Shaft vibrates

[Propnut]

View attachment 102084

Just installed a factory reman 6BT 210 Cummins and new ZF 280-A gear in the boat. Runs and performs great, except for a shaft vibration. Coupling is aligned, engine mounts are new and there was no vibration prior to installing the new engine and gear. I did not reinstall the shaft saver per Tony Athens recommendation. I have read an article that stated if the packing gland is rigid with a cutlas bearing in it, a shaft saver must be used, which is what I have. I’m curious if others with a rigid packing gland are using a shaft saver or not?

 

[Comodave]

My boat had drive savers in it when I bought it. I just pulled and reinstalled the port engine and decided to not reinstall the drive savers since you can’t really align the engine very well with them. I had a spacer made to take up the gap from the drive saver. I put new hose, packing and clamps on my stuffing box. We just launched today so I don’t know about vibration yet since we just idled it from the haul out home about 1/2 mile. Not sure how different our stuffing boxes are.

 

[Comodave]

Here is a better photo.

 

[catalinajack]

Comodave is correct; aligning an engine with a Drivesaver more precisely than without is difficult. About a year ago I had all of my cutless bearings replaced, four on each side including one at the water side of the stuffing box. I also eliminated the Drivesavers with a machined spacer. My boat has no vibrations after an engine alignment in the water. A Drivesaver is not required if a boat happens to have a cutless bearing at the stuffing box at least mine is not.

As a side note, I removed the Drivesavers because I suffered a failure. I shattered a Drivesaver when attempting to back off a shoal and, no, I did not hit an object in the water or another portion of the shoal. It just broke apart with applied torque. I am no fan of them. Plus, their value in saving damage is suspect at least according to Steve D'Antonio in a thread some time ago. Consider getting rid of the Drivesaver and installing a spacer. They can be had from the Spurs company, the folks who make prop shaft line cutters.

 

[Propnut]

Comodave is correct; aligning an engine with a Drivesaver more precisely than without is difficult. About a year ago I had all of my cutless bearings replaced, four on each side including one at the water side of the stuffing box. I also eliminated the Drivesavers with a machined spacer. My boat has no vibrations after an engine alignment in the water. A Drivesaver is not required if a boat happens to have a cutless bearing at the stuffing box at least mine is not.

As a side note, I removed the Drivesavers because I suffered a failure. I shattered a Drivesaver when attempting to back off a shoal and, no, I did not hit an object in the water or another portion of the shoal. It just broke apart with applied torque. I am no fan of them. Plus, their value in saving damage is suspect at least according to Steve D'Antonio in a thread some time ago. Consider getting rid of the Drivesaver and installing a spacer. They can be had from the Spurs company, the folks who make prop shaft line cutters.

I don’t have a hose between my cutlas bearing and the packing gland, mine is a one piece rigid unit. Yours has a cutlas bearing behind the packing and so does mine, so I’m thinking that I should be good with no isolator. I had some corrosion on the shaft right where the packing runs, so I’m replacing the shaft, shaft coupler,all three cutlas bearings and having the prop checked.
If it still vibrates, I’ll just shoot myself! LOL

 

[Comodave]

I will see what happens with mine when we get a chance to run it a bit. Right now I have to get the boat cleaned up and take the crane apart in the salon so we can get it back to normal. I had good success working with Spurs to have them make a spacer for me. It fit perfectly. The only downside was that it cost $520. But I didn’t have any extra shaft to slide forward to get to the transmission without the drive saver. So spacer it was.

 

[O C Diver]

Couple of thoughts:
Check the engine alignment now that all your new stuff has had a chance to settle.

Same shaft and propeller? Did you have them checked before installing them? What speed was shaft turning with the old engine and transmission versus the new one? How does the HP fuel burn compare? Have you increased speed? In what RPM range do you get the vibration?

Ted

 

[kapnd]

It should run smoother with the spacer in, rather than the drivesaver, as the drivesaver can flex.
Drivesavers are especially scary when doing any hard reversing, they visibly flex, allowing the prop and shaft to move back a bit, which is straight into the rudder if the thing lets go!

 

[catalinajack]

It should run smoother with the spacer in, rather than the drivesaver, as the drivesaver can flex.
Drivesavers are especially scary when doing any hard reversing, they visibly flex, allowing the prop and shaft to move back a bit, which is straight into the rudder if the thing lets go!

Yup, as I said in Post #4, I blew out a coupling in hard reverse. As for the shaft backing out into the rudder, i have ring anodes installed on the shafts close to the stuffing box that prevents a shaft from backing out too far. As Dave asked, have you had your shaft checked for trueness. When I had my cutless bearings replaced the yard sent the shafts out. Both were slightly bent. They were able to straighten them. Between the new bearings, straightened shaft, prop tuning, and engine alignment, no vibrations. By the way, if you were not aware, engine alignments must be done in the water.

 

[FF]

The spacer might not be well done.


Chuck it in a lathe to see of its round .

 

[kapnd]

Can you easily turn the shaft by hand?
It may be dragging in the cut less bearing, 1 piece stern tube/stuffing boxes require precise installation. If it’s slightly cocked in any direction, it puts unequal pressure on the bearing, and the stuffing, and can cause a rumbling and vibration.
A machined sleeve should be used for installation in place of the bearing, as the bearing is soft, and too sloppy for good alignment.
Your motor mounts can add to your troubles, if they are worn or too soft.