Vibration after new mounts

[Eric]

This winter during lay-up I had all engine mounts replaced on my 2007 Sea Ray with QSB425s. Cummins Minnesota replaced the mounts, as well as serviced all the boat’s coolers and replaced hoses and clamps.

With the boat now back in the water, Im noticing substantially more vibration than was present with the old mounts. At idle, while not in gear I barely feel anything thru the hull. However, when in gear im getting a very sharp, high frequency vibration with lower rpm settings from 700-1200, and above 1700 RPMs its a more pronounced lower frequency vibration that shakes the whole boat. You can visibly see the bow rails wobbling as if a major earthquake is underway.

I’ve also noticed that my port motor now reports significantly higher fuel flow and engine load than the starboard motor. In some cases its burning upwards of 3gph more than the other motor. Even at low RPM, its using a gallon per hour more.

Also of note is I had both props reconditioned over the winter, and they were both dynamically balanced by a very reputable prop shop in the Minneapolis area.

I had Cummins back to the boat to check alignment, and surprisingly the tech seemed skeptical that such a procedure was necessary. I also asked him why some of the mounts seemed to be much more depressed than others, and he explained that “some mounts break in quicker than others”.

The tech seemed completely unaware of a need to distribute the weight properly, as well as align the motors after new mounts were installed. He even told me that “we put new motors in boats all the time and never touch anything else!”

I’ve lost confidence in his ability to properly finish his job, but I cant seem to find anyone willing to help in the Minneapolis area.

Any suggestions or referrals from this community? Im currently reluctant to use the boat as to not cause any further damage.

Topic

[donald roth]

Singing could be the shaft rubbing in the stern tube or cutless bearings.
It could be even the damper, alternator, water pump, idler pulley, etc, though that s not likely given that you have that wobble/ vibration issue too.
A real alignment includes the entire drive train, much more involved than just getting the couplings to agree.
Tony’s comment about the prop key is right on, all the prop to shaft lapping in the world won’t fix an improperly fitted key !

[William Walter]

Vibration

Have you verified props are not fouled in any way since you put it in.I picked up some line going trough a weed line last week.Didnt know I picked up the line but symptoms were increased vibration and an increase in fuel flow.I was able to dive on it and remove the line.Bill

[Tony Athens]

“its totally smooth until about 1600 RPMs, and then a very pronounced wobbling like vibration develops that shakes the whole boat. You can visibly see the bow-rails shake back and forth”.

IMO ,this symptom is not a “mount issue”, this is an installation issue related to the prop and or vert bad shaft alignment to the engine.

The prop could easily be riding on the key and not properly seated on the taper. Seen this many times due to improper prop installation.

As to alignment–In the harbor at low/idle speeds, do you see any movement in the shaft that it looks to be walking the gear side-to-side as it rotates–watch closely. If it is, this is related to the shaft or the coupling/alignment. If a mechanical really found it .015 out, then who knows what else was sloppily done. BTW, .001″ per inch of couple diameter is the spec… so a 5.75″ OD diameter couple should be under .006″-ish max. Less is always better though.

Typically, if you feel it in your pants at higher speeds. it’s prop related. Rails wobbling or overhear electronics shaking is a sure sign of that.

Tony

[Fireisland1]

Why did you decide to replace all the mounts? Was there an existing problem?

[Eric]

Rob,

Thanks for the thoughts. My instincts also are to have the props checked again. The shop that did the overhaul has a very good reputation and is highly regarded locally and has said they are happy to recheck their work. It’s obviously problematic to pull props with the boat in the water on a lake with limited ability to haul.

With that said, I don’t think it’s the “singing” issue with the starboard engine. I am aware of and have heard that phenomenon first hand, and this is not that. It’s a very sharp piercing physical low amplitude high frequency vibration that adds a deep harmonic rumble to the background noise of the boat and can be felt through the entire hull. It almost seems like the engine is hard mounted directly to the stringers and you feel it directly as if there were no soft mount at all.

[Rob Schepis]

Sounds like one prop is “singing” and the other is “out”. IMO, props need to be pulled and gone through by a first class prop shop. I know you said they were just done. The one that is out could have left the shop unbalanced or could have had a blade twisted on reinstall. I’ve seen props installed by chocking a block of wood between the blade tip and the hull and then tightening the nuts with a big wrench and cheater bar. This WILL twist the blade. Props need to be chocked in tight at the hub if the shafts cannot otherwise be locked for tightening. As to the one that is “singing” you can Google that – it’s all about the way the edge was finished (actually, not finished) when the prop was reconditioned. They need to fix the edge geometry.

[Eric]

UPDATE

I hired another service guy to come check alignment who knows what he is doing. He found one motor 15 thousandths out, which is 5 times the allowable limit of 3 thousandths. He was able to get all measurements below 3 thousandths, and it definitely made an improvement.

I was not able to sea-trial the boat with the mechanic, however on the next run I noticed the boat still has significant vibrations. I did some more playing around and found that if I put the port motor in gear, its totally smooth until about 1600 RPMs, and then a very pronounced wobbling like vibration develops that shakes the whole boat. You can visibly see the bow-rails shake back and forth.

If I do the same exercise with only the Starboard motor in gear, from about 750-1100 RPMs I experience a very sharp piercing type high frequency vibration that eventually goes away above about 1100 RPMs and I feel no evidence of the wobbly vibration that I get on the other motor. However, the sharp vibration manifests in a very uncomfortable ride at low RPM and adds significant perceived noise to the boat’s occupants.

With both engines synced under normal use, I get both the high frequency effect at low RPMs from the starboard motor as well as the wobbly shaking at higher RPMs from the port motor. Its very frustrating.

I know these are very difficult issues to deduce and diagnose over the internet, but any tips you all may have would be vert appreciated.

Remember, all 8 engine mounts are brand new, and both props were repitched and reconditioned including dynamic balancing over the winter. They were re-installed professionally and properly lapped to the shafts.

Thanks
Eric

[Philip]

Wouldn’t be the first time someone tried to align an engine with the boat on blocks. The hull changes shape in the water and a land alignment is just an initial. Get the boat in the water for a good week to let the hull relax to its natural shape and then have a competitor to mechanic align the engines again with no more than 4 thousands tolerance,.. less is better.

Phil

[Rob Schepis]

Ouch, I feel your pain. That shop needs to stay with RV’s and horse trailers. Definitely time for a new mechanic. Have you tried the Sea Ray forum?

Do you have a “non-marine” mechanic with a working brain who is willing to try something new. Engine alignment is not rocket science – it just takes an understanding of how things go together, a taste of geometry and the know how to use simple hand tools. If you might have such a candidate (or possibly you and skilled buddy) then a one-on-one paid consultation just might be your way out of this.

[Author]

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