Vibration after new motor mounts

This winter during lay-up I had all engine mounts replaced on my 2007 40 Sundancer 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 3 gph more than the other motor. Even at low RPM, it's 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 the job, but I cant seem to find anyone else 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.

I would have a conversation with the Cummins service manager.

Sounds like an alignment issue. Your assessment of the tech seems spot on.

Sounds more like a cylinder misfire to me. Is your shaft log moving underway? Or just the engine? Alignment issues will have the shaft log dancing. A bad injector or fuel pump will have the engine vibrating.

Any boatyard can do the alignment. I would ask Cummins to pay for this if it is out of alignment since their tech seems confident it’s fine

Any boatyard can do the alignment. I would ask Cummins to pay for this if it is out of alignment since their tech seems confident it’s fine

NotHerDecision said:

Any boatyard can do the alignment. I would ask Cummins to pay for this if it is out of alignment since their tech seems confident it’s fine

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So far, I cant even get Cummins to call me back about it. And finding a boatyard willing and able to do the job in Minnesota is proving to be harder than you'd think...

I’m not familiar with any of the yards up there but I do think you need to verify the alignment before you cause other issues.

Maybe make a post asking about Minnesota boatyards. There are some northern folks who may be able to help. Also reference the map of members.

Not good for your cutlass bearings! The binding due to misalignment could cause a higher fuel flow.