so the tolerance on my boat shouldn't exceed 3/1,000s of an inch. The measurements were slightly different, but not as much as I had expected:
0, 5, 6, 4.
I mainly worked on the front motor mount on my universal 5416, as it is easily accessible, and the up/down adjustment is straight forward. It took many small adjustments of the nut to raise or lower the front of the engine just the right amount to achieve an equal gap at the top and bottom of the coupling. I found it important to raise or lower the bottom nut, and then also to tighten down the top locking nut--not doing so gave a false reading, as tightening the top nut slightly changed the position of the engine as well. Raising/lowering the front of the engine also slightly affected the measurements at the sides of the coupling, which I hadn't expected.
I was able to achieve measurements of 0, 2, 4, 3 thousandths. I was unable to shift the engine side to side as the side/aft motor mount nuts are almost impossible to reach with normal tools and the engine is too heavy to move by myself. The books say you can hit it with a hammer to move it, but there isn't any swing room, and I don't like the idea of hitting the engine with a hammer.
I decided that maybe I was close enough to be ok as the top/bottom were within 1/1000 and the side to side were within 4/1000, and replaced the nuts and bolts on the coupler, tightening them hard on opposite sides so they tightened evenly, and so they can't come undone.
I took the boat for a test run, and the vibration that had been quite pronounced at 5.5 to 6.2 knots was essentially gone. There is still a vibration at about 4.2 knots, but I'm told that all diesel engines have a speed/RPM where the engine harmonics make everything vibrate. But otherwise, the engine runs smoothly now with almost no engine vibration, and no vibration discernible when I put my hand on the transmission. I can turn the drive shaft by hand fairly easily, and it all feels smooth.
I would have liked to get the measurements perfectly even all round, but I didn't think that was possible; and I'm pleased that I got it closer than the professional diesel mechanic had done, and my annoying vibration is gone. I'm surprised that the small improvement in my measurements over how the diesel mechanic left it could make such a noticeable difference.--just a few thousandths of an inch!
So for those who haven't attempted this, and suspect their alignment may be a problem, I think this is one job that is relatively easy for an amateur to do.
Frank
I read up on engine alignment, and debated whether to attempt it at the risk of breaking everything, as I hadn't done this before and am not mechanically inclined. I decided to proceed today, and achieved some success, so would encourage any anxious newbie to try this if they suspect their engine is not aligned correctly. The books said that if I could turn the drive shaft by hand, the alignment is probably close, so I didn't know if I would gain anything by trying to improve the alignment. As well, the diesel mechanic had told me that he got the alignment "very close, within about 4/1,000 of an inch". Also, David Pascoe, who writes alot about boats, says that trying to be too perfect about engine alignment is unrealistic as the cutless bearing is rubber and will allow movement, the engine will vibrate and shift a bit due to torque, throwing the alignment off, the hull flexing will affect alignment, etc.
I undid the bolts at the transmission/drive shaft coupling (4 bolts with nuts easily accessible). Though very tight, I was able to undo them with normal wrenches, without dropping them into the bilge. I moved the prop shaft back slightly by hand, then snugged it up again to the coupling, and then measured the space between the faces of the coupling at the top, bottom and both sides with an automobile feeler gauge in thousandths of an inch. The books say that differences of up to 0.001 per inch diameter of the coupling face are acceptable; my coupling is about 3" in diameter, so the tolerance on my boat shouldn't exceed 3/1,000s of an inch. The measurements were slightly different, but not as much as I had expected:
0, 5, 6, 4.
I mainly worked on the front motor mount on my universal 5416, as it is easily accessible, and the up/down adjustment is straight forward. It took many small adjustments of the nut to raise or lower the front of the engine just the right amount to achieve an equal gap at the top and bottom of the coupling. I found it important to raise or lower the bottom nut, and then also to tighten down the top locking nut--not doing so gave a false reading, as tightening the top nut slightly changed the position of the engine as well. Raising/lowering the front of the engine also slightly affected the measurements at the sides of the coupling, which I hadn't expected.
I was able to achieve measurements of 0, 2, 4, 3 thousandths. I was unable to shift the engine side to side as the side/aft motor mount nuts are almost impossible to reach with normal tools and the engine is too heavy to move by myself. The books say you can hit it with a hammer to move it, but there isn't any swing room, and I don't like the idea of hitting the engine with a hammer.
I decided that maybe I was close enough to be ok as the top/bottom were within 1/1000 and the side to side were within 4/1000, and replaced the nuts and bolts on the coupler, tightening them hard on opposite sides so they tightened evenly, and so they can't come undone.
I took the boat for a test run, and the vibration that had been quite pronounced at 5.5 to 6.2 knots was essentially gone. There is still a vibration at about 4.2 knots, but I'm told that all diesel engines have a speed/RPM where the engine harmonics make everything vibrate. But otherwise, the engine runs smoothly now with almost no engine vibration, and no vibration discernible when I put my hand on the transmission. I can turn the drive shaft by hand fairly easily, and it all feels smooth.
I would have liked to get the measurements perfectly even all round, but I didn't think that was possible; and I'm pleased that I got it closer than the professional diesel mechanic had done, and my annoying vibration is gone. I'm surprised that the small improvement in my measurements over how the diesel mechanic left it could make such a noticeable difference.--just a few thousandths of an inch!
So for those who haven't attempted this, and suspect their alignment may be a problem, I think this is one job that is relatively easy for an amateur to do.
Frank
Last edited: